[advances in food research] advances in food research volume 23 volume 23 || wheat germ

WHEAT GERM

S . R . SHURPALEKAR AND P . HARIDAS RAO

Flour Milling and Baking Technology Discipline Central Food Technological Research Institute

Mysore. India

I . Introduction .................................................... 188 I1 . Structural Components of the Germ . ............................. 190

A . Structure of the Germ .......................................... 190 B . Components of the Germ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 C . Methods for Separation and Determination of StructuralComponents . . . . . 195 D . Germ Content and Composition of Its Structural Components . . . . . . . . . . . 196

Ill . Separation of the Germ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 A . Separation of Whole Germ ...................................... 198 B . Separation of Flaked Germ ....................................... 199 C . Physical Characteristics of Mill Germ .............................. 200 D . Air Classification of the Germ .................................... 201

IV . Chemical Composition of the Germ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 A . DissectedGerm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205

B . Mill Germ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 C . Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241

V . Nutritive Value of the Germ ........................................ 242 A . Nutritional Evaluation by Chemical Methods ........................ 242 B . Nutritional Evaluation by Biological Methods ........................ 244 C . Supplementary Value of Wheat Germ .............................. 246 D . Effect of Processing on the Nutritive Value of the Germ . . . . . . . . . . . . . . . . 249 E . Effect of Supplementing the Germ with Amino Acids ................. 253 F . Toxic Factors in the Germ ...................................... 255 G . Summary .................................................... 258

VI . Storage and Stabilization of the Germ ................................ 258 A . Storage Studies ............................................... 259 B . Methods of Stabilization of Wheat Germ ............................ 263 C . Effect of Storage and Stabilization on the Nutrients ................... 270 D . Summary .................................................... 273

VII . Wheat Germ and Bread-Making Quality ............................... 273 A . Earlier Studies ................................................ 273

187

188 S. R. SHURPALEKAR AND P. HARIDAS RAO

B. Recentstudies ............................................... 277 C. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281

VIII. Food Uses of the Germ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 8 2 A. Bakery and Pastry Products . . . . . . . . . .......................... 2 8 2 B. Supplement for Cereals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 C. Germ Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Fermented Foods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Vitamin Concentrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 F. Animal Feeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

IX. Research Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 8 9

I . INTRODUCTION

Wheat is the major staple food in the dietary of people in Europe, Australia, North and South America, and some parts of Asia. It accounts for 20 to 80% of the total food consumption in various regions of the world.

Wheat grain consists of the endosperm, the bran (layers of seed coat), and the germ, which account for 81 to 84%, 14 to 16%, and 2 to 3% of the grain, respectively. Most of the wheat produced in the world is processed in commercial roller flour mills into white flour or semolina, for use in the manufacture of bread, cookies, crackers, and macaroni products. In developing countries, it is processed into whole-wheat flour or semolina in hammer or disc mills of widely varying capacities. These products are used in preparing sweet and savory items for breakfast or other meals, snacks, chaparis (unleavened pancakes), whole- wheat bread or rolls, etc.

Commercial milling of wheat into flour aims at the maximum extraction of the endosperm with the minimum possible contamination by bran and the germ, which form the by-products of the flour milling industry and are generally used in animal feed formulations. Depending on the extraction rate, varying proportions of the germ also finds their way into the flour during milling. This is not desirable, as the presence of the germ affects the storage stability as well as the baking quality of the flour.

Wheat germ is a unique source of highly concentrated nutrients. It offers three times as much protein of high biological value, seven times as much fat, fifteen times as much sugar, and six times as much mineral content when compared with flour from the endosperm. In addition, wheat germ is the richest known source of tocopherols (vitamin E) of plant origin and also a rich source of thiamine, riboflavin, and niacin. The presence of large amounts of fats and sugars makes wheat germ highly palatable. Toasting is reported to improve its flavor.

Early investigators reported that, qualitatively as well as quantitatively, cereals are poor sources of protein as indicated by their low biological value or protein

WHEAT GERM 189

efficiency ratio. Interestingly enough, wheat germ proteins have been classed with superior animal proteins.

In view of its high nutritive value and palatability, wheat germ offers an excellent source of proteins and vitamins for fortification of food products. Its use in bakery products, especially bread and biscuits, has received special attention. In many of the western countries, it is also used as a breakfast cereal.

The only drawback in the extensive utilization of wheat germ has been its poor storage stability, owing to the presence of large amounts of fats and of oxidative as well as hydrolytic enzymes, which render the product highly susceptible to rancidity (Kuhl, 1941). Many processing methods have been reported to improve the stability and hence the shelf life of wheat germ (Rothe, 1963). Some of the heat processing techniques are also reported to improve its nutritive value by the destruction of the antinutritional factors present in the germ.

The wide prevalence of protein and calorie malnutrition among the vulnerable segments of the population in many developing countries has been reported by

TABLE I WORLD PRODUCTION OF WHEAT^

Regionlcountry

Economically developed North America

United States Canada

Western Europe France Germany

0 c e a n i a Other developed

Economically developing Africa Latin America

Argentina Near East Far East

India

Economically centrally planned Asia

Europe, USSR China

Production (million metric tons)

56.56

56.1 1

7.04 2.29

Total 122.00

6.16 12.45

26.34 33.93

Total 78.87

34.86

1 1 1.88

WORLD TOTAL 347.60 Total 146.73

42.04 14.51

18.12 6.61

8.10

26.48

34.50

'FA0 (1972).

190 S . R. SHURPALEKAR AND P. HARIDAS RAO

several nutrition workers (Scrimshaw and Behar, 1959; Bressani and Elias, 1968; Narayana Rao and Swaminathan, 1970). Consequently, a worldwide search has been in progress during the last few decades t o discover hitherto unknown or unutilized resources of food nutrients to meet the challenge of hunger. In addition t o oilseed meals, wheat germ, being a by-product of the flour milling industry, forms one of the most potential sources of much-needed proteins, calories, and vitamins a t a relatively low cost.

Based on a world figure of about 3 5 0 million metric tons of wheat per annum (breakdown given in Table I), about 7 million metric tons of wheat germ providing nearly 2 million metric tons of protein and approximately 25 billion calories are potentially available. Thus, a tremendous scope exists for harnessing wheat germ t o improve the nutritional status of the needy millions.

Even though a considerable amount of research has been carried out by several workers, no comprehensive review on wheat germ covering various aspects relating t o processing, nutritive value, and utilization has been published so far. The available literature on the structure, separation, composition, nutritive value, stabilization, and food uses of wheat germ is reviewed in this chapter.

II. STRUCTURAL COMPONENTS OF THE GERM

Several workers (Vogl, 1899; Tschirch and Oesterle, 1900; Percival, 1921; Winton and Winton, 1932; Hector, 1936; Hayward, 1938; Fairclough, 1947; Gassner, 1951) have investigated the structure of various parts of the wheat kernel including that of the germ. Knowledge of the structure of the germ and the tissues surrounding it was found t o be important for its efficient separation during the milling process and for its utilization. The related studies were restricted to some aspects of its structure and its relation t o water penetration into the starchy endosperm of the wheat kernel during the conditioning operations of tlie milling process. Milling efficiency was found t o be largely dependent on water penetration during conditioning. Knowledge of the microscopic structure of the germ has also been useful in tlie work of quality control laboratories of wheat-based industries as well as in quality evaluation of animal feed formulations.

A. STRUCTURE OF THE GERM

The germ is a separate and distinct part of the wheat kernel. Partly embedded in the endosperm, it is located at the base of the wheat kernel. There are natural

FIG. 1 . Wheat kernel (Pawnee variety) bisected longitudinally through the crease (20X). This is a composite p h o t o p p h tliat givcs an idealized view of the cut surface at the right and of onc flank of the crease at the left (by courtesy, Northern Utilization Research Branch, U.S. Dept. Agr., Peoria, Illinois).

BRUSH

A

B

C

D

, OUTER PERICARP

ALEURONE LAYER

STARCHY ENDOSPERM NUCELLAR PROJECTION

PIGMENT STRAND

VASCULAR BUNDLE PERICARP I N CREASE REGIC

EN DOSPERM CAVITY

SCUTELLUM

COL EOPTILE

PLUMULE

EPIBLAST

PRIMARY ROO COLEORHIZA SEED C O A T

T

FIG. 2. Transections of wheat kernel (Pawnee variety) at planes A, B, C, and D indicated in Fig. 1 (by courtesy Northern Utilization Research Branch, U.S. Dept. Agr., Peoria, Illinois).

WHEAT GERM 193

lines of separation of the germ from the endosperm and the bran. Thus, it would appear that the germ could be easily separated even from the dry kernel. Actually, the tissues of the germ and the endosperm are in intimate contact with each other, probably through a cementing layer in between. Moistening the wheat may help in weakening the cementing layer between the two structural components (Bradbury el al., 1956d), as in corn (Wolf el a t , 1952), and ease their separation.

Structurally, the wheat kernel may be divided into three main parts (Fig. 1): (1) the germ (the embryo), which produces the new plant; (2) the endosperm, which provides the food for the new plant when the embryo starts to grow; and (3) the various outer coverings, collectively called bran, which protects the

FIG. 3. Longitudinal section of germ cut parallel to the crease (44X). E. endosperm: VS, ventral scale; Cp, coleoptile; Sc, scutellum;, El, epithelium; FL, foliage leaves; P1, plumule; SA, stem apex; B, bran; ScN, scutellar node; Eb, epiblast; PR, primary root; Co, cortex; VC, vascular cylinder; RC, root cap; Cr, coleorhiza; SC, seed coat.


kernel. Bradbury et al. (1956a-d) have described exhaustively the structure of the wheat kernel and its various parts, including the germ, with photomicro- graphs.

B. COMPONENTS OF THE GERM

Wheat germ is composed of two major parts-the embryonic axis and the scutellum-and also the epiblast, which is of minor importance (Figs. 1, 2, and 3). On germination, the embryonic axis develops into a seedling, and the scutellum nourishes it.

1. Embryonic Axis

The embryonic axis is composed of a shoot (plumule) pointing toward the brush end of the grain and a primary root pointing toward the base. The shoot consists of a stem apex, several embryonic foliage leaves, and a protective sheath, called the coleoptile. The coleoptile is a cone-shaped sheath covered by a very delicate cuticle. Near its tip is a small pore through which foliage leaves emerge during germination. The primary root and two hairs of secondary lateral roots are protected by a sheath known as the coleorhiza. The coleorhiza is composed of parenchyma cells, covered by inner and outer epidermal layers. The walls of these cells are slightly thicker in the tip region of the coleorhiza.

2. Scutellum

The part of the germ that is attached to the side of the embryonic axis nearest to the endosperm is called the scutellum. Its convex face is embedded in the endosperm, and its slightly concave surface partly encloses the embryonic axis. The slight projection near the tip of the scutellum is called the ventral scale. During germination, the scutellum supplies food, which has been stored in the endosperm during maturation, and becomes a digesting and absorping organ for the transfer of food from the endosperm to the growing part of the embryonic axis (Percival, 192 1).

The epidermis of the scutellum, adjacent to the endosperm, is modified to form a layer of secreting cells called the epithelium. The surface of the scutellum of bread wheats is free from invaginations or “glands,” unlike corn germ. Only a few “glands” sometimes appear near the tip of the scutellum. The provascular bundle of the scutellum consists of many protoxylem and protophloem cells which have a smaller diameter than the parenchyma cells. This bundle extends from the scutellum node into the upper part of the scutellum. Near the tip of the scutellum it divides into many small branches which extend to a considerable distance. The largest proportion of the scutellum consists of unspecialized cells

WHEAT GERM

1 I 1

-Seed coat Endosperm Germ (embryo) I

I I I I

Scutellum Embryonic axis Epiblast

I Primary root Secondary

+ Epitheleum Parenchyma Provascular Plumule,

tissues including covered by lateral

coleoptile coleorhiza rootlets

- Bran

195

Wheat kernel

I

Pericorp I

Seed

(parenchyma), which form the body of the scutellum. In addition to the nucleus and the cytoplasm, these parenchyma cells contain a considerable amount of protein and fat and very little starch.

3. Epiblast

The epiblast, a scale-like structure with little morphological significance (Avery, 1930), is present opposite the scutellum, on the other side of the embryonic axis.

Different parts of the germ are clearly shown in Figs. 2 and 3. The relationship of the different parts of the wheat kernel with special reference to the germ is given in Fig. 4.

C. METHODS FOR SEPARATION AND DETERMINATION OF STRUCTURAL COMPONENTS

The relative merits of different methods for separation of the structural components of the germ have been described by MacMasters et al. (1971).

1. Methods of Separation

a. Hand-Dissection of the Untreated Kernel. For separation of major components like the scutellum and the embryonic axis, hand-dissection is accurate,

196 S. R . SHURPALEKAR AND P. HARIDAS RAO

but it is laborious and time-consuming. Also, the separation of all the constituent parts of these major components cannot be achieved by this method.

b. Hand-Dissection of the Kernel after Soaking It in Water. Soaking the kernel in water prior to dissection results in greater accuracy. However, soaking may alter the chemical composition of different parts, owing to the movement and redistribution of soluble matter. This method is also time-consuming.

c. Maceration of the Kernel by Mechanical Treatment in Chemical Rea- gents. This method is comparatively quick, and many samples can be dissected in a short time. The possibility of change in the chemical constituents due to their movements or due to absorption by the reagent is the main limitation of this method.

d. Separation of the Components in Organic Liquids after Mechanical Treat- ment of Mill Products. This method is also very rapid, but complete separation of all structural components is not possible.

2. Quantitative Determination of Structural Components

Most of the quantitative data are obtained by separating the kernel components by the above-mentioned methods and immediately weighing the products. In some cases, the quantitative data are calculated by comparing the data on the chemical composition of different components of the kernel under study with those of well-defined pure components. The reliability of this method depends on the correctness of the data on the chemical composition of the pure structural components, which are generally hand-picked from mill products. Although this method is not as accurate as the hand-dissection and weighing method, larger numbers of samples can be handled.

D. GERM CONTENT AND COMPOSITION OF ITS STRUCTURAL COMPONENTS

According to Bailey (1938), durum wheat has a higher germ content, 2.9476, followed by soft wheat, 2.6676, and spring wheat, 2.23%. Recently, Matveef (1965) observed that hard wheats contain a higher proportion of the germ (2.4 to 3.9%) than soft wheats (2.1 to 3.2%). Also, smaller kernels of any one variety have a smaller proportion of the germ than large kernels.

The data given in Table 11 on the composition of the germ and its component parts indicate that the weight of the germ in relation to kernel weight as well as the proportion of the embryonic axis and the scutellum varies widely. These variations have been attributed to varietal differences, kernel size, and method of dissection. In general, the proportion of the scutellum was found to be higher than that of the embryonic axis.

WHEAT GERM 197

TABLE I1 COMPOSITION' OF WHEAT GERM AND ITS COMPONENTS

Number of samples Total germ Embryonic axis Scutellum References -___-

4 (France) 1.2 -1.5 - - Girard and Fleurent (1899) 4 2.5 -3.6 1.0 -1.6 1.4 -2.0 Hinton (1947, 1959)

5 (Australia) 3.10 1.40 1.70 Hinton (1962) 8 (Russia) 2.56-3.25 - - Grisclienko (1 935) - 2.8 -3.5 - - Percival (1921)

- Matveef (1 965) - 2.1 -3.9 - 156 2.0 -3.1 - - Mambish (1953) - 3.4 -3.8 - - Kazakov (1947) - 2.64 1.25 1.39 Dubois er al. (1960) 3 3.2 -3.8 - - Morris et al. (1945)

11 - 0.90-1.5 1.30-1.80 Hinton (1944) - - 1.37 1.09 Blain and Todd (1955)

20 (American) 2.64 1.25 1.39 Bailey (1938)

uPercent of wheat kernel, on a moisture-free basis.

1 1 1 . SEPARATION OF THE GERM

Wheat germ is a by-product of the roller flour milling industry. Its separation from other milled products is important for the following reasons: (1) It adversely affects the keeping quality of flour and other mill feeds. Stevens (1959) reported that 23 to 34% of the oil in flour originated from the germ, owing to expression of the oil during rolling. The presence of highly unsaturated germ oil in flour decreases its storage life because of oxidative rancidity (Kuhl, 1941). (2) The presence of the germ in flour was reported to affect the baking quality and color of the flour (Bull, 1937; Pomeranz et al., 1970b). ( 3 ) Wheat germ is a rich source of protein of high nutritive value, B-group vitamins, and tocopherols, and a potential nutritious food supplement. It thus has great commercial value, fetching more than double the price of other mill feeds, and can be used with advantage in the preparation of speciality breads and also as a vitamin E concentrate.

Even though wheat contains 2 to 3.5% of germ, only about 1% is recovered during normal milling operations for the following reasons: (1) Most of the scutellum portion goes into the flour stream, as it is more friable, like the endosperm. The embryonic axis gets flattened between the rollers and can be recovered by proper sieving techniques. (2) Breakage of some of the germ portions into small pieces occurs in between the rollers. The broken portions escape into the floury portion and are not recovered. ( 3 ) Also, some of the germ


portion is lost during screen-room operations such as handling, scouring, wash- ing, and brushing.

There are two ways by which the germ can be separated in the mill. One method is to separate it in the break system itself, in the form of whole germ, by using a “germ separator” as ancillary equipment. In the other method the middlings containing the germ particles are passed through the reduction rolls, where the germ gets flattened and is removed by sieving.

A. SEPARATION OF WHOLE GERM

I . Use of the Germ Separator

A good account of the separation of the germ was given by Lockwood (1952). The germ must be separated before the particles of the endosperm, germ, and bran portions become very small in the break rolls. The particle size should be such that they will not pass through a 28-mesh sieve. The scutellum was present in the stocks released from the second break onward. After the second break it was released mainly in the particle size of coarse semolina, and further grindings produced an increased proportion of fine particles. The first three breaks cut up very little germ and left most of it substantially intact. However, in the later rolls most of the germ was either cut up or overtailed the scalpers, and escaped with the bran. Thus it is imperative that the germ be separated before the middlings enter the fourth break.

Kent et al. (1944) found that the release of the scutellum in the break system was earlier in soft wheat than in hard wheat. Further, Kent et al. (1949) reported that the release of the scutellum and the embryo portions depended on the moisture content of the wheat. The higher the moisture content, the higher will be the amount of the scutellum that can be removed, as it is more friable at a low moisture content.

Separation of the germ from the other stock was achieved by using a Simon germ separator, which was introduced on the feed to the fourth-break fine rolls. Here much of the germ could be recovered intact. The separator was fed by a stock which was sifted through a No. I6 and over a No. 28 fine wire cover. The separation of the germ from the stock was carried out by using an aspiration technique of increasing intensity. The feed contained 80 to 95% of light particles of the endosperm and bran, and the remaining heavy particles were the germ. To prevent entanglement of the germ with other light material, the stock was subjected to a large volume of air moving at 380 to 440 cfm in successive controlled aspirations of increasing intensity.

Uniform stock was fed to each aspiration channel by a patented device consisting of oscillating platforms which push the material under spring-controlled feed gates. A controlled rate of airflow was obtained by careful design of

WHEAT GERM 199

the air channels and the number of curved vanes. The velocity of the first aspiration was adjusted so that only about 30% of the lighter particles was lifted out. The second aspiration was stronger and lifted some more of the lighter stock. The third aspiration lifted the remaining lighter particles except the germ. The aspirated stocks were fed to the fourth-break rolls. The separated whole germ was fed in between the smooth rollers to get the germ flaked. Rolling was done on a conventional 40-inch roller 10 inches in diameter. The speed of the rollers was adjusted in a 5:4 ratio.

Purification of the germ from the bran particles could be carried out by using a plansifter, fitted with 18W and 24W sieves. The overtails form the finished pure germ product. The cut-up germ from the first three break rollers finds its way to the reduction rollers along with coarse semolina through the purifier. It gets flattened in the reduction rollers.

The advantages in using a germ separator are higher yields of germ and a good-quality flour free of germ contamination.

2. Use of Prebreak Unit

The method of separation of the germ by using a prebreak unit was described by Jagbir Singh (1973). The machine manufactured by Sturtevant Mill Co., Boston, called the No. 6 Simpactor, was used as a prebreak unit. This machine, placed before the first break of the roller mill, breaks the wheat kernel, so as to release more free germ. The equipment, consisting of devices such as entoleters, sifters, aspirators, and rollers, separates the germ before sending the broken kernels to the first break rolls.

B. SEPARATION OF FLAKED GERM

I . Laboratory Mill

Using laboratory mill LM-400, Dimitrov et al. (1972) have reported better yields as well as better quality of germ as compared to Bulgarian standard BDS 5279-70. Later, Dimitrov (1975) also studied the effect of loading germ rolls and plansifter on the yield and oil content of wheat germ: he observed that the optimum loading was 130-150 kg per cenitmeter per 24 hours and 3500 kg per square meter per 24 hours, respectively. Free bran particles to the extent of 7.2% could be removed from the embryo fraction by air separation.

2. Commercial Mill, National Joint Industrial Council of the United Kingdom

The National Joint Industrial Council for The Flour Milling Industry (1966) has published a detailed account of separation of the germ.


Separation of the germ in the normal milling system is based on its tendency to flake in between the rollers owing to the high moisture content and fat present in the germ. Some of the germ will be cut up in the early break rolls, but most of it gets ruptured in the fourth break. This ruptured germ will have a particle size similar t o that of the middlings. The middlings containing the germ are sent to the purifiers, where most of the bran will be removed. In the purifier, the germ gets mixed up with the scratch stocks, as it is coarser than the semolina. Purified semolina or scratch stocks are sent to the reduction rolls, where the semolina gets further reduced in size, while most of the germ gets flattened and is separated by sieving. Some portion of the germ, however, gets pulverized and is difficult to separate.

This method does not require any additional equipment such as a germ separator. The main disadvantage is that the flour obtained is not of good quality, as some of the germ ruptured in the break rolls goes into the flour portion. This imparts a brown color to the flour. The keeping quality of the flour will also be affected, as during flaking in between the reduction rolls the oil of the germ gets extruded into the flour.

The mill germ thus obtained, however, contains bran and endosperm as impurities. The major contaminant of the germ is bran. Various methods have been suggested to remove the bran from the germ. Scott (1951) described a method for separation of the bran from the germ, by impinging the mill germ on a slightly moistened smooth surface. The bran particles fall off the surface, but the germ, which adheres more firmly, can be brushed off and collected separately.

C. PHYSICAL CHARACTERISTICS OF MILL GERM

a. Purify. Grewe and LeClerc (1943) determined the purity of nineteen samples of mill germ, of which only three samples were found to be pure. The remaining samples were contaminated with varying amounts of bran and endosperm. They reported that the carbohydrate content of mill germ was a good index of the purity of the germ (Section IV,B,6). Tkachuk and Irvine (1969) reported more than 20% of bran in mill germ.

b. Yield of Gem. The yield of germ depends on the method followed for separation of the germ, the moisture level of the wheat during milling, and the variety of wheat milled. It has been reported that the yield varied from 0.2% to a little more than 1.0% (Farrel er al., 1967; Calhoun et al., 1960). Farrel et al. (1967) have reported yields varying from 0.58 to 1.06% for germ samples obtained from nine varieties of wheat.

c. Density of Gem. Farrel er al. (1967) reported that the density of mill germ ranged from 18.5 to 22.6 Ib/ft3. Grewe and LeClerc (1943) found a higher

WHEAT GERM 20 1

TABLE I11 S I E V E ANALYSIS OF M I L L GERM“

~

Overt ail ings

Tyler sieves Averageb (%) Range (%)

+low +12w +14W +20w +28W Pan

0.80 11.85 21.30 50.00 9.40 5.60

0.40- 1.62 0.40-28.00

14.06-32.40 36.40-61.20 2.40-14.86 0.80-20.48

“Farrel ef al. (1967). bFor germ samples from nine varieties of wheat.

density for whole germ compared with flaked germ. The density of granular germ ranged between 117 and 143 gm per half-pint, whereas that of flaked germ ranged between 65 and 98 gm.

d. Sieve Analysis. Sieve analysis of mill germ was carried out by Farrel et al. (1967) for germ samples from nine varieties of wheat; the average values reported are presented in Table 111. Most of the germ was found in +14W and t20W Tyler sieves.

D. AIR CLASSIFICATION OF THE GERM

Pomeranz et al. (1 970a) have carried out extensive studies on air classification of pin-milled untreated and defatted germ using a Pillsbury Laboratory Model No. 1 classifier. The flow diagram of the germ air classification procedure given in Fig. 5 indicates four fine fractions-B, C, D, and E-and a coarse fraction, EE. Further work on the composition of air-classified germ was reported by Garcia et al. (1972b). They followed the method of Stringfellow and Peplinski (1966) and obtained five air-classified fractions and two coarse fractions, as indicated in Fig. 6.

1. Effect on Proximate Composition

The results of air classification studies as reported by Pomeranz et al. (1970a) are given in Table IV. They observed that air classification of original untreated germ was fast and economical, but the stability was very poor. Fractionation of defatted germ gave a more stable product. The protein increase in the major fraction was 0.9 to 1.6% in untreated germ; in defatted germ it was higher, 2.3 to 3.8%.

202 S. R. SHURPALEKAR A N D P. HARIDAS RAO

ORIGINAL FLOUR-A

100 POUNDS/HOUR

100 POUNDSIHOUR 6 DECKS FORWARD

(0" LOUVER CURTAIN CCIARSF e0eq 5800 RPM 5 0 POUNDS/HOUR

loo LOUVER CURTAIN cc FRACTION

FRACTION 10- LOUVER CURTAIN

IS / HOUR

I

2 DECKS FORWARD 35" LOUVER CURTAIN EE

I E FRACTION I FRACTION

FRACTION

FIG. 5. Flow diagram of the germ air classification procedure (Pomeranz ei al., 1970a).

Dry-Milled Wheat Germ 4

Defatted @ 11001 Pin hi l led

! X at 9,000 rpm t

Screen

c 5 0 Mesh @ -50+50 Mesh @ 114(1

-60 Mesh -60,Mesh I

I'

r

1

t

-60 Mesh Pin milled

3 X at 14.000 rpm

A; Cla$,sificat;cn

0 0 0 0

FIG. 6. Flow diagram for processing of wheat germ. Encircled numbers or letters identify samples used in the study. Numbers in boxes indicate percentage yield.

WHEAT GERM 203

TABLE IV ANALYSIS OF AIR-CLASSIFIED FRACTIONS OF WHEAT GERM@^^

Average Protein Yield Moisture particle size Ash (N X 5.45)

Source and fraction (%) (%I (microns) (%) (%I

A 100.0 6.2 10.1 4.7 29.1 B 1.8 6.7 3.9 5.0 28.5 C 11.8 6.8 6.1 5.2 30.0 D 10.4 6.6 8.4 5.1 30.7 E 19.4 7.1 10.0 4.9 27.6 EE 56.3 7.1 15.8 4.5 28.1 Bag 0.3 9.6 2.4 6.3 31.4

(petroleum ether-extracted) A 100.0 7.2 5.2 5.4 33.0 B 11.9 7.5 2.6 7.6 35.2 C 22.0 7.2 4.7 6.0 36.8 D 24.7 7.5 8.4 5.5 35.3 E 14.3 7.7 10.9 4.6 30.0 EE 26.1 7.7 19.8 3.7 26.4 Bag 1.0 8.9 1.8 7.3 31.2

"Pomeranz et al. (1970a). bExpressed on as-is basis.

Untreated germ

Defatted germ

2. Effect on Roteins and Amino Acid Composition

Pomeranz et al. (1970a) also studied the amino acid composition and starch gel electrophoretic patterns in the air-classified fractions of high as well as low protein content. The starch gel electrophoretic patterns showed that the most prominent band found in the sodium chloride extract of the germ was much smaller in the high-protein fraction of defatted germ than in the corresponding low-protein fraction.

The amino acids lysine, serine, proline, alanine, leucine, and tyrosine, and the sulfur-containing amino acids were less in the high-protein fractions than in the lowprotein fractions (Pomeranz et aZ., 1970a).

Garcia et al. (1972b) did not find any considerable effect of air classification on the amino acid levels of different fractions except the fifth one (Fig. 6). This fifth fraction had the lowest values of lysine and arginine and the highest values of leucine, alanine, and phenylalanine.


3. Effect on Mineral Content

Garcia et al. (1972b) analyzed the three major and five minor mineral elements in the different air-classified fractions of the germ and found that fraction 1 and possibly fraction 2 had higher mineral contents compared with the original samples (Table V).

4. Effect on Carbohydrates

The effects of air classification on the starch, pentosans, and sugar fractions of carbohydrates were studied by Garcia el al. (1972b). Air classification of wheat germ increased the starch content of fractions 3 and 4. Most of the pentosans were removed during screening operations, as indicated by higher values in coarse fractions A and B. Air classification had only a minor effect on modifying the pattern of sugars.

IV. CHEMICAL COMPOSITION OF THE GERM

Exhaustive literature is available on the chemical composition of mill germ. In contrast, only limited information is available on dissected germ. This may be

TABLE V

DISTRIBUTION O F M I N E R A L S ~ IN AIR-CLASSIFIED WHEAT G E R M FRACTION$

Major elements (%) Minor elements (mg%)

Defatted germ fractions Phosphorus Potassium Magnesium Sodium Calcium Iron Zinc Copper

Original Coarse fraction A Coarse fraction B Air-classified

fractions 1 2 3 4 5

Feed to classifierC

1.69 1.36 0.43 18 58 13 20 1.8 1.77 1.69 0.63 14 109 17 16 1.6 1.60 1.41 0.40 17 5 1 11 26 1.1

1.84 1.55 0.5 1 21 77 16 21 1.3 1.62 1.41 0.44 27 56 13 23 1.1 1.29 1.12 0.32 28 32 9 21 0.7 1.26 1.10 0.30 22 30 9 17 0.1 1.22 1.11 0.28 26 31 9 18 0.8 1.46 1.26 0.38 25 46 I I 2 0.9

‘Moisture-free basis. bGarcia et al . (1972b). ‘Calculated value based on yield of air-classified fractions 1 through 5.

WHEAT GERM 205

attributed to the ready availability of commercial samples of mill germ, whereas separation of the germ by dissection is quite cumbersome.

A. DISSECTED GERM

When compared with mill germ, which is admixed with bran and endosperm portions during milling, dissected germ represents the purest form of germ studied. There is more disagreement than agreement in the scanty literature on values reported for dissected germ. This may be due to the differences in the methods followed for dissection, the purity of the dissected parts, and the variety of wheat used for dissection.

1. Proteins

Morris er al. (1946) reported germ protein values for three principal classes of American wheat: 25.5% for Thorne variety (soft red winter), 24.3% for Tenmark variety (hard red winter), and 26.8% for Thatcher variety (hard red spring). Protein contents of 28.7% in the scutellum and 33.4% in the embryonic axis were reported by Hinton (1944) for eleven varieties of English wheats. Girard and Fleurent (1 899), however, found that the embryonic axis of germ from a French variety of wheat contained as much as 44% protein. It may be inferred that the embryonic axis contains a higher amount of protein than the scutellum.

2. Sugars

The sugar contents of dissected germ and its structural parts were first studied by Dubois er al. (1960) in a soft white wheat variety from Holland. The results

TABLE VI

CARBOHYDRATES O F THE EMBRYONIC AXIS A N D SCUTELLUM

FRACTION IN HAND-DISSECTED GERM^

Sugars Embryonic axis Scutellum Total germb

Total sugars‘ 22.0 18.4 20.1 Raffinosed 45.3 38.0 41.5 Sucrosed 54.7 62.0 58.5

‘Dubois et al. (1960). bCalculated on the basis of data collected for the embryonic axis and

‘Expressed as percent of defatted germ on a dry-weight basis. dpercent of total sugars.

the scutellum.


TABLE VII EFFECT OF MOISTURE CONTENT OF WHEAT ON SUGARS' IN WHEAT GERM^

Moisture 9.2% Moisture 12.3% Moisture 12.9%

Sugar Scutelfum Embryonic axis Scutellum Embryonic axis Scutellum _ _ _ _ _ . ~ _ _ _

Total sugars (%) 18.4 22.0 11.8 17.9 13.6 Sucrose (% of 62.0 54.7 57.0 56.0 51.0

Raffinose (% of 38.0 45.3 43.0 44.0 49.0 total sugars)

total sugars)

'Expressed on a dry-weight basis in defatted germ. bDubois et al. (1960).

of analysis carried out according to the method of Dubois e l al. (1951) indicated that the germ contained mainly sucrose and raffinose and only traces of glucose (Table VI). Sucrose content was higher than raffinose content in the germ and its parts. They further reported that total sugar level was dependent on the moisture level of the grain (Table VII). As the moisture increased in the wheat grain, the total sugar level decreased in the scutellum as well as in the embryonic axis fractions of the germ. This was probably due to the increase in the metabolic activity of the germ with an increase in moisture. During short storage periods, the ratio of sucrose to raffinose remained constant in the embryonic axis but decreased in the scutellum of wheat containing 12 to 13% moisture.

3. Lipids

Wide variations in the lipid content of the germ and its structural parts have been reported in the literature. This may be due to the difference in the solvent used for extraction of the lipids. When cold benzene was used for extraction, a lipid content of 12.9% in the scutellum was first reported by Girard and Fleurent (1899). Using petroleum ether extraction, Hinton (1944) found 30.3% of lipids in the scutellum, which was double that found in the embryonic aixs (15.4%). Unlike Hinton (1944), Dubois et al. (1960) found no significant difference in the lipid contents of the scutellum (1 2.6%) and the embryonic axis (1 5.3%) of germ from soft white wheats from Holland. They used diethyl ether for extracting the lipids.

Pomeranz and Chung (1965) determined the different fractions of lipids by thin-layer chromatography. The identified fractions and their quantities are given in Table VIII. Triglycerides were the main fraction in nonpolar lipids, whereas glycolipids and phospholipids were the major fractions in polar lipids.

The characteristics reported by Hinton (1944) for lipids extracted from the scutellum and the embryonic axis were: acid number, 5.3 and 3.7; iodine

WHEAT GERM 207

TABLE VlIl LIPID FRACTIONS O F DISSECTED GERM‘

Lipids Quantity (%)

Nonpolar lipids Triglycerides 7.06 Other nonpolar lipids 1.77

Unidentified 0.437 Monogalactosyl glyceride 0.559 Digalactosyl glyceride 0.725 Phosphatidyl choline 1.702

‘Pomeranz and Chung (1965).

Polar lipids

number, 116 and 133; and protein content, 0.02% and 0.03%, respectively. The higher acid number for the lipids of the scutellum was explained by its fourfold content of lipase compared with that of the embryonic axis (Pett, 1935). Other lipid characteristics were almost the same for lipids extracted from both the scutellum and the embryonic axis.

4. Minerals

Good agreement in the values (range 4.30 to 6.72%) for the ash content of hand-dissected germ was reported by Kazakov (1947), Morris et al. (1946), Mambish (1953), and Hinton (1959). Grischenko (1935), however, reported slightly lower values of 3.70 to 4.35% by using an indirect method of dry separation and calculation. Hinton (1959, 1962) found that the ash in the germ accounted for 8.3 to 14.5% of the total ash in Thatcher, Vilmoria, Argentinian, Egyptian, and Australian (soft white) varieties of wheat.

Hinton (1959, 1962) found a 40 to 7% greater concentration of ash in the scutellum than in the embryonic axis of five varieties of wheat. The ash values ranged between 3.51 and 5.36% for the scutellum and between 5.87 and 8.20% for the embryonic axis. Girard and Fleurent (1899) reported 5.45% of ash in the scutellum.

The literature on the mineral constituents of dissected germ is very scanty, and values are available only for phosphorus and manganese. Hinton (1944) reported 1.9% total phosphorus in the scutellum, of which 1.3% was phytic phosphorus, whereas the embryonic axis contained 1.16% total phosphorus, of which only 0.39% was phytic phosphorus. Thus the scutellum contained more than three times as much phytic phosphorus as did the embryonic axis. Pringle (1952) reported similar values for total phosphorus and phytic phosphorus in the scutellum as well as in the embryonic axis. The scutellum and the embryonic

208 S . R. SHURPALEKAR AND P. HARIDAS RAO

axis have been reported to contain 178 and 134 ppm of manganese, respectively (Hinton, 1944).

5. Vitamins

Proportions of certain B-group vitamins determincd by Hinton et al. (1953) in germ fractions are given in Table IX.

a. Thiamine. Ward (1 943) and Fournier (1 946) reported values of 2.03 and 1.35 mg% of thiamine in the embryonic axis and 15.7 and 17.4 mg% in the scutellum, respectively. Hinton (1944) reported similar values of 18 mg% of thiamine in the scutellum and 1.24 mg% in the embryonic axis of germ dissected from eleven varieties of wheat. No significant difference was observed in the thiamine content of the plumule (0.9 mg%) and the radicle (0.72 mg%). A high concentration of thiamine has been reported in the scutellum of durum wheat as compared with the lowest concentration in soft English wheat.

It is evident that the thiamine of wheat is mostly concentrated in the scutellum. Although the scutellum constituted only 1.5% of the kernel weight, it contributed about 60% of the total thiamine in wheat, while the embryonic axis contributed only 3%.

Hinton (1944) also observed no appreciable change in the thiamine content of the scutellum during germination (Table X) or soaking (Table XI) of the wheat kernel. During soaking, however, movement of thiamine to other parts of the kernel was observed only when its cells were made permeable by the action of acid or chloroform.

b. Riboflavin. The germ accounted for about 26% of the riboflavin of the whole wheat kernel. For the Thatcher variety, the embryonic axis of the germ contained 13.8 pglgm, while the scutellum had 12.7 gg/gm (Hinton et al., 1953).

c. Niacin. The niacin contents of the scutellum and the embryonic axis accounted for only 1% of the total niacin content of the Thatcher and English varieties (Heathcote et al., 1952). The values for these varieties as determined by the microbiological method were 38.5 and 5 2 &gm of the scutellum and 38.2 and 38.0 pg/gm of the embryonic axis, respectively.

TABLE IX DISTRIBUTION OF B-GROUP VITAMINS IN WHEAT GERM'

As % o f that in whole grain

Germ fraction Thiamine Riboflavin Niacin Pyridoxine Pantothenic acid

Embryonic axis 2.0 12.0 1.0 8.6 3.5 Scutellum 62.5 14.0 1.3 11.6 4.0

'Hinton ef a[. ( 1 953).

WHEAT GERM 209

TABLE X

EFFECT OF GERMINATION PERIOD ON THIAMINE CONTENT O F

sc u T E L L u M‘

Germination period Th iami ne (days) Condition of seed (Iu/gm)’

- 53 First root just visible 50

45 25

First root 1 cm long First root 3-5 cm long

‘Hinton (1944). ’On a dry-weight basis.

d. Pyridoxine. Clegg and Hinton (1958) determined the pyridoxine content in the structural parts of Thatcher wheat by a microbiological method using Saccharomyces carlsbergensis 4228 as the test organism. They reported 2 1.1 pg/gm in the embryonic axis and 23.2 pg/gm in the scutellum. The aleurone layer, the scutellum, and the embryonic axis contained higher concentrations of pyridoxine compared with other structural parts of wheat grain.

e. Pantofhenic Acid. The contribution of pantothenic acid in the germ was only about 7.5% of the total in the kernel. Pantothenic acid contents as reported by Hinton ef al. (1953) were 14.1 pg/gm of the scutellum and 17.1 pg/gm of the embryonic axis.

TABLE XI EFFECT OF SOAKING ON THIAMINE CONTENT O F SCUTELLUM

Time of soaking Thiamine (hours) (Iu/gm)’

0 1 3 6

12

54 53 4 1 54 54

‘Hinton (1944). ’On a dry-weight basis.

6. Enzymes

Being embryonic in nature, wheat germ contains several enzymes. However, very few data are available on the enzymes of the dissected germ and its structural parts.


a. Dipeptidase, Proteinase, arid Lipase. Pett (1935) determined activities of dipeptidase, proteinase, and lipase in various structural parts of Manitoba hard red spring wheat. The values given in Table XI1 indicate that the scutellum contains higher dipeptidase and proteinase activity than the embryonic axis. The lipase activity was considerably higher in the scutellum, which could be explained by its high f a t content. In contrast to these observations, Engel (1945) found no significant difference in the values for lipase, proteinase, and dipeptidase in both the embryonic axis and the scutellum. This variation was attributed to the difference in the techniques adopted for preparation of the germ components. Engel and Heins (1947) reported 0.8 to 1.3 units of proteinase activity in the germ, and observed that the germ was particularly rich in dipep tidase.

Pett (1935) also observed that both dipeptidase and proteinase activity in the scutellum and the embryonic axis greatly increased after a germination period of 12 hours. This increase was somewhat greater in the cotyledon than in the radicle portion. The activity of enzymes in the embryonic portion decreased rapidly after germination for 12 hours. In the scutellum, however, i t continued to increase only up to 36 hours of germination. The increase in the activity was reported to be due to the change in the germ from a dormant to an active condition. Unlike dipeptidase and proteinase, the lipase activity of the scutellum dropped suddenly during germination. In contrast, the activity in the cotyledon portion increased during the 12-hour germination period and dropped suddenly thereafter. The activity in the radicle, however, did not show any appreciable change during the 36-hour germination period.

b. Lipoxidase, Amylase, Phosphornonoesteruse, Phytase, arid Dehydro- ascorbic Acid Reductase. By the carotene oxidation method, Blain and Todd (1955) reported almost equal lipoxidase activities of 64 and 62 units (defined as the amount required to destroy 0.01 5 mg of carotene in 5 minutes at 20°C) in

TABLE XI1 DII’EPTIDASE, PKOTEINASE, AND LIPASE ACTIVITIES‘ OF

WHEAT GERM C O M P O N E N T S ~

Embryonic axis

Enzyme Scutellum Cotyledon Radicle

Dipeptidase activity 17.1 11.3 20.7 Proteinase activity 17.8 15.8 11.8 Lipase activity 7.3 2.0 0.5

‘Expressed as microliters of 0.05 N HCl per milligram of dry material

bPett (1935). at 40°C.

WHEAT GERM 21 1

the scutellum and embryonic portions of the germ, respectively. According to Engel (1945), the scutellum had 88 units (milligrams of maltose per hour per cubic millimeter of tissue at 40°C) of amylase activity, whereas the embryonic axis had no activity.

Hinton (1 944) found a higher phosphomonoesterase activity in the scutellum (58 King Armstrong units) than in the embryonic axis (36 units) of germ from eleven varieties of wheat. The scutellum of soft wheat (Cuppell deprez) had a high phytase activity of 31.8 units (micrograms of phosphorus per hour per milligram), whereas the embryonic axis had an activity of only 9.0 units (Peers, 1953). However, both the scutellum and the embryonic axis had the same dehydroascorbic acid reductase activity of about 70 units (micrograms of ascorbic acid formed per milligram during 10 minutes at 25"C), as reported by Carter and Pace (1964). It may therefore be concluded that the enzyme activities are more concentrated in the scutellum than in the embryonic axis.

B. MILLGERM

Unlike dissected germ, the composition of mill germ has been studied in great detail by several workers. This may be partly attributed to the ready availability of mill germ from the commercial roller flour mills. Most of the commercial germ contains some bran and endosperm as impurities. It has also been reported that mill germ lacks some of the scutellum components. Thus, mill germ is probably less representative of a single structural part than other mill products like bran and flour. However, some of the studies carried out have been on the composition of the germ in more or less purified form.

I . Proximate Composition

The considerable variation observed in the proximate composition of mill germ is due mainly to different degrees of contamination with bran as well as endosperm. The normal ranges of the proximate composition of commercial samples of mill germ, as reported by Richardson (1884), Grewe and LeClerc (1943), Kent-Jones and Amos (1967), and Farrel et ul. (1967), are given in Table XIII. Grewe and LeClerc (1943) observed that the moisture content of about 9% for the germ was lower than that (13%) of the flour and enhanced the keeping quality of the germ. Lower values (5.2%) of fat indicated contamination of the germ with flour. The germs from hard red spring and durum wheat had appreciably higher fat and protein contents than did the germ from soft wheats.

Carbohydrates present in commercial germ could be the best index of purity for most of the germ samples. The carbohydrates in germ fractions from hard red spring and durum wheats were the lowest (24.3%), compared with 30.4% for hard red winter, 36% for white wheat, and 39% for soft red winter wheat. These


TABLE XI11 PROXIMATE COMPOSITION O F COMMERCIAL GERM

Constituent (%I

. -

Moisture Protein (N X 6.25) Ether extractives Mineral matter (total ash) Cellulose (fiber) Carbohydrate (by difference) Starch

Farrel er ~ 1 . ~ Kent-Jones and Amos Grewe and LeClercb (1943)

~

(1967) (1967)

Range Range Range Average (%) (70) (%) (%)

11.3-12.9 9.0-13.0 7.4-11.5 9.2 21 .I-24.5 22.0-32.0 18.3-35.3 28.9

6.5-10.6 6.0-11.0 5.2-15.0 9.7 3.5- 4.3 4.0- 5.0 3.1- 4.9 4.1 2.4- 4.0

~ 35.045.0 19.2-53.0 30.4

. _ - _ ~

1.8- 2.5 - -

14.Ck23.9 - - -

Richardson (1884)

Average (%)

8.4 30.1 12.5 4.6

44.4 -

uValues for germ obtained from nine varieties of wheat. b a l u e s for nineteen samples of commercial germ representing five classes of American

wheat.

observations indicated that the flour portion of the germ processed from hard wheats could be easily separated owing to its granular nature as compared with that of soft wheat germ.

Fraser and Holmes (1 959) determined the comparative proximate composition (Table XIV) of commercial samples of flour, germ, and bran. The data indicated that the germ contains three times as much protein, seven times as much fat, six times as much ash, and about fifteen times as much sugar as does endosperm flour. Unlike others, these workers have reported the carbohydrate values for different fractions individually and not by difference. It is interesting to note that, compared with other mill products, sugars form the major fraction of the germ carbohydrates. Booth et al. ( 1 941) reported somewhat similar values for all three fractions obtained during the actual milling process. However, the protein content of the germ was only twice that of the endosperm. This variation could be attributed to the purity of the germ and the variety of wheat from which the germ was obtained.

In recent years, there have been vast innovations in the flour milling techniques involving heavy feeding of the rolls, reduction in the roller surface area, a shortened milling system, etc. (Jones, 1964). Kent-Jones and Amos (1 967) analyzed the different fractions milled in the improvised flour mill (Table XIV).

To summarize, there is considerable variation in the literature values reported for the proximate composition of the germ and its fractions. However, the values reported recently by Farrel et al. (1967) for germ milled from nine varieties of wheat can be taken as the best representative values for normal samples (Table XIII) .

WHEAT GERM 213

TABLE XIV PROXIMATE COMPOSITION OF COMMERCIAL M I L L P R O D U C T S ~

Composition (%)

Endosperm Germ Bran

Constituents Ka F b Ka Fb Ka Fb

Moisture Protein (N X 5.7) Fat Ash Carbohydrate (by difference) Starch Hemicellulose Sugar Cellulose Total carbohydrate Recovery of fraction

14.7 11.3 0.8 0.4

72.8

14.0 9.6 1.4 0.7

74.3 71.0

1.8 1.1 0.2

74.1 99.8

12.6 29.8 10.6 4.7

41.1 -

11.7 28.5 10.4 4.5

44.9 14.0 6.8

16.2 7.5

44.5 99.0

~~ ~~

12.6 13.2 13.6 14.4 2.8 4.7 5.9 6.3

66.3 61.4 - 8.6 - 26.2 - 4.6 - 21.4 - 60.8 - 99.4

‘Kent-Jones and Amos (1967). bFraser and Holmes (1959).

2. Protein

a. Conversion Factor for Germ Protein. A factor of 6.25 is being used normally to convert the total nitrogen of the germ into protein even though it was considered high by Jones (1931) and Tkachuk (1969). Jones obtained a conversion factor of 5.8 by taking into consideration the fact that different plant proteins contained various amounts of nitrogen. Later, Tkachuk (1969) reported a conversion factor of 5.45 based on the amino acid content of the germ. This low value reflected the substantial amount of nonprotein nitrogen present in the germ.

b. Protein Content. The protein content (N X 6.25) of mill germ has been reported to vary from 18.3 to 36.7% (Richardson, 1884; Jacobs and Rask, 1920; Sullivan and Bailey, 1936a; Booth et al., 1941; Grewe and LeClerc, 1943; Fraser and Holmes, 1959; Kent-Jones and Amos, 1967; Waggle etal., 1967). This wide variation probably reflects on the amount of contamination of the germ as well on as the variety of wheat milled.

c. Protein Fractions. Types of protein in wheat germ fractionated according to their solubility characteristics were entirely different from those of flour proteins. There is no literature available to prove the presence of a gluten type of protein in the germ as exists in flour. Protein fractions of mill germ were first reported as percentages of the total protein by Osborne (1907): albumin, 30.2; globulin, 18.9; gliadin, 14.0; glutenin, 0.3 to 0.37; and insoluble, 30.2. Danielson


TABLE XV RELATIVE FRACTIONS OF TOTAL NITROGEN IN WHEAT GERM SAMPLES OF

HIGH A N D LOW CARBOHYDRATE C O N T E N T S ~

Relative fraction of total N -~

70% 3% 5% N not alcohol- NaCI- K, SO,- Cu(OH), precipitated by

Total soluble soluble soluble precipitated phosphotungstic Glutenin Sample N N N N N acid NtJ

-~ ~~ .~ ~~

Germ high in 4.3 15.4 63.8 55.9 92.0 13.6 28.7 carbohydrates (40.8%)'

carbohydrates (24.4%)'

Germ low in 5 7 12.6 65.7 58.2 88.8 14.0 29.2

Individual resultsd 5 .1 13.9 65.1 57.0 90.2 13.7 29.1 Wheat flour 2.3 52.6 24.1 14.7 95.7 3.5 32.2

( fo r comparison)e

'Grewe and LeClerc ( 1 943). bTotal N - (5% K, SO, -soluble N + 70% alcohol-soluble N). 'Average for eight samples. dAverage for nineteen samples. eAvcrage lor four samples.

( 1 949) reported two distinct fractions-alpha and gamma globulins-in wheat germ on the basis of their sedimentation behavior in the ultracentrifuge. How- ever, Pence and Elder (1953) later showed the presence of a third component- delta globulin-in defatted wheat germ.

The nitrogen fractions of nineteen samples of germ determined by Grewe and LRClerc (1943) showed the presence of a high proportion of salt-soluble proteins-albumin and globulin-which accounted for nearly 60% of the total nitrogen (Table XV); in flour they accounted for only about 15%. However, germ protein contained only about 15% of alcohol (70%)-soluble nitrogen, which in the case of flour protein accounted for more than half of the total protein.

Pomeranz ef al. (1970a) found that the solubility of germ proteins depended on the drying temperature and concentration of the salt solution used for extraction. The extraction of protein in 0.02 N acetic acid decreased from 32.6% to 1.1% when the drying temperature was increased from 70°C to 130°C. A 3% sodium chloride or calcium chloride solution yielded as high as 83% protein in the extract on a dry basis.

The starch gel electrophoresis pattern of gluten and germ proteins showed that the gluten protein was completely absent in the germ extract (Pomeranz e l al.,

WHEAT GERM 215

1970a). The germ protein contained a wide spectrum of fast-moving, salt-soluble proteins, separated into several bands. The most prominent band was somewhat reduced in the sodium chloride extract. This band was much smaller in the high-protein air-classified fraction than in the low-protein one (Fig. 7).

From wheat germ Johns and Butler (1962) obtained histones which, unlike the histones of animal tissues, had a higher total lysine content.

d. Nonprotein Nitrogen. Wheat germ contained high amounts of nonprotein nitrogen ranging from 11.3 to 15.3% (Osborne, 1907; Grewe and LeClerc, 1943). According to Bailey (1 944) this nitrogen included mainly asparagine,

1 2 3 4 5 6

Water and salt-soluble proteins.

FIG. 7 . Starch-gel electrophoretic patterns (migration from slots on top of figure) Of

proteins in ( 1 ) whole germ, (2) wheat flour gluten, (3 ) germ air-fractionated low-proteh fraction, (4) germ air-fractionated high-protein fraction, (5) NaCl extract of g e m proteins, and (6) whole germ.


TABLE XVI NONPROTEIN NITROGEN COMPOUNDS OF GERM

~ ~~ ~ ~~

Nitrogen compound Quantity ‘ References

Asparagine (as total amide N) (lo) Allantoin (as total amidc N) (lo) Betdine (%) 0.306-0.604’ Choline (mg/grn) 2.59 -3.306

0.53 0.70

3.00 -2.90 3.04

Lecithin (70) 1.25 Glutathionc (5%) 0.35

0.46

‘On a 14% moisture basis. ’Range of values for nine samples of gcrm.

Teller and Teller (1932) Frankfurt (1 896) Waggle et al. (1967) Waggle ef al. ( 1 967) Engel (1943) Glick (1945) Geoffroy (1934) Albizatti (1937) Sullivan et al. ( 1 9 3 6 ~ ) ; Sullivan

and Howe (1937)

betaine, choline, lecithin, allantoin, glutathione, and arginine. Engel (1943) reported higher values of choline in defatted germ than in raw wheat germ. This finding was later discredited by Glick (1945), since practically most of the choline exists in the form of lecithin. Sullivan et al. ( 1 9 3 6 ~ ) reported 0.46% of glutathione (Table XVI) in freshly prepared germ, as determined by Weller’s method (1935). Later Howe et al. (1937) obtained 0.1 to 0.2 gm of almost pure glutathione from 2 kg of germ. Wasserman and Burris (1965) isolated hemoprotein from the germ and resolved a major component, WCHP550 (wheat germ hemoprotein SSO), by chromatography. Uroma and Louhivuori (1 954) found that the HC1-acetone-extracted protein fraction, when injected, decreased the eosinophile count in the peripheral blood of rats.

3. Amino Acids

The literature values for the amino acid composition of the germ and germ proteins show wide variation. Such variation is attributed mainly to the methodology followed for estimation, the purity of the germ, and the variety of wheat used. Most of the published literature values have been obtained by microbiological methods. In recent years, the automatic ion-exchange chromatographic method has been used because of its simplicity and rapidity as compared with the microbiological method. The main difficulties encountered in different methods of estimation occurred during hydrolysis with 6 N HCI at 1 10°C for 24 hours (Hires et al., 1954), since the rate of stability and the rate of release varied widely for different amino acids. The amino acids serine, threonine, cystine, and methionine were found to be unstable, while valine and isoleucine were released slowly during hydrolysis (Rees, 1946; Tkachuk and Irvine, 1969). This problem

TABLE XVII: AMINO ACID COMPOSITION^ OF MILL GERM PROTEIN

Hepburn et al. Barton-Wright Block Block (1960)b Kohler Tkachuk

and and Horn and Lyman and and Miladi Moran Mitchell (1949, Dunn Dunn Bollingf et al. Mill Mill Palter lrvine et al.

Amino acid (1946)b (1946)‘ 1950)b (1950)b.d (1950)b*e (1951) (1956)b A B (1967)g (1969)g (1972)g

Alanine Arginine Aspartic acid Cystine Clutamic acid Clycine Histidine Isoleucine Leucine Lysine Methionine Phenyldanine Proline Serine Threonine Tyrosine Tryptophan Valine Total nitrogen

(dry basis) Recovery (%)

-

6.20

1.37 -

-

- 3.03 5.23 7.33 5.44 1.28 2.47 - -

6.28

0.90 4.20 5.22

-

-

- - 6.0 6.9

0.8 - - -

- - - -

2.5 2.1 - 3.6

6.7 6.0 5.5 6.2 - 1.3

4.2 3.5 - - - -

3.8 4.0 3.8 - 1.0 0.7 - 4.8 - -

- -

-

5.4 - -

13.0 5.7 2.1 3.7 6.0 5.1 1.2 2.5 -

-

-

-

- 4.4 -

-

- 5.4 - -

16.0 5.2 2.3 4.1 5.9 4.3 1.3 3.0 -

- - -

- 4.8 -

-

- - 5.23 5.08 6.0 7.41 6.88 7.04 - - 7.48 7.19 1.1 - 1.04 1.19 - - 14.00 17.30 - - 5.22 4.94 2.4 2.28 2.26 2.08 3.9 3.45 3.48 3.28 6.7 5.95 5.75 5.72 5.5 6.55 5.28 4.78 1.4 1.64 1.91 1.73 3.1 3.90 3.38 3.68

5.03 6.09 - - 4.60 4.60

5.0 3.95 3.42 3.44 3.8 2.95 - - 1.0 1.07 - - 4.8 5.02 - -

- 4.51 4.63 4.40

- -

5.68 5.7 7.36 7.5 7.67 8.1 1.66 1.4

15.30 13.3 5.47 5.4 2.38 2.3 3.58 3.1 6.12 5.6 5.25 6.2 2.26 1.6 3.67 3.1 4.71 3.7 4.24 4.3 3.74 3.8 2.72 2.4 - I .4

5.25 5.5 4.52 6.25

88.00 83.10

5.21 6.93 7.30 1.88

17.13 5.39 2.38 3.68 6.04 4.92 1.89 3.78 5.23 4.22 3.52 2.58 1.28 5.22 4.45

89.20

“Grams per 16 gm of nitrogen. bMicrobiological method. fPaper chromatographic method. ‘Chemical method. gIon-exchange chromatographic method. dDefatted.

eDefatted and toasted.


has been overcome by applying suitable correction factors or by converting the unstable amino acids (cystine and methionine) to a more stable form (Schram el GI., 1954). Tkachuk and Irvine (1969) obtained the following correction factors: threonine, 1.07; serine, 1.06; valine, 1.01 ; and isoleucine, I .05.

The amino acids of germ proteins and the germ are given in Tables XVII and XVIII , respectively. The values reported by Block and Mitchell (1946) by chemical methods were somewhat different from those determined by the niicrobiological method. This may partly bc due to varietal differences of wheat. Isoleucine and leucine were difficult to estimate by chemical methods, as no satisfactory method of separation was available. Barton-Wright and Moran (1946) observed that the sum of the isoleucine and leucine values was almost the same by both chemical and microbiological methods. Most of the amino acid values reported by Tkachuk and lrvine (1969) are higher than other reported values, as they were determined in pure commercial germ free from bran.

TABLE XVIII A M I N O ACII) COMPOSITION O F GERM'

Amino acid __ ___~.

Alanine Argininc Aspartic acid Cystine Glutamic acid Glycinc Histidine I soleuc ine Leucine Lysinc Methionine Phen ylalamine Prolinc Scrine Threoninc Tryptophan Tyrosinc Valinc

Whggle et al. (1967)b

- - ~ -

1.34-1.7 1 1.77-2.09 1.92-2.2s 0.43-0.61 3 .654 .59 1.32-1.58 0.59-0.82 0.77-0.94 1 .SO-1.75 1.30-1.77 0.39-0.58 0.86-1 .0 I I . 13-1 .52 1.05-1.28 0.89-1.09

-

0.65-0.78 1.01 -1.37

Andrews and l e l t (1941)

cited in MacMasters et al. (1971)'

1.30 1.71 1.86 0.26 3.48 1.30 0.56 0.84 1.43 1.31 0.47 0.84 1.25 1.11 0.85 2.44 0.71 1.23

_ _ ~ ~~~~

Barton-Wright Horn ef al.' and Moran (1946, 1947a,b,c,

(1946)' 1948a.b. 1949a.b)

0.50 -

- -

- -

0.70 0.72 1.91 1.27 2.66 2.10 1.99 2.17 0.46 0.44 0.90 -

- -

2.29 1.40 0.31 -

1.52 1.68 - -

'Crams per 100 gm of germ on a 14% moisture basis. bChromatograpliic determination, range of nine wheats. 'Microbiological determination.

WHEAT GERM 21 9

TABLE XIX AMINO ACID COMPOSITION" OF WHEAT FLOUR, GLUTEN, AND DEFATTED GERM

OR GERM P R O D U C T S ~ ~~~ ~ _ _ _ _ _ _ _

Air-classified germ

Whole NaCl extract High-protein Low-protein Amino acid Flour Gluten germ of germ fraction fraction

Lysine 1.78 Histidine 1.82 Ammonia 3.01 Arginine 3.23 Aspartic acid 3.81 Threonine 2.31 Serine 4.43 Glutamic acid 37.19 Proline 11.55

Alanine 2.87 Cystine 1.44 Valine 3.99 Me thionine 1.45 Isoleucine 3.80 Leucine 6.64 Tyrosine 2.15 Phenylalanine 5.16

Glycine 3.37

1.53 1.77 3.33 3.14 3.05 2.36 4.18

39.30 11.49 3.03 2.37 1.61 3.58 1.45 3.5 1 6.31 3.30 4.68

7.76 2.65 1.71 8.86

10.21 4.82 4.62

15.45 4.37 6.54 7.00 0.66 5.65 1.88 3.91 6.79 3.12 4.07

8.33 2.58 1.54 9.85 8.81 4.92 4.64

15.94 4.04 6.95 6.89 0.88 5.5 1 2.11 3.59 6.37 3.26 3.86

6.41 3.35 2.26

10.60 9.67 4.27 4.10

16.47 4.22 6.58 6.40 0.75 5.80 1.77 3.64 6.53 3.02 4.20

7.30 2.40 3.15 7.27 9.58 4.40 4.60

16.76 5.07 6.34 6.70 1.09 5.06 1.89 3.61 7.45 3.34 4.02

'Crams per 100 gm of amino acids. bpomeranz et UZ. (1970a).

The amino acid contents of various mill fractions were reported by several workers and in recent years by Hepburn et al. (1960), Waggle et al. (1967), and Kohler and Rhoda (1967). It was found that the germ contained the highest amount of essential amino acids as compared with other milled products. The germ was also rich in the essential amino acids lysine, methionine, and threonine, in which many of the cereals are deficient.

Pomeranz et al. (1970a) determined the amino acid content of defatted germ, flour, gluten, salt extract of germ, and air-classified fractions of germ containing high- and low-protein fractions by the ion-exchange chromatographic method. The values reported are given in Table XIX. The amino acid composition of germ protein, which agreed well with the literature values, differed significantly from that of flour proteins or gluten. However, the amino acid composition of both defatted germ protein and the sodium chloride-extracted protein did not show any significant difference. The values for the amino acids lysine, serine, proline, alanine, leucine, and tyrosine, and the sulfur-containing amino acids


were higher in the low-protein air-classified fraction than in the high-protein fraction.

4. Nucleic Acid

The values reported by Osborne and Harris (1902) and by Javillier and Colin (1933) for the ribonucleic acid (RNA) content of the germ were 3.5% and 4.2%, respectively. The purity and yield of RNA was low when either of the methods described by Osborne and Harris (1902) or by Clark and Schryver (1917) were used. The composition of RNA as reported by Osborne (1907) and Osborne and Hey1 (1908) was similar to that of RNA present in yeast (Calvery and Remson, 1927; Jones and Perkins, 1925; Levene and Bass, 1931; Read and Tottingham, 191 7). Lusena (1951) described a method for purification of RNA and isolated 0.8% of RNA of 99% purity from wheat germ. Lipshitz and Chargaff (1956) isolated, purified, and analyzed deoxyribonucleoprotein and deoxyribonucleic acid from wheat germ.

5. Lipids

a. variation in Lipid Content. Wheat germ contains a high percentage of fat compared with other mill products like bran, patent flour, and shorts. The values reported for lipid contents of mill germ are given in Table XX. The wide variation in these values is attributed to the following reasons:

Method of solvent extraction. Herd and Amos (1 930) observed a higher vahe for lipids obtained by hydrolysis as compared with direct extraction with petroleum ether (Table XX). Higher values were attributed to the extraction of bound lipids, whereas ether extracted more or less free lipids.

TABLE XX LIPID CONTENT O F MILL GERM

Quantity (70)

Lipid Range Average References

Ether extract 5.05-18.90 9.45 Ball (1926); Barton-Wright (1938); Grewe and LcClerc (1943);Herd and Amos (1930); Sullivan and Near (1928, 1933); Sullivan and Bailey (1936a)

Alcohol extract 7.70-14.14 10.75 Barton-Wright (1938); Channon-Foster (1934) ; Herd and Amos (1930); Sullivan and Near (1928, 1933); Sullivan and Bailey (1936a)

Acid hydrolysis - 8.27 Herd and Amos (1930)

WHEAT GERM 22 1

Purity of germ lipids. Herd and Amos (1 930) and Sullivan and Near (1 933) estimated the nitrogen and phosphorus contents in the lipid material obtained by different extraction procedures. The data (Table XXI) indicated that direct extraction and acid hydrolysis gave a product more or less free from nitrogen and phosphorus compared with that obtained by alcohol hydrolysis methods. The high values for nitrogen and phosphorus in lipids obtained by alcohol hydrolysis were attributed to the presence of other lipoid materials such as sterols and pigments. Similarly, Sullivan and Near (1 933) found minimum and maximum contamination with nitrogen and phosphorus in ether and alcohol- ether extractives, respectively.

Variety of wheat. Using the same solvent and extraction procedure, Grewe and LeClerc (1943) reported a range of 5.0 to 15.0% for ether extractives in nineteen samples of commercial germ milled from five varieties of American wheats. The average maximum and minimum lipid contents were found in the germs obtained from durum wheat and soft wheat, respectively. The purity of the germ also contributed considerably to the variation in the lipid contents.

b. Composition of Lipids. The composition of germ lipids was extensively studies by Nelson er QZ. (1963a, b), Moruzzi er al. (1969), and Pomeranz er aL (1970a). Different constituents of germ lipids reported by Moruzzi et al. (1969) are given in Tables XXlI and XXIII. Nelson er al. (1963a) separated and identified four lipid fractions from germ, bran, and endosperm by column chromatography (Table XXIV) and showed that more than 74% of lipids of bran and germ were nonpolar (tri-, di-, and monoglycerides, fatty acids, sterols) and less than 25% consisted of polar lipids (phospho- and glycolipids). In contrast, endosperm lipids contained more than 50% of polar lipids and 47% of nonpolar lipids. However, Moruzzi et al. (1969), by extracting the germ lipids according to

TABLE XXl

LIPID CONTENT O F GERM A N D ITS PURITY AS AFFECTED BY

VARIOUS METHODS O F EXTRACTION'

- Methods

Soxhlet extraction Petroleum ether Ethyl ether

Hydrolysis Alkali Acid Alcohol

Lipid content Nitrogen Phosphorus (%) (%.) (%o)

- 7.82 -

8.26 0.08 0.28

8.80 0.16 0.53 9.62 0.16 0.15

10.31 0.43 0.48

'Herd and Amos (1930).

TABLE X X l I

LII'II) CONSTITUENTS O F WHEAT GERM'

Total lipids Phospholipidsb Glycolipidsc Neutral fat" Protein Amino nitrogen

Total I- rcc

Lipid constituent (9)

100.00 1.38 0.75

96.21 1.66

0.10 0.01

Mg %. of germ

9380 130 71

9024 155

13 0.99

'Moruzzi et nl . ( 1 969). bMilligrams (if lipid phospliorus X 25. 'Galactose x 4.55. dTotal lipid - (phospholipids + plycolipids + protein).

TABLE XXIIl

L I P I D CONSTITUENTS or: GEKM'

Lipid cons t it ucnt

Neutral fat Sterol esters Triglyceridcs and free fatty acids Mono- and diglycerides Polar lipids containing phosphorus Phosphatidyl cholineb Noncholine nonethanolamincb Phosphatidyl etli;inolamineb ~ ~ i o s p ~ i a t i d y ~ serincb Phosphntidic acid, etc. Polar lipids containing galactosc Protcins of proteolipids

Pcrcent of germ ~~

9.02 0.56 6.10 2.40 0.130 0.052 0.0091 0.0 I29 0.0032 0.053 0.071 0.1558

'Moruzzi et al. (1969). bl:scluding phosphatidic acid.

TABLE XXIV L I P I D FRACTIONS O F W A N , G E R M , A N D ENDOSPEKM'

Lipid fraction Bran Germ Endosperm (%) (%I (%)

Hydrocarbon and stearyl esters 0.5 3.7 Traces Triglyceridcs 56. I 57.0 29.9 I"atty acids, sterols, mono- and diglycerides 25.1 17.8 17.1 Phospholipids and glycolipids 22.5 16.5 52.4

Total 104.2 95.0 98.9

__ .....

'Nelson ct al . (1963a).

WHEAT GERM 223

TABLE XXV PHOSPHOLIPIDS A N D GALACTOLIPIDS I N POLAR L I P I D FRACTION O F GERM'

Percent of fraction

Fractions Base found Phospholipids Galactoliuids

Phosphatidyl choline (lecithin) Choline 53.32 23.78 Choline and amino-free phospholipids - 29.25 64.73 Phosphatidyl ethanolamine Et hanolamine 13.01 11.49 Phosphatidyl scrine Serine 4.40 -

'Moruzzi ef 01. (1969).

the method of Brady (1964), found as high as 97% of germ lipids to be nonpolar. This variation may be attributed to the difference in the method followed for extracting lipids from the germ. Further separation of polar lipids into four fractions (Table XXV) showed that lecithin was abundant in the iolar lipid fraction. The different fractions identified in nonpolar lipids are indicated in Fig. 8.

Fractionation of polar and nonpolar lipids by thin-layer chromatography (Pomeranz e l al., 1970a) showed a virtual absence of polar lipids in free lipids of petroleum ether extractives (Fig. 9). However, bound lipids contained small amounts of polar lipids, presumably consisting of phospholipids and some glycolipids. They reported that free and bound lipids were present in the ratio of 12:2.

1 2 3 4 5 6

FIG. 8. Chromatography on silicic acid-impregnated paper of different nonpolar lipid fractions from wheat germ. y = yellow; B = blue fluorescence after staining with Rhodamine 6-G and examination under an ultraviolet lamp. 1 = nonpolar lipids of egg yolk: ( la ) monoglycerides, ( l b ) diglycerides, ( lc ) triglycerides, ( I d ) cholesterol esters; 2 = nonpolar lipids of wheat germ: (2a) monoglycerides, (2b) diglycerides, (2c) triglycerides, (2d) sterol esters + tocopherols; 3 = tocopherol standard; 4 = sterol esters fraction of wheat germ; 5 = triglycerides fraction of wheat germ; 6 = mono- and diglycerides fraction of wheat germ: (6a) monoglycerides, (6b) diglycerides, (6c) tocopherols.


c. Phospholipids. The germ contains a high percentage of phospholipids when compared with other mill fractions (Barton-Wright, 1938). The literature values (Barton-Wright, 1938; Channon and Foster, 1934; Sullivan and Near, 1928, 1933) for phospholipids in the germ range from 0.65 to 4.17%. The analysis of phospholipids reported by Channon and Foster (1934) is given in Table XXVI. Fractionation of phospholipids showed the presence of phosphatidic acid (as salts of calcium, magnesium, and potassium), lecithin, and cephalin in the proportion of 4:4:1 on the basis of their phosphorus content. About 42% of the total phosphatide was phosphatidic acid.

d. Unsaponi@ble Fraction. The unsaponifiable fraction of mill germ which contained sterols, tocopherols, and pigments ranged from 0.32 to 0.80%, with an average of 0.45% (Ball, 1926; Barton-Wright, 1938; Channon and Foster, 1934; Sullivan and Bailey, 1936b). Sullivan and Bailey (1936b) found 4% of germ fat to be unsaponifiable. Of this, 70% was a mixture of sterols, and the remaining 30% consisted of yellow viscous oil, the composition of which was not de-

Nonpolar Polar 1 2 3 4 5 6 1 8

FIG. 9. Thin-layer chromatography of lipids in wheat flour and wheat germ. Samples 1 to 4 fractionated with chloroform, 5 to 8 with chloroform-methanol-water (65:25:4). Samples 1 and 5 free lipids (petroleum ether extract) of flour; 2 and 6, bound lipids (water-saturated butanol extract following petroleum ether) of flour; 3 and 7, free lipids of germ; 4 and 8, bound lipids of germ. Tentatively identified as (A) hydrocarbons and steryl esters, (B) triglycerides, (C) diglycerides, (D) free fatty acids, (E) unresolved polar lipids, (F) unresolved nonpolar lipids, (GI digalactosyldiglycerides, and (H) phosphatidyl choline.

WHEAT GERM 225

TABLE XXVI ANALYSIS OF ACETONE-INSOLUBLE FRACTION OF WHEAT

GERM OIL'

Characteristics Average value

for seven samples

Yield (as % of extract) Yield (as "/o of germ) Iodine value Fatty acids (70) Iodine value of fatty acids Nitrogen (70) Phosphorus (%) Ash (%)

12.8 1.1

77.0 56.2 123.0 1.60 2.65 2.70

'Channon and Foster (1934).

termined. However, preliminary work indicated the presence of polyene hydrocarbons and alcohol. About 56% of the sterol was in the free state; the remaining was in the bound form. Ellis (1918) reported 0.5% of sterol in the germ. Later, sterols were shown to be a mixture of hydrositosterol and four isomeric sitosterols: alpha, beta, gamma (Anderson et aZ., 1926; Ichiba, 1935b), and delta (Ichiba, 1935a). The presence of ergosterol (12 ppm on germ basis) and dihy- droergosterol was reported by Drummond et al. (1 935). Fernholz and MacPhil- lamy (1941) isolated a new phytosterol called campesterol from wheat germ.

e. Fatty Acid Composition. Jamieson and Baughman (1932) and Sullivan and Bailey (1936a) reported that linoleic acid accounted for nearly half of the

TABLE XXVII

FATTY ACID COMPOSITION O F LIPIDS O F WHEAT GERM

Nelson et al. ( I 963b) Moruzzi ef al. (1969)

Fatty acid Total Total Nonpolar Polar (methyl esters) lipids Triglycerides lipids lipids lipids

(%) (%) (%) (%I (%)

Myristate (C-14:O) Trace Palmitate (C- 16: 0) 18.5 Palmitoleate (C-16: I) 0.7 Stearate ((2-18: 0 ) 0.4 Oleate (C-18:l) 17.3 Linolea te (C-18: 2) 57.0 Linolenate (C-18:3) 5.2 Arachidate (C-2O:O) Trace Others 0.8

Trace 19.4 0.8 0.5 19.6 52.5 4.5 0.5 2.4

20.03 0.30 0.30 16.68 56.00 5.05 2.06

19.77 0.58

16.50 58.40 4.61

-

-

18.39 1.74 1.08 19.44 43.49 12.12 4.09

TABLE XXVIII

PHYSICAL A N D CHEMICAL CHARACTERISTICS OF WHEAT GERM LIPIDS

Sullivan and Bailey Channon and Jamieson and Ball Barton-Wright (1938) (1936a) Foster (1934) Baughman (1932) ( 1 926)

Petroleum Acetone-soluble Alcohol-ether Alcohol-ether Ether Characteristics ether extract fraction extract extract extract Ether extract

Specific gravity - -

Refractive index - -

Acid value Saponification value Iodine number Thiocyanogen number Hexabromide number Acetyl value Reichert-Meissel value Polenske number Hehner number Soluble acids as butyric (70) Ester number Unsaponifiable matter (70) Iodine number of

unsaponifiable matter Thiocyanogen number of

unsaponifiable matter

24.57 184.00 127.40 73.48

2.96 -

-

-

- -

-

4.71 -

-

24.40 186.20 130.90

73.52 2.96 -

-

-

-

-

-

5.21 -

-

0.9326 (26"/26") - 0.9268 1.4686 (17'/1°) - 1.4762 (25'/25") 0.9249 (25"/1") 1.4800 (20")

6.95 17.6 184.00 184.0 125.0 (Rosenmund) 111.0 84.7 -

2.28 -

16.7 -

0.77 -

0.44 -

89.00 -

1.44 ~

177.05 -

4.00 7.03

7.6 (20") 186.5 125.6 (Hanus) 79.7

Trace 9.9 0.2 0.35 -

-

- 4.70

97.30

62.30

21.48 184.13 123.64 (Wijs) - -

-

0.475 0.25

93.70

162.65 3.59

-

-

-

Saturated acids (Twitchell) (%)

Saturated acids (Bertram) (%)

Saturated acids (lead salt-ether) (%)

Unsaturated acids (%)

Iodine number of total fatty acids

Thiocyanogen number of total fatty acids

Iodine number of unsaturated fatty acids

Mean molecular weight uf total fatty acids

Mean molecular weight of saturated fatty acids

Mean molecular weight of unsaturated fatty acids

16.0

84.0'

134.10

80.87

160.10

278.00

266.00

309.00

16.0

-

84.0'

132.90

79.64

158.40

278.00

266.00

307.00

16.00

17.87

84.00'

129.90

79.30

153.00

278.00

262.20

281.00

-

120.00

-

-

284.00

-

13.30 (COI.)

75.30 (corr.) -

160.70

-

15.83

84.17'

128.11

145.97

212.72

245.08

276.85

'Percent of total fatty acid determined. 'Percent of total fatty acid calculated.


total fatty acids. The unsaturated fatty acids reported by Sullivan and Bailey (1936a) are:

Total unsaturated fatty acids 84.00% a-Linolenic acid 1.83% 0-Linolenic acid 1.72% a-Linoleic acid 22.32% p-Linoleic acid 29.99% Oleic acid (by difference) 28.14%

Palmitic acid, the principal fatty acid, formed 73.5% of the total saturated fatty acids. Jamieson and Baughman (1932), however, reported a higher value of 91%. The remaining 9% was mostly stearic and lignoceric acids.

Studies by Nelson et al. (1963b) and Moruzzi et al. (1969), using gas-liquid chromatography of methyl esters of fatty acids, presented similar figures with slightly high values for linoleic and low values for oleic acid (Table XXVII). In addition, some new fatty acids were detected in traces. No significant difference was observed in the fatty acid composition of total lipids and triglycerides except for the higher values of linoleate in the total lipids. Myristate and arachidate were the new fatty acids found in traces in the germ. The fatty acid composition of nonpolar lipids was somewhat different, when compared with that of polar lipids. Nonpolar lipids contained more of linoleate and less of linolinate and oleate. f: Constants of Wheat G e m Oil. The physical and chemical constants of

wheat germ oil were reported in the early 1930’s by several workers (Table XXVIII). Many of the constants reported were somewhat similar except for slight variations caused by differences in the me thodology followed for determination. The specific gravity of germ oil was quite normal. The saponification value was comparable to the normal value for vegetable oils. Because of the high iodine value, germ oil was classified among the semidrying oils (Lewko- witsch, 1915). The germ oil had a higher saponification value as well as iodine number, a lower specific gravity, and contained more of the unsaponifiable fraction when compared with flour oil.

Ball (1926) found very little difference in the specific gravity of germ oil obtained by ether extraction and extraction under pressure. The iodine value, however, was slightly higher in pressure-extracted oil.

The characteristics of Bulgarian wheat germ oil as compared with three commercial samples of imported germ oil have been reviewed by Ivanova et al.

Ivanova and Popov (1 974) have compared the characteristics of laboratory-extracted oil from fresh wheat (variety Bezostaia) germ with germ oils extracted (i) commercially, (ii) by pressure, and (iii) by extraction.

( 1974).

WHEAT GERM 229

TABLE XXIX EFFECT OF DRYING ON WEIGHT OF GERM LIPIDS‘

(ON DRY BASIS)

Conditions of drying

24 h r i n 48 h r i n 2 h r a t 15 h r a t 21 h r a t desiccator desiccator 98°C 98°C 98°C

Solvent used (gm) (gm) (gm) (sm) (gm)

Ethyl ether 8.40 8.40 8.26 8.26 8.26 Petroleum ether 7.87 7.85 7.82 7.75 7.75

‘Herd and Amos (1930).

The effects of drying under different conditions on the weight and physical constants of germ oil were studied by Herd and Amos (1930). They reported that the weight of ether-extracted germ lipids was constant even after 24 hours of drying in a vacuum desiccator. Very little loss in weight was observed during the first 2 hours of heating at 98°C. Thereafter, the weight remained constant even after heating for 21 hours (Table XXIX). Even though the weight was constant after 2 hours of drying, the physical constants changed slowly, even beyond the 2-hour period (Table XXX). Bromine values and iodine values decreased as the time of heating increased, and specific gravity increased only slightly. No appreciable difference was observed in the constants of germ oil obtained by using different solvents.

g. Stability of Germ Oil. During 30 days of storage of laboratory extracted oil in the dark, Ivanova and Popov (1974) observed that the acidity index of the

TABLE XXX EFFECT O F DRYING ON THE PHYSICAL CONSTANTS O F GERM OIL‘

Condition of drying

Air drying 24 hr in desiccator 48 hr in desiccator 12 hr at 98°C 18 hr at 98°C 36 hr at 98°C

Solvent used

Ethyl ether Petroleum ether

Specific gravity Bromine Iodine (NDzo ) value value

1.470 - -

1.479 81.8 129.9 1.479 81.3 129.1

1.480 73.3 116.4 - - -

Specific gravity (ND”)

-

1.480 1.479 1.485

1.488 -

Bromine value

- 81.5 - - -

61.5

‘Herd and Amos (1930).


oil increased from 5.27 t o 17.82 and the peroxide index from 0 to 0.08 a t ambient temperature, but remained unchanged at 4°C. Further, they observed that resistance of germ oil to autooxidation was double (12.7 hours) that of sunflower oil (6.2 hours) in a modified Schaal oven test at 100°C.

6. Carbohydratrs

Generally, the carbohydrate content of any food is calculated by difference. Thc carbohydrate content of mill germ varies widely (19.2 to 53.0%; see Table XIII), depending o n the contamination with the endosperm and bran portions (Grewe and LeClerc, 1943). It is, therefore, the best index of purity of mill germ.

a. Carbohydrate. Composition. Fraser and Holmes (1 959) found hemicellulose, cellulose, starch, and sugars as the carbohydrate fractions of mill germ (Table XXXI). Sugars formed the major component of the germ, while the endosperm was rich in starch, and the bran was rich in cellulose and hemicellulose. The starch in the germ was contributed entirely by endosperm im- purity, while the cellulose and heniicellulose came from the bran present in the germ. According t o Fraser and Holmes (1957), the germ hemicellulose was made up of 52.1% xylose, 40.9% arabinose, and 7.0% uronic acid. They also found that the germ contained 3.7% pentosans.

b. Sugars. Using 80% hot alcohol for extraction, Richardson and Crampton (1886) reported 15 to 18% of total sugars in defatted germ. Of this, 80 t o 90% was sucrose. The rest, consisting of nonfermentable, nonreducing sugars (before hydrolysis), was strongly dextrorotatory and was hydrolyzed by yeast invertase t o reducing substances. These characteristics resembled those of raffinose. Frankfurt ( 1 896) reported 24.34% of total soluble carbohydrates. Of these, 6.89% was raffinose, and the remaining 17.4% was presumed t o be sucrose.

TABLE XXXI CARBOHYDRATE COMPOSITION O F COMMERCIAL

M I L L PRODUCTS'

As 9, of total carbohydrate

Nature of carbohydrate Endosperm Germ Bran

Hemicellulose Cellulose Starch Sugars Total

2.4 15.3 43. I 0.3 16.9 35.2

95.8 31.5 14.2 1.5 36.3 7.5

74.1 44.5 60.8

'Calculated from the values reported by 1-raser and Holmes (1959).

WHEAT GERM 23 1

Schulze and Frankfurt (1 894, 1895) reported the presence of both sucrose and raffinose in wheat germ and isolated them in crystalline form. The presence of sucrose and raffinose in commercial wheat germ was confirmed by Power (1913). He isolated and characterized these sugars by their melting points and specific rotations and found that the embryonic axis ’contained a relatively large proportion of glucose, since aqueous extracts of the germ readily yielded glucose phenylosazone. Later, Colin and Belval (1933, 1935) reported a low value of 9.4% for total sugars consisting of 5.2% sucrose, 4.0% raffinose, and 0.2% reducing sugars.

Fraser and Holmes (1 959), Dubois et al. (1 960), Linko et al. (1 960), and Garcia et al. (1 972b) separated and identified the individual sugars of the germ by chromatographic techniques. The component sugars as reported by these workers are given in Table XXXII. The total sugar content was 16.2% in mill germ and 20.1% in dissected germ, as reported by Fraser and Holmes (1959). This suggested that the contamination of mill germ with endosperm and bran portions decreased the total sugar content; the value reported for dissected germ appeared to be more reliable in view of the purity of the germ samples. The total sugar content of about 16% agreed more closely with the value reported earlier by Schulze (1910) than with that of Colin and Belval(l933).

Fraser and Holmes (1959) reported only sucrose and raffinose in dissected germ. On the other hand, they also found, besides sucrose and raffinose, small quantities of glucose and fructose in mill germ. The presence of glucose and fructose was attributed probably to partial hydrolysis of sucrose and raffinose. The percentages of component sugars reported by various workers were comparable (Table XXXII). Linko et al. (1 960) found a sugar, melibiose, which was

TABLE XXXII COMPONENT SUGARS OF WHEAT GERM DETERMINED BY

CHROMATOGRAPHIC TECHNIQUES

Component sugar (as % of total)

Sucrose Raffinose Fructose Glucose Melibiose Unidentified Total sugars

Fraser and Holmes Dubois ef al. Linko er nl. (1959) (1960) (1960)

Garcia et al. (1972b)

62.3 57.6 55.9 37.1 31.6 38.1 - 4.8 2.8 - Trace 2.1

- 1.1 - Trace

16.2’ 16.8‘ 28.6d

- -

64.0 32.0 1.0 2.0a -

2.0

“Include maltose. bOn a 11.7% moisture basis. =On a defatted-germ basis.

a moisture-free basis.


Moisture (%) Moisture (70)

FIG. 10. The effect of moisture content at 35°C and 50°C on the concentration of soluble sugars.

not reported by earlier workers. Also, they suspected the presence of lactose and galactose in the germ samples.

c. Effect of Storage on Sugar Content of the Germ. Linko et al. (1960) determined the sugar content of germ stored for 8 days at different temperature and moisture levels. No change in the sugar content was observed when germ containing 8.9% moisture was stored even at 50°C (Fig. 10). However, changes became more pronounced with increases in moisture content of the germ during storage. Depending on the moisture and temperature of the germ, nonreducing sugars were found to decrease, whereas reducing sugars increased during storage. The decrease in nonreducing sugars was followed by an increase in browning as measured by the fluorescence value. This was due to the reaction of reducing sugars with free amino acids to form an intermediate of nonenzymic browning.

7. Minerals

a. Earlier Work. The work up to 1943 was excellently reviewed by Bailey (1944) in his monograph. The methods followed by earlier workers were mostly colorimetric or titrimetric, and some of the analyses were carried out by methods that are presently regarded as of doubtful accuracy. In some cases, precautions were not taken to avoid the interference of other metals in the estimation. Good agreement was observed in many of the values for different minerals (Table XXXIII). Phosphorus, potassium, and magnesium were the major constituents of germ ash.

In addition to the values for the mineral constituents given in Table XXXIII, the following values (in parts per million) for individual elements have been

WHEAT GERM 233

TABLE XXXl l l MINERAL CONSTITUENTS IN WHEAT GERM

Sullivan Howe and Booth Grewe and McHargue and Near Sullivan Zunini et al. LeClerc

Mineral (1925)' (1927)' (1936)a (1935)a-b (1941)' (1943)'

Phosphorus Potassium Magnesium Calcium Sodium Iron Zinc Copper Manganese Aluminum Sulfur Silicon Chlorine Total ash

-

- 270 160 460 150 -

12,533 5,542 3,081

692

68 420

9 67 25

240

-

-

50,410

10,900

1,600 430 100

- -

2,400 90

10,550 9,300 3,220

550 58

18 208

- 2,350

820 42,600

'As parts per million on a dry basis. bAlso detected Zn, Mn, Fe, N, Al, Cu, CO, and B. 'Mean values (on a 14% moisture basis) for nineteen samples covering five varieties of

wheats.

reported by various workers: copper, 48 (Guerithault, 1927), 12.7 (Lindow et al., 1929), and 9.0 (Elvehjem and Hart, 1929); aluminum, 143 (Bertrand and Levy, 1931); manganese, 225 (Javillier and Imas, 1926) and 190 (Bruere, 1934); zinc, 199 (Javillier and Imas, 1926); lead, tin, and selenium, 1.5, 0.4, and 0.8, respectively (Kent, 1942); and iron, 416 (Andrews and Felt, 1941). The aluminum and manganese contents in the germ were nearly ten to thirty times as high as in other mill products.

b. Phosphonts and Phosphonts Compounds. Phosphorus was the main constituent of germ ash, ranging from 1.04 to 1.41% as reported by several workers. The distribution of phosphorus given in Table XXXIV shows that about 50% of the total phosphorus is phytic phosphorus (Pringle and Moran, 1942; Andrews and Bailey, 1932). Sullivan and Near (1927) reported that the ratio of lipid phosphorus to total phosphorus for patent flour was 0.128, as compared with 0.04 for the germ. Bailey (1944) reported that the inorganic phosphorus content of germ was 0.04%, and it was present mainly as pyrophosphate together with metaphosphate (Sullivan and Near, 1927).

c. Recent Work. Czerniejewski et al. (1964) analyzed various minerals by colorimetric, flame photometric, and titrimetric procedures after separating the


TABLE XXXlV DISTRIBUTION O F PHOSPHORUS IN WHEAT GERM

As % of germ As 7% of total P

J avillier Andrews and Pringle and Andrews and Phosphorus and Colins Zunini Bailey Moran Bailey compound (1933) (1935) (1932) (1942) (1932)

~ 1.244 1.413 - Total 1.355 Extract by 2% HCl ~ - 1.004 - 80.7 Phytin 0.567 0.340 0.597 0.674 48.0 Lipoid 0.120 0.100 0.071 - 5.7 Nuclein 0.379 0.368 Inorganic 0.289 - -

Others - - 0.576 - 46.3

- - -

- ~

TABLE XXXV RECENT DATA O N M I N E R A L CONSTITUENTS OF WHEAT GERM^

Garcia et al. (1972a)b

Waggle et al. Czerniejewski Mineral A B (1967)' et al. (1964)

Phosphorus Potassium Magnesium Calcium Sodium

Iron Zinc Mangdnesc Copper MoIybdenum

1.08 0.95 0.299 0.044 0.01 0

98.0 143.2 148.4

10.3

Percent

1.04 1.01 0.95 1.14 0.319 0.27 0.048 0.05 8 0.027 0.024

Parts per million

102.5 53.6 138.7 134.7 163.7 135.5

9.5 10.2

0.925 0.889 0.268 0.048 0.0232

66.6 100.8 137.4

7.4 0.67

aOn a full fat and dry basis. bMean of triplicate samples. 'Mean value of nine different samples; other minor mineral elements

(as parts per million) are: Ba 8.5, A1 5, Sr 2.36, B 5.7, and Se 0.372.

WHEAT GERM 235

elements interfering in the estimation. Later, Waggle et al. (1967) found that germ samples from nine different wheat mixes contained relatively high amounts of mineral constituents compared with samples from whole wheat and flour. Results were obtained by a computer-programmed emission spectrometer without any mention of sample decomposition or ashing procedures. More recently, Garcia et af. (1972a) used a rapid wet-ashing procedure coupled with atomic absorption spectroscopy techniques. The different mineral values (summarized in Table XXXV) are generally in good agreement except for the iron content. The differences in the values for iron, zinc, and copper were attributed to the differences in the ashing techniques. The data reported by different workers indicate that the germ contained higher concentrations of nutritionally important trace elements like zinc, manganese, copper, cobalt, iron, and selenium.

8. Vitamins

Most of the work on the vitamin contents of the germ has been reported for hand-dissected germ and its structural parts. This has already been discussed (Section IV,A,5). Comparatively, very few data are available on the vitamin contents of mill germ. Bailey (1944) had reviewed the literature on vitamins of milled products. Values reported earlier than 1958 varied widely, as there were no standard methods for estimation. Different biological, chemical, and microbiological methods were adopted by various workers. Only relatively recently, Calhoun et al. (1 958) standardized the procedures and the hydrolysis conditions to be followed for wheat and wheat products for estimating vitamins.

a. B-Group Vitamins. Jackson et al. (1943) determined the vitamin content of mill products and reported values of 21.3 pg of thiamine and 4.53 pg of riboflavin per gram of germ. The germ contained five times as much thiamine as did whole wheat and about twenty-five times as much as did patent flour. Similarly, values for riboflavin in the germ were about four and seven times as high as those in wheat kernel and patent flour, respectively. They found only 42 pg of niacin per gram of purified germ, as compared with 68 pg per gram of mill germ. The higher value in mill germ was due to contamination of the germ with niacin-rich bran portions. Andrews (1 942) and Barton-Wright (1 944) reported comparable values for pure and commercial samples of germ.

Teply et QI. (1 942) reported the following values (in micrograms per gram) for germ: niacin, 34; pantothenic acid, 15.3; and pyridoxine, 9.6. Among the mill fractions analyzed, the germ contained the highest amounts of pantothenic acid and pyridoxine. Moran and Drummond (1945) reported a comparatively low value of 8.5 pg of pantothenic acid per gram of germ. The pyridoxine contents in the germ, as reported by Siegal et al. (1943) and by Moran and Drummond (1945), were 10.6 and 14.0 pglgm, respectively, as compared with 4.2 pg/gm for whole wheat.


TABLE XXXVI

VITAMIN CONTENT OF COMMERCIALLY MILLED WHEAT PRODUCTS~

Vitamins

Thiamine‘ Riboflavin Niacin Pantothenic acidd Folic acid Biotin p-Aminobenzoic acid

Cholinee Inositol Pyridoxine Betaine

Calhoun et al. (1960) Waggle et al. (1967)b

- Whole wheat Patent flours Germ

Micrograms per gram

3.93 0.76 13.5 1.07 0.32 4.87

54.5 10.1 45.3 10.9 4.83 10.4 0.50 0.11 2.05 0.1 14 0.014 0.174 3.83 0.33 3.7

Milligrams per gram

1.63 1.61 2.65 3.15 0.33 8.52

Germ

21.84 5.83 7.5 21.8 2.06 -

-

-

0.01 16 4.83

‘On a 14% moisture basis. bAverage for nine samples. ‘As thiamine hydrochloride. dAs calcium pantothenate. eAs choline chloride.

In later studies, Calhoun et al. (1960) and Waggle et al. (1967) analyzed mill fractions for their vitamin contents by standard methods. The values reported by them (Table XXXVI) compared well and showed that thiamine, riboflavin, folic acid, pyridoxine, betaine, and choline were the highest in the germ.

b. Tocopherols. Wheat germ contained more tocopherol (vitamin E) than any other cereal germ (Green et al., 1955). Mill germ contained 256 to 500 ppm of tocopherols with an average of 332 ppm (Eggitt and Norris, 1955; Eggitt and Ward, 1955; Engel, 1942, 1949; LeCoq, 1944b; Moran et QL., 1954). Eggitt and Norris (1955) reported 3.0 and 2.0 mg of tocopherols in 100 gm of oil extracted from commercial and purified germ, respectively. They separated the individual tocopherols by chromatography and reported 49 to 59% a-tocopherol, 28 to 29% 0-tocopherol, and 1.5 to 9% €-tocopherol. Pure mill germ contained less E-tocopherol compared with commercial germ because of the contamination with a bran portion rich in E-tocopherol. The biological activity of each frac-

tion in terms of a-tocopherol was: a-tocopherol, 100; 0-tocopherol, 30; and E-tocopherol, 7.5 (Ward, 1958). Waggle et al. (1967) reported 3 I to 202 ppm of a-tocopherol in nine samples of the germ.

WHEAT GERM 237

9. Pigments

Apart from traces of carotenes, von Euler and Malmberg (1936) found xantho- phylls as the main pigments of the germ. Flavone-type pigments were reported to be present in mill germ in greater proportions than in the other mill fractions (Simpson, 1935). About 0.2 to 0.3% of glycoflavones were isolated by King (1962) from wheat germ.

10. Other Organic Compounds

King (1 962) detected phenolic compounds such as phenolic, ferulic, and vanillic acids in commercial germ. Daniels and Martin (1967) reported antioxidant properties of wheat germ oil and attributed it to the presence of caffeine and ferulic acid compounds, analogous to the series present in oat kernels. Daniels (1959) detected the presence of methoxyhydroquinone glycosides in the germ and found it to be mostly concentrated in the germ. Andrews and Viser (1951) found 0.1% of oxalic acid in the germ. Swatditat (1974) has reported a thioctic acid content of 36.59 to 41.04 pmoles per gram in wheat germ as compared to 1.37-2.85 pmoles per gram of flour.

11. Enzymes

Being embryonic in nature, wheat germ contains innumerable types of enzymes, as mentioned earlier (Section IV,A,6). Only a few have been reported for dissected germ. Most of the enzyme studies were carried out on mill germ. Some of the important enzymes in the germ were estimated quantitatively, some were crystallized, and others were only detected. Even some of the values for enzymes that were quantitatively analyzed could not be compared with other literature values, as the methods followed and the units of activity expressed were quite different.

a. Lipases. Among the different enzymes present in the germ, lipase is probably the most important enzyme studied. This may be attributed to the major role played by lipase in the development of hydrolytic rancidity during storage of the germ or .products containing germ. Inactivation of lipase assumes paramount importance for improving the shelf life of the germ and germ products. This aspect will be discussed separately in Section VI. Several workers have estimated lipase activity using different substrates, with the exception of Sullivan and Howe (1933). All the workers have reported maximum lipase activity in the germ as compared with other fractions.

Lipase activity in the gem. Pett (1935) reported maximum lipase activity in dissected parts of the germ, concentrated in the scutellum. Using monometric techniques and mono-n-butyrin as a substrate, Miller and Kummerow (1948)

238 S. R. SHURPALEKAK AND P. HARIDAS RAO

reported lipase activity of 132.4 pl of COz for defatted germ, compared with 1.4 PI for patent flour and 3.9 pI for low-grade flour. It is interesting to note that the lipase activity of defatted germ was nearly one hundred times that of patent flour. This lipase activity of the germ agrees with that reported by Engel (1947).

Koch et al. (1954) reported five times as much activity in the germ as in patent flour, using butter fat emulsion as a substrate. Luchsinger et al. (1955) deveI- oped a sensitive method based on the estimation of glycerol released from a monoolein emulsion at pH 7.4 and 30°C for measuring the low levels of lipase activity. No agreement was found between the relative activities estimated by the methods of Luchsinger et al. (1955) and Koch et al. (1954). This was probably due to the differences in pH, substrate, and buffer concentration used in the two methods. However, the lipase activity in the germ was many times that of the endosperm or patent flour, as observed by Engel (1947) and Miller and Kummerow ( 1 948).

With monoolein as substrate, Ferrigan and Geddes (1958) measured the lipase activity of twenty-seven flour streams and five mill feeds from hard red spring wheat and found that the distribution of ash and lipase was similar in the mill streams. Feed streams representing 26.5% of the wheat contained 78.7% of total ash and lipasc. The two germ fractions-fine and coarse-had the highest lipolytic activities of over 2000 units (micrograms of glycerol liberated from monoolein per gram of sample) as compared with 434 units for whole wheat and 12 to 333 units in different flour streams.

Properties of lipase. The properties of wheat germ lipase were exhaustively studied by Singer and Hofstee (1948a, b), Mounter and Mounter (1962), Fink and Hay (1969), Stauffer and Glass (1966), Brouillard and Ouellet (1965), and Dirks et al. (1955). Wheat germ lipase had an optimum temperature of 36 to 40°C (Luchsinger et al., 1955) and an optimum pH of 7.2 to 7.9 for esters of low- as well as high-molecular-weight acids like butter fat and monobutyrin (Singer and Hofstee, 1948a; Koch et af., 1954).

The lipase of wheat germ was concentrated to eleven times the activity of the original extract by Singer and I-lofstee (1948a). They found that only a single enzymc was responsible for the lipolytic activity, which was inhibited by fluoride, p-amino-phenylarsine, and o-iodosobenzoate. Mounter and Mounter ( I 962) suggested that wheat germ lipase functioned more like an esterase than a lipasc.

Lipase fractions. Singer and Hofstce (1948b) found no evidence to prove the presence of more than one enzyme. Stauffer and Glass (1966) separated three enzyme fractions from defatted wheat germ: esterase, with an optimum pH of 7.2 to 7.3; tributyrinase, with an optimum pH of 6.6 to 6.8; and lipase, with an optimum pH of 8.0. Brouillard and Ouellet ( 1 965) chromatographed commercial wheat germ lipase on DEAE cellulose and obtained four fractions which exhib- ited both esterase and acid phosphatase activity. Fink and Hay (1969) studied

WHEAT GERM 239

germ lipase by means of disc electrophoresis and chromatography on Sephadex columns and obtained three different esterase fractions, which differed in their substrate specificity and pH optima,

b. Amylases. Oparin and Kaden (1945) reported that the amylases were not concentrated in the germ. Later, Scholander and Myrback (195 1) investigated the amylase activity of 159 units (milligrams of maltose per minute per gram) in the germ, 192 in bran, and 280 in the flour portion, indicating thereby a relatively low concentration of amylase in the germ. They also reported 5.7 units (relative effect on viscosity) of a-amylase in the germ, which was less than that found in other mill fractions. Proskuryakov and Rodionova (1960) determined the amylase activity in the water-soluble protein fraction of commercial germ.

c. Proteuses. As reported by Pett (1935), protease and dipeptidase activities were concentrated more in the dissected germ. Using edestin as a substrate, Engel and Heins (1947) found 0.8 to 1.3 units of proteolytic activity in the germ, compared with 0.1 unit for the endosperm.

Balls and Hale (1936) expressed proteolytic activity as increased titer value against 0.1 N KOH after enzyme hydrolysis on a portion equivalent to 2 gm of flour. They reported a highest activity of 2.5 ml as compared with 0.45 ml for white flour and 1.6 ml for whole wheat. In contrast, Howe and Click (1946), with casein as substrate, found the proteolytic activity of the germ to be less than that of whole wheat, bran, and shorts. This was probably due to the fact that Balls and Hale (1936) may have used fractions milled from different wheats.

d. Phosphutases. The presence of phytase was reported by Proskuryakov and Rodionova (1960) in commercial wheat germ and by Peers (1953) in dissected germ. Verjee (1969) and Brouillard and Ouellet (1965) separated acid phosphatase from wheat germ by ion-exchange chromatography. The latter workers showed that the wheat germ phosphatase existed in four different active and easily separable molecular forms, which hydrolyzed the esterase substrates. They confirmed the presence of iron in the enzyme.

e. Oxiduses. Lipoxiduse. The presence of lipoxidase in commercial germ was first shown by Sumner (1943), who reported 810 units of activity, defined as activity in the presence of 5 mg of linoleic acid catalyzing the reaction of 1 pg of O2 per minute at 25°C and pH 7.0 by using the thiocyanate method. This activity was 2.5% of the activity in soybean meal.

Later, using the 0-carotene oxidation method, Miller and Kummerow (1948) reported maximum lipoxidase activity in the germ as compared with other mill fractions. The values for destruction of carotene in the germ and commercial flour were 32% and 1.6%, respectively. By the same method, for seven varieties of wheat, Blain and Todd (1955) also reported 58.5 units of lipoxidase activity for the germ as compared with 1.8 units for the endosperm.

Chtuluse. Hawthorn and Todd (1955) reported the possibility of catalase playing a part in the unsaturated fat oxidase system. They observed higher

24 0 S. R. SHURPALEKAR AND P. HARIDAS RAO

activity in purified mill germ as compared with flour and commercial germ, which contained impurities like bran and endosperm having low activity. The relative catalase activity of commercial germ was 83, compared with 1 for the endosperm and 4.4 for bran.

Peroxidase. Hagihara et ~ l . (1958) isolated, purified, and crystallized enzymes peroxidase 556 and peroxidase 566 from commercial germ and found that the yield of peroxidase 566 was very low. By using mild conditions, Tagawa and Shin (1959) and Tagawa et ul. (1959) obtained crystalline peroxidase in larger amounts. Later, Shm and Nakamura (1961) improved the method for the extraction and purification of peroxidases which had distinctly different properties. Further work on the isolation and purification step was reported by Sequi et al. (1 968).

Other Enzymes. Haghara et al. (1958) crystallized cytochrome c from wheat germ. a-Carboxylase from wheat germ was purified 2700-fold by Singer and Pensky (1952). Heinstein and Stumpf (1969) studied the properties of acetyl coenzyme A and purified it more than 1000-fold. Various glycolytic enzymes of wheat germ and their fractionation were reported by Proskuryakov and Loseva (1962). They reported the presence of aldolase, phosphoglycomu- tase, apyrase, and hexose-phosphate isomerase. In addition, the following enzymes were reported to be present in mill germ; they are classified according to the recommendation of the International Union of Biochemistry.

Oxidoreductases Dehydrases (Kretovitch, 1945) Dehydrogenase dihydroorotic NAD (Kapoor and Waygood, 1965) TPNH oxidase (Conn e f al., 1952) 6-Phosphogluconate isocitric dehydrogenase and glucose 6phosphate dehydrogenase (Bar-

Alcohol dehydrogenase (Stafford and Vennesland, 1953) Isocitric dehydrogenase, glutamic dehydrogenase, malic dehydrogenase, and succinic de-

TPNH diphorase (Clum and Nason, 1958) Cystine reductase (Proskuryakov and Rodionova, 1960) Peroxidase isoenzymes (Lanzani et a/., 1967)

Glutamic-pyruvic transaminase, glutamic-oxalacetic transaminase (Priest, 1959) Hexokinase (Inoue and Ito, 1959) Glutamic acid decarboxylase (Cheng et al., 1960) Acetyl coenzyme A, transcarboxylase, acyl coenzyme A, and malonyl coenzyme A

Methyl transferase Sadenosyl methionine-methionine (Karr ef al., 1967) Orotidine-5-phosphate pyrophosphorylase (Kapoor and Waygood, 1965) D-Xylulokinase (Zahnley and Axelord, 1965) Uridine diphosphate-D-glucuronic acid decarboxylase (Ankel and Feingold, 1965 ; Cas-

nett et al., 1953)

hydrogenase (Sisakyan and Vasil’eva, 1954)

Transferases

(Hatch and Stumpf, 1961)

taner and Hassid, 1965)

WHEAT GERM 24 1

Hydrolases Acetylesterase (Jansen et al., 1948) Ribonuclease (Proskuryakov and Nuzhdina, 1960; Lanzani and Lanzani, 1967) Ascorbic acid oxidase, glycerophosphatase, deoxyribonuclease (Proskuryakov and Nu-

Gentobioside (Yamaha and Cardini, 1960) Aldolase, apyrase, and phosphoglucomutase (Proskuryakov and Loseva, 1962) Phosphoglycerol phosphatase (Rao and Vaidyanathan, 1966) Acidic peptidase (Prentice el aL, 1967)

Oxalacetic carboxylase (Kraemer et al., 195 1 ) Synthetase, glucosides, and synthetase gentobioside (Yamaha and Cardini, 1960) Synthetase, adenyl succinate (Hatch, 1966) Synthetase oxalyl coenzyme A (Giovanelli, 1966) Uroporphyrinogen 111 cosynthatase (Stevens and Frydman, 1968)

zhdina, 1960)

Ligases (Sy n thetases)

C. SUMMARY

The exhaustive studies reported on the chemical composition of the germ cover mainly commercial mill germ which is admixed with impurities like bran and endosperm. Separation of dissected germ of high purity is feasible only on a laboratory scale. Information on its composition is scanty and can be considered to be only of academic interest. Dissected germ naturally contains comparatively larger amounts of proteins, sugars, lipids, thiamine, and tocopherols, and lesser amounts of carbohydrates and phytic phosphorus, compared with mill germ.

Compared with wheat flour, the germ is unique in that it provides three times as much protein, seven times as much fat, and about fifteen times as much sugar. In addition, the high sugar content makes it one of the most acceptable foods in its natural form. It is interesting to note that, unlike flour protein, wheat germ lacks in gluten and is rich in salt-soluble proteins. In spite of the high nonprotein nitrogen content of about IS%, the conversion factor used by most of the workers for determining protein remains 6.25. Among vegetable proteins, mill germ has probably the best essential amino acid make-up, which compares well with that of egg protein. It is a rich source of lysine, unlike other cereal proteins. Mill germ has also proved to be an excellent source of B-group vitamins and tocopherols, which enhances the value of the germ as a food supplement. The similarity between the physical properties of germ oil and edible vegetable oils makes it suitable for food uses. Fatty acids of germ lipids are predominantly unsaturated, and over 70% of these are essential ones. However, the high lipase and lipoxidase activities coupled with unsaturated fat pose problems regarding an adequate shelf life of the germ.

The abundant data available on commercial mill germ have clearly shown its great potential as an ideal food by itself or as an effective supplement packed with all the desired nutrients.

24 2 S. R . SHURPALEKAR AND P. HARIDAS RAO

V. NUTRITIVE VALUE OF THE GERM

In human nutrition, cereals, including wheat, have been reported to be poor sources of quality protein. Wheat germ, however, is unique in containing high proportions of protein, edible oil, sugars, certain B-group vitamins, and tocopherols. The biological value of wheat germ proteins has been reported to equal that of highly rated animal proteins. For the nutritional evaluation of different foods, several workers have reported different methods (McLaughlan and Camp- bell, 1969), including chemical methods, rat and chick growth methods, and supplementary value studies. They have also studied the toxic or inhibitory factors present and the effect of processing on the nutritive value of wheat germ.

A. NUTRITIONAL EVALUATlON BY CHEMICAL METHODS

The amino acid composition of the germ has already been discussed (Section IV,A,2). It has been reported that the amino acid pattern of germ protein compares favorably with that of whole egg protein, indicating that wheat germ proteins have a well-balanced amino acid make-up (Barton-Wright and Moran, 1946). The lysine content of germ ranged between 5.5 and 6.5% and was twice that in whole wheat, three times that in white flour, and comparable to that of egg proteins (7.2%). Germ protein was found to be even superior to other first-class proteins with respect to some amino acids like arginine, cystine, and methionine (Barton-Wright and Moran, 1946). The only limiting amino acid of

TABLE XXXVIi

CHEMICAL SCORE 01’ ESSENTIAL AMINO ACIDS OF WHEAT

M I L L P R O D U C T S ~ ~ ~

Amino acid Germ Patent flour Whole wheat

Isoleucine Leucine Lysine Methionine Phcnylalanine Threonine Tryptophan Valine

59c

5 3d

6 9 71

66 69 86 77

68 63 77 74 28d 35d 56 53‘

5 2‘ 55 89 83

74 86 67 71

‘Miladi el QI. (1972). bValues represent amount of amino acid as a percentage of the

amount in egg protein. ‘Second most limiting. dMost limiting.

WHEAT GERM 24 3

the germ was reported to be isoleucine (Mitchell and Block, 1946), the percentage deficit being 62% compared with the isoleucine content of egg protein.

The chemical score, defined as the amount of amino acids present as a percentage of the amount in egg protein, was reported for mill products (Table XXXVII) by Miladi et aI. (1972). A majority of the amino acids had a higher chemical score in the germ than in other milled products. Their observation that methionine was the most deficient amino acid in the germ contradicted earlier findings (Osborne, 1907; Moran et al., 1970) that isoleucine was the most deficient amino acid, and methionine the second limiting one. The difference was attributed to the variation in the composition of the sample tested or to differences in the amino acid requirements of experimental animals and their species.

Block and Mitchell (1946) reported an inverse relationship between the chemical score (defined as 100 - % deficit in the most limiting amino acid compared with egg protein) and the biological value as shown by rat growth experiments. Interestingly enough, wheat germ was rated much lower according to its chemical rating compared with its actual biological performance. This was attributed to the higher proportion of nonprotein nitrogen present in the germ, which probably contributed to the biological value.

Using different parameters, Kasarda et al. (1970) evaluated the amino acids of mill products by determining (1) the ratio of the essential to the total amino

TABLE XXXVIII NUTRITIVE VALUE OF MILL PRODUCTS OF WHEAT AND WHOLE EGG PROTEIN"

Essential amino acid Egg reference protein Whole wheat Flour Wheat germ

E/T valuesb 3.22 1.99 2.01 2.26 A / E valuesC

Total aromatic amino acids 195 24 3 239 192 Total sulfur amino acids 107 196 115 109 Threonine 99 93d(94)e 83d(84)e 104 Tryptophan 31 41 37 36 Valine 141 150 138 145 Isoleucine 129 122d(95)e 120d(93)e 99d(77)e Leucine 172 213 210 170 Lysine 125 82d(66)e 59d(47)e 145

'Kasarda et al. (1970). bEssential amino acids (gm) + total amino acids (gm). cSpecific amino acid (mg) + total essential amino acids (gm). dValues that are at least 5% lower than the reference pattern. eValues A / E for specific amino acid i A / E for reference pattern X 100. The lowest value

shows the first limiting amino acid.


acids (E/Z"); (2) the patterns of essential amino acids compared with those of a reference whole egg protein; and (3) the ratio of specific essential amino acid to the sum of the essential amino acids (A/E). The nutritive values of proteins of different mill products including the reference whole egg protein are given in Table XXXVIII.

Even though the EIT value for egg protein was much higher than that for germ protein, such a high E/T ratio was not necessary for the most efficient use of its amino acids. Only 50% of the essential amino acids of egg protein have been reported to be utilized by human adults for maintaining nitrogen balance (FAO/WHO Joint Expert Group, 1965). It was further confirmed from the A / E values that wheat germ showed much better balance and isoleucine was found to be the only limiting amino acid.

B. NUTRITIONAL EVALUATION BY BIOLOGICAL METHODS

1. Rat Growth Experiments

Studies carried out by Boas-Fixsen and Jackson (1932) and by Chick et al. (1935) clearly indicated that the biological value of wheat germ was dependent on the level of protein in the diet. They reported biological values of 69 and 90 at 6.8% and 3.6% levels of protein, respectively, in the diet.

Hove and Harrel (1943) found that the quality of wheat germ protein was at least as good as that of animal proteins when the diet contained 5% protein. They further determined the protein efficiency ratio (PER) of wheat germ at a 10% level of protein and observed that a slight variation in the level of the dietary protein affected the PER. The PER decreased from 2.87 to 2.41 when the protein content in the diet was increased from 9.3% to 11.7%. The PER of animal proteins included for comparison and fed at the 10% level were: casein, 2.3; dry skim milk, 2.85; and boiled dry egg white, 2.58.

A similar inverse relationship between dietary protein and the PER was also observed by Sure (1957). According to him, 15% protein was the most efficient level of protein intake. A higher protein intake resulted in wastage during metabolism.

Jones and Widness (1946) compared the nutritive value of wheat germ with that of corn germ, soybean, peanut and cottonseed flours, dried whole egg powder, dried skim milk powder, and casein. The different diets were adjusted so that they were isocaloric and nutritionally adequate with respect to dietary factors other than the protein. The PER of wheat germ was much higher than that of the oilseed flours and was equal to that of the skim milk powder. Also, wheat germ was found to be nutritionally (PER) better than corn germ at any protein level.

WHEAT GERM 245

8 0 .

TABLE XXXIX PROTEIN QUALITY OF M I L L PRODUCTS OF WHEAT'

Protein level Mean weight Mean protein Mean protein in diet gain consumed efficiency

Product (%) (sm) (gm) ratiob ~ ~

Whole wheat 10.2 41.9 30.0 1.40 Wheat germ 10.1 131.8 45.9 2.81 Wheat bran 9.9 101.5 47.3 2.15 Patent flour 9.8 19.2 22.9 0.84 Nonfat dry milk solids' 9.6 125.0 44.1 2.84

'Hove et al. (1945). 'Ten rats per group fed for a period of 6 weeks. 'Values from a separate experiment given for comparison.

The nutritional superiority of wheat germ over other mill products was reported by Osborne and Mendel (1919), Hove et al. (1945), and recently by Miladi et al. (1972). Wheat germ had a higher PER (Table XXXIX) than any of the other mill fractions (Hove el al., 1945), and the PER compared well with that of nonfat dry milk solids as reported earlier by Hove and Harrel (1943). Recently, the relative nutritive value (RNV) (defined as the slope of the dose- response curve obtained with the protein under test, divided by the slope of the response curve obtained with standard protein lactalbumin) and in vitro digestibility of wheat proteins from different mill fractions were determined by Miladi et al. (1972). The gain in body weight and body water after a 3-week experimental period have been used as a measure of the response. The RNV of the patent flour was the lowest (25%), and wheat germ had the highest RNV of 80% (Fig. l l ) , which was even higher than the 74% for casein reported by Hegsted and Chang (1965).

shorts, .:germ flour ,.,

1' 01 1' I I I I I

1 2 3 4 5

Total lysine (grnA6 grn N)

FIG. 11. The relative nutritive value (RNV) of different mill products.


TABLE XL

EVALUATION OF PROTEIN QUALITY OF WHEAT GERM'

Protein source Wciglit gain Growth

(smIb index

Isolatcd soy protein (ncgative standard) 290 100 Viobin fish flour (positive standard) 393 135 Soy f lour 368 127 Solvent defatted wheat germ 396 136 Isolated wheat germ protein 369 127

Least significant range (P = 5%) 16

'Rand and Collins (1958). bEqualized pain over protcin-frec diet.

2. Chick Feeding Trials

Using growing chicks, Rand and Collins (1958) evaluated the nutritional quality of wheat germ along with that of other animal and oilseed proteins. The results, presented in Table XL, indicated that the nutritive value of defatted wheat germ equaled that of Viobin fish flour used as positive control. Hinners (1958) has reported that high-quality fish meal was even superior to egg white as a sole source of protein. It may thereby be inferred that the wheat germ protein was also superior to the egg white proteins. These results of chick feeding trials have confirmed the earlier finding with rat growth trials. I t is, however, interesting to note that the protein isolated from wheat germ had a lower protein quality index than the parent material. On the basis of net protein utilization (NPU) values, Moran et al. (1970) reported that wheat germ compared favorably with soy flour.

Cave et al. (1965), while evaluating the proteins of a series of wheat by-products, found that the growth of chicks was relatively rapid when they were fed on wheat shorts or wheat germ meal diluted with 50% of a corn-soybean ration. Using the growing chicks, Summers et al. (1968) reported a PER of 3.06 and an NPU of 58.8 for nine samples of germ. They further evaluated the various wheat fractions obtained from wheat samples for metabolizable energy (ME), metabolizable dry matter (MDM), and NPU. Wheat germ had a higher ME (2.50 kcal/gm) and a higher MDM (57.5%) than other mill fractions such as shorts and bran.

C. SUPPLEMENTARY VALUE OF WHEAT GERM

Generally, protein-rich foods are used as supplements to improve the nutritive value of different staple diets based on cereals and millets. The supplementary

WHEAT GERM 24 7

value of wheat germ to wheat flour, gluten, barley, corn, rice, etc., has been studied by several workers.

1. Germ as a Food Supplement

Hove and Harrel (1943) reported that the biological value of poor-quality vegetable protein could be improved to the same extent by supplementing either with wheat germ or with casein. The PER of gluten increased from 0.43 to 2.12 and 2.38, when 25% of the gluten was replaced by wheat germ and casein, respectively. Because of good-quality protein and high levels of thiamine, niacin, and many essential minor elements such as copper, iron, and zinc, these workers found that the addition of wheat germ to the American dietary would not only improve the nutritional quality of the diet but could also replace some of the animal proteins in the diet.

Supplementation of patent flour with various levels of low-fat wheat germ markedly improved the PER (Hove er al., 1945). Supplementation with even 3% germ improved the PER of patent flour from 0.84 to 1.19. Beeson er al. (1947) found that supplementing the peas with 25% or 50% of germ brought about a

TABLE XLI IMPROVEMENT IN THE NUTRITIVE VALUE O F CEREALS WITH DEFATTED WHEAT

GERM FLOUR'

Level o f germ added

I 0% 15%

Ad libitum Equalized gainb Increase gain' Increase

Diet Protein source (pm) (%) (gm) (%I 1 2 3 4 5 6 7 8 9

10 1 1

Wheat flour 1 + D W G F ~ Rice 3 + DWGF Barley 5 + DWGF Oat 7 i DWG?: Cereal mixture 9 + DWGF DWGF

107 157 138 185 159 202 221 248 128 1 5 1 396

120 46 202 69

139 34 236 69

161 27 252 56

28 1 13 369 31

- - 18 463

'Rand and Collins (1958). bFeeding period: 7 days. 'Calculated for the same feed intake. dDWGF-defatted wheat germ flour.


significant improvement in the growth-promoting value. Westerman e f al. (1952) reported that the addition of defatted germ to enriched flour at 4% and 6% levels increased the growth rate of rats, but 2% of germ had no effect. However, addition of even 2% of defatted germ to flour that had not been vitamin-enriched resulted in increased growth rate, better reproduction and lactation performance, and increased storage of some vitamins, particularly pantothenic acid in the livers of rats.

Crampton and Ashton (1943) observed that supplementing the endosperm of corn, barley, or wheat with wheat germ significantly improved the growth of hogs. Using chicks, Rand and Collins (1958) determined the supplementary value of the germ to wheat flour, rice, barley, oats, and mixtures of equal parts of these cereals by adding 10% and 15% of defatted and light-toasted wheat germ. They observed a striking improvement in chick weight at the 10% level of the germ supplement. The maximum improvement was observed for rice, and the least for oats. At the 15% level, the weight gain was more significant in all the cereals (Table XLI).

2. Germ Compared with Other Food Supplements

Hove et af. (1945) observed from their rat growth experiments that the supplementary value of wheat germ to patent flour was the same as that of nonfat dry milk solids and corn germ meal. However, wheat germ was superior to corn germ (Table XLII) as a supplement to wheat flour (Stare and Hegsted, 1944) and peas (Beeson et al., 1947). Similarly, at the 3% level, Westerman et al. (1954) observed that the supplementary effects of soy flour and wheat germ to nonenriched wheat flour were comparable.

TABLE XLII SUPPLEMENTARY VALUE O F WHEAT AND CORN GERM PROTEINS TO

PATENT FLOUR'

Total protein Protein Total protein Prdtein from supplement efficiency from supplement efficiency

Protein supplement (%) ratiob (%I ratiob

None 0 0.78 - - Dry skim milk 20 1.45 50 2.26 Defatted wheat germ 20 1.52 5 0 2.26 Defatted corn germ 20 1.13 50 1.71 Soybean oilmeal 20 1.23 50 1.77

'Stare and Hegsted (1944). bDetermined for 3-week period.

WHEAT GERM 24 9

3. Other Beneficial Effects

In addition to improved growth observed as a result of feeding germ supplements, other beneficial effects have been reported. Crampton and Ashton (1943) found that wheat germ had a tendency to stimulate or facilitate synthesis and deposition of body fat from dietary carbohydrates. LeCoq (1944a) observed that the edema and neuromuscular troubles developed by rats fed low-protein diets containing theobromine or caffeine could be prevented by the addition of 40% wheat germ meal to the protein-poor diets. Morgulus and Spencer (1936) reported that muscular dystrophy of rabbits could be prevented by the addition of wheat germ.

D. EFFECT OF PROCESSING ON THE NUTRITIVE VALUE OF THE GERM

Raw wheat germ was found to have a “feedy” taste and smell and poor stability owing to hydrolytic and oxidative changes in the germ lipids (Sherwood et al., 1933). These defects have been overcome by heat processing of the germ (discussed in Section VI,B). Hove and Harrel (1943) have found that heat processing of wheat germ, to make it suitable for human consumption and to improve its keeping quality, had no effect on the nutritive value of protein as determined by the PER.

The effect of several processing methods on the nutritive value of defatted germ was studied by Rand and Collins (1958) by the chick growth method. The processing of the germ was carried out either by light toasting of the material,

TABLE XLlII EFFECT O F MILD HEATING ON PROTEIN QUALITY O F

DEFATTED WHEAT GERM‘

Weight gain Protein efficiency ratio b

Protein source (sm) DWGC (untreated) 186 4.1 DWC laboratory steamed 209 4.8 DWG steamed in pilot plant 202 4.8 DWG light toasted 214 4.8 Isolated soy protein 142 3.4 Viobin fish flour 204 5.0

‘Rand and Collins (1958). bFor 1-week period. ‘DWG-defatted wheat germ.


until it attained the light-brown color desired, or by steaming the germ at atmospheric pressure for 20 minutes. Light toasting or mild steaming improved the protein quality of wheat germ as shown by the weight gains (Table XLIII). This confirmed the earlier findings that plant proteins improved in digestibility and biological value as a result of heat treatment (Gray et al., 1957). However, severe heat treatment of the germ had an adverse effect on its nutritive value, as shown by the reduction in the weight gain of chicks from 428 to 248 gm, when they were fed pressed, defatted germ. Rand and Collins (1958) suspected this low value to be due to the severe heat development during expeller-pressing of the germ.

The effect of heat treatment on the quality and utilization of germ proteins was studied by Olsen (1967) by feeding weanling rats, The heat treatments consisted in toasting germ in a rotary drum dryer at a product temperature of 121°C for 45 minutes and autoclaving at 15 pounds of pressure (121°C) for 20, 45, and 90 minutes. Soybean meal was included for comparison. The results of the studies, reported in Table XLIV, confirmed the excellent nutritional qualities of wheat germ. However, heat processing of the germ decreased the nutritive value as shown by the lower PER of the processed germ, depending on the severity of processing.

Olsen (1 967) also found that only arginine and lysine contents were affected to a significant extent by the heat treatment. The arginine content decreased by 7% in toasted samples as well as in samples autoclaved for 20 minutes, and by 12% and 27% in the samples autoclaved for 45 and 90 minutes, respectively. The loss of lysine was even greater than that of arginine-12% for toasted' samples, and 16%, 25%, and 42% for samples autoclaved for 20, 45, and 90 minutes,

TABLE XLIV EFFECT 01: HEAT TREATMENT ON THE NUTRITIVE VALUE OF WHEAT GERM

MEAL P R O T E I ~ ~ . ~

Diet

Soy bean meal W G M , ~ raw WGM, toasted WGM, autoclaved, 20 minutes WGM. autoclaved, 45 minutes WGM, autoclaved, 90 minutes

Weight gain (gm)

37.1 + 1.08' 36.1 k 0.82' 28.2 + 1.25' 30.9 + 1.12' 18.0k 0.52'

7 .3? 1.16'

Feed consumed Protein k m ) efficiency ratio

85 86 80 84 69 60

3.40 3.50 2.84 3.12 2.31 1.00

'Olsen (1 967). %slues are means for six rats per group; duration of experiment 7 days. 'Standard error of mean. dWGM-wheat germ meal.

WHEAT GERM 25 1

respectively. The losses of other amino acids were negligible, as seen in Table XLV.

Toasting had the least effect on the percentage of absorption of amino acids and nitrogen; autoclaving decreased the same values by 2 to 4%. However, compared with values for raw germ, the absorption values of amino acid and nitrogen decreased to 77% and 63% in samples autoclaved for 45 and 90 minutes, respectively. Some of the amino acids were affected to a greater extent on autoclaving of the germ for 90 minutes. The decreased values for absorption were 42% for lysine, 54% for isoleucine, 56% for vdine, and 58% for leucine. The destruction in the amino acids and the decrease in absorption were reflected by lower weight gain and protein utilization by rats, as shown in Table XLVI.

TABLE XLV

AMINO ACID COMPOSITION' O F HEATED WHEAT

GERM M E A L S ~ ~ ~

Wheat germ meal

Autoclaved

Amino acid Raw Toastedd 20 45 90

Essential Arginine Histidine Isoleucine Leucine Lysine Methionine Phen ylalanine Threonine Tryptophanf Valine

Nonessential Alanine Aspartic acid Glutamic acid Glycine Proline Serine Tyrosine

1.58 1.01 1.02 6.65 5.54 2.42 2.22 2.28 2.22 2.16 3.46 3.15 3.21 3.22 3.34 6.24 6.01 6.15 6.11 6.05 6.50 5.69 5.45 4.85 3.79 1.27 1.29 1.22 1.22 1.21 3.53 3.28 3.30 3.34 3.31 2.68 3.05 2.12 2.92 2.93 0.98 0.96 0.96 0.96 0.96 5.39 5.05 5.29 5.08 5.10

6.24 5.69 5.11 5.92 5.96 8.43 1.65 1.53 1.75 1.20

14.38 13.10 14.20 14.63 14.49 6.24 5.66 5.80 5.59 5.64 4.05 4.18 4.29 4.15 4.30 2.19 3.09 2.44 2.83 2.87 2.22 2.22 2.18 2.19 2.23

'Grams per 16 gm of nitrogen. bOlsen (1 961). CMicrobiological method on acid hydrolyzate (except for tryptophan). dAt a product temperature of 121°C for 45 minutes. eAt 15 psig. fMicrobiologica1 method on alkaline hydrolyzate.


TABLE XLVI GROWTH, FEED EFFICIENCY, AND NET PROTEIN UTILIZATION BY CHICKS FED

WITH HEAT-PROCESSED WHEAT GERM'

Weight at 3 weeks Weight gain/ Net protein Processing treatment (gm)b feed consumed utilization'

Nitrogen-free diet 47 Wheat germ

Raw I35 Toasted 154 Autoclaved at 15 psig for

20 minutes 127 45 minutes 118 90 minutes 83

Isolated soybean protein 159

0.35 47.7 0.38 53.0

0.33 48.4 0.29 43.9 0.13 32.9 0.42 59.4

'Moran et al. ( 1 968). bAverage I-week starting weight was 67 gm for each treatment. The 3-week weight

'Feeding period 2 weeks. represents an average of four pens of chicks. Each pen had ten chicks.

Unlike Olsen (1967), who reported detrimental effects of heat treatment, Moran et al. (1968), in their experiment with growing chicks fed on heat- processed wheat germ meal, found an improvement in the protein quality after toasting. However, autoclaving for more than 20 minutes at 15 pounds of pressure reduced the weight gains and the NPU values below those observed for raw germ. The NPU values reported at 15% dietary protein level are given in Table XLVI. The observed difference in the quality of toasted or autoclaved germ was reported to be due to moisture content, which could affect both the degree of denaturation and the rate of browning, resulting in the unavailability of certain amino acids. The superiority of toasted germ over germ autoclaved for more than 20 minutes was attributed to the low moisture content of the toasted germ as well as to the removal of moisture during the toasting process. The denaturation occurring during toasting appeared to be sufficient to improve digestibility of proteins but not adequate to destroy the limiting amino acids. The low nutritive value of the autoclaved samples was reported to be due to greater destruction of lysine and arginine in the presence of moisture. Moisture probably facilitated the browning reaction of amino acids with free sugars.

The effect of heat treatment on the metabolizable energy (ME) of wheat germ meal was studied by Bayley er al. (1968). They found that the processing effect on the ME varied for different classes of birds-chicks, roosters, and turkeys (Table XLVII). The ME values of the diet containing raw germ for both chicks and roosters were similar. Toasting the germ had no effect on the ME values for chicks, but caused an increase in roosters. Autoclaving resulted in increased ME

WHEAT GERM 25 3

TABLE XLVIl EFFECT OF HEAT PROCESSING O F G E R M ON THEIR

METABOLIZABLE ENERGY VALUESa

Metabolizable energyb (kcal/gm)

Gross energy Young Turkey Processing treatment (kcal/gm) chicks Roosters tom

Nil (raw) 4.48 2.85 2.91 3.26 2.85 3.19 3.28 Toasted -

Autoclaved at 15 psig for: 20 minutes - 2.69 3.53 3.20

2.77 3.19 3.08 45 minutes -

90 minutes - 2.75 3.31 2.68

‘Bayley et al. ( 1 968). bOn a 90% dry-matter basis.

-

values for roosters, while values for chicks decreased. The ME values of the raw and toasted wheat germ meals for turkey were found to be similar t o those of the toasted wheat germ meals for roosters. However, autoclaving the germ for a longer time reduced its utilization by turkeys by about 18%.

E. EFFECT OF SUPPLEMENTING THE GERM WITH AMINO ACIDS

1. RawGem

Olsen (1967) reported that raw wheat germ supplied less of the essential amino acids than the requirement of rats based on the calculation of the available amino acids (the amino acid content of the germ X percentage of absorption) in the germ. He found that it was necessary to supplement the germ with methionine, threonine, phenylalanine, lysine, isoleucine, valine, leucine, and tryptophan to meet the NRC (National Research Council, United States) requirements for the rat. The results of growth experiments with rats fed on raw wheat germ meal supplemented with only methionine at three different levels and also with the above-mentioned amino acids are given in Table XLVIII. The data indicated that improvements in the nutritive value of wheat germ supplemented either with methionine alone or with the amino acid mixture (calculated to be deficient) were comparable. Although the calculated requirement was 0.25% of methionine, maximum growth was noticed in the diet containing only 0.20% of methionine. It may therefore be inferred either that methionine was underesti- mated in the protein hydrolyzates or that cystine met more than one-third of the sulfur-amino acid requirement.


TABLE XLVIll EFFECT O F AMINO ACID SUPPLEMENTATION ON NUTRITIVE VALUL O F WHEAT

G E R M MEAL I'ROTEINS'

Weight pain Feed consumed Protein Diet (gm) (gm) efficiency ratiob

Soybcan mcal + 0.20% mcthionine 68.0 f 1.95 178 r 2.93

WGM + plutamic acid + ammonium citratc 58.4 f 2.50 178 f 4.43 WGM + 0.1 5'X Ill-methionine 66.0 + 2.70 1 7 1 ? 4.29 WGM + 0.20%. DL-methionine 72.1 f 1.83 176f 4.34 WGM + 0.25'2 DL-methionine 65.1 + 2.26 167 f 3.47 WGM + amino acid mixture I" 167 f 3.26 WGM + amino acid mixture I l d 167 r 2.56

Wheat gcrni meal (WGM) 59.8 r 2.81 175 f 5.59

67.0 f 2.1 3 68.1 r 0.97

2.8 1 2.53 2.43 2.77 2.97 2.8 1 2.99 2.87

'Olscn ( I 967). bIktermined for a 2-week period. 'Contained (as percent of the diet) DL-methionine, 0.20; L-threonine, 0.19; L-phenyl-

alanine, 0.18; L-lysine, 0.1 2; L-isoleueine, 0.10; L-valine, 0.06; L-lcucine, 0.04; and L-tryptophan, 0.03.

dSamc as aniino acid mixture I except for only 0.09% L-phenylalanine.

Miladi et al. (1972) did not find any improvement in the relative nutritive value (RNV) of the germ when it was supplemented with lysine.

2. Processed Germ

In order to overcome the deleterious effect of processing on the nutritive value, Moran et al. (1968) carried out an experiment by feeding chicks with diets containing differently processed wheat germs, which were also supplemented with deficient amino acids-namely, methionine, glycine, cystine, phenylalanine, and tryptophan. Moran et al. (1968) found that supplementing differently processed germ with glycine had no effect on the growth of chicks or on the utilization of feed. However, supplementation with methionine significantly improved the growth of chicks fed with all diets containing processed germ except the diet based on germ autoclaved for 90 minutes. In addition to glycine and methionine, supplementation with tryptophan and phenylalanine did not improve the nutritive value any further. By supplementing the processed germ with an amino acid mixture containing methionine, cystine, lysine, and arginine, Moran et al. (1968) reported an improvement in the feed efficiency and the growth of chicks. However, by eliminating each amino acid from the amino acid mixture, they observed that deficiencies in lysine and arginine were not encountered until the meal was autoclaved for 90 minutes.

WHEAT GERM 255

F. TOXIC FACTORS IN THE GERM

Bakke et al. (1930) observed a color change from black to silver gray in the coats of rats receiving a germ diet, whereas a whole wheat diet did not have any effect. However, if the germ diet was continued for long, the coat color returned to normal. They inferred that wheat germ contained a toxic element which was neutralized by feeding the whole grain. They also assumed the development of immunity to the toxicity after long-term feeding with the germ. Famiani (1932) reported that the germ did not make a complete food for rats, as the sexual functions did not develop adequately when only the germ was fed.

Creek (1955) first observed that substitution of 15% and 30% of wheat germ for corn meal significantly depressed the growth of chicks, which could not be accounted for by the difference in the calories, minerals, bulk, or amino acids. He suspected that the poor growth was due to some toxic factors present in the germ.

Later, Creek et al. (1961) replaced 30% and 55.5% of corn flour in the diets with raw and autoclaved (30 minutes at 15 pounds of pressure) germ and fed young chicks these diets for 10 to 13 days. The data on growth and feed conversion of chicks given in Table XLIX confirmed the earlier finding that raw wheat germ depressed growth and feed efficiency, depending on the amount incorporated in the diet. Improvement in both growth and feed conversion in rats fed an autoclaved germ diet indicated the presence of a thermolabile toxic factor which impaired digestion. The behavior of the raw wheat germ was

TABLE XLIX

EFFECT O F RAW AND AUTOCLAVED WHEAT GERM MEAL ON GROWTH AND

FEED CONVERSION BY CHICKS'

Trial Group Diet Weight gain Feed/

weight gain

I 1 Control (C) 162 1.54 2 c + 30% WGM' 136 1.59

I1 1 Control (C) 89 1.64 2 C + 55.5% WGM 69 2.00

3 C + 30% autoclaved WGMd 150 1.58

3 C + 55.5% autoclaved WGMd 91 1.58

aCreek etal. (1961). bAverage values for 10 days of feeding. Significantly different at 1% level: 1 versus 2 and

2 versus 3 in trial I; and 2 versus 1 or 3 in trial 11. Significantly different at 5% level: 1 versus 3 in trial I.

'WGM-wheat germ meal. dAt 15 psig for 30 minutes.


reported to be similar to that of raw soybean containing trypsin inhibitor (Brambila et aL, 1961). Determination of the weight of the liver and pancreas of chicks fed the diet containing 55.5% germ showed significant hypertrophy of the liver in birds receiving raw germ. Brambila el al. (1961) suspected that enlarge- ment of the livers was probably due to some compensatory mechanism, similar to that existing in thyroid function.

Creek and Vasaitis (1962) further isolated from raw wheat germ a water-soluble factor which inhibited the enzymic digestion of protein. It was thermolabile and very much like the antitrypsin factor found in raw soybean. By analyzing the feces of chicks fed diets containing raw and autoclaved wheat germ, as a sole source of protein, they found that utilization of protein in chicks fed the diets containing raw or autocfaved germ was nearly the same. On the contrary, rats receiving the raw germ excreted about six times as much fat as those receiving the autoclaved germ (Table L). Creek and Vasaitis (1962) inferred that some toxic factors present were blocking the utilization of fat. Using ether-extracted germ, these workers later confirmed that some factor was acting on the fat added to the diet and not on the germ fat. However, they found that nitrogen retention was also improved by the autoclaving treatment, although not to the same extent as fat utilization.

Depressed growth as well as fat utilization of raw germ observed by Creek et al. (1962) was further confirmed by Parrish and Bolt (1963). On close observation, however, they found that the diet containing raw wheat germ formed a paste on the beaks in combination with salivary mucus and water. Consequently, these birds consumed correspondingly less of the diet and hence did not grow well. They also observed that the birds receiving the raw germ diet were cleaning their beaks on the wire floors, thus adding sufficient feed fat directly to the excreta. Use of autoclaved germ in the diet altered its consistency so that it did not form a sticky paste and the birds could eat it without any difficulty. Therefore these workers did not believe in the presence of a toxic factor.

TABLE L EFFECT OF FEEDING CHICKS WITH RAW OR AUTOCLAVED

WHEAT GERM MEAL AS SOLE SOURCE OF PROTEIN^

Raw WGMb Autoclaved WGMC

Weight gain (gm/20 days) 141 21 2.0 Percent nitrogen excreted 41.8 36.6 Percent fat excreted 40.8 6.8

OCreek and Vasaitis (1962). bWGM-wheat germ meal. CAt 15 psig for 30 minutes.

WHEAT GERM 257

Like Parrish and Bolt (1963), Attia and Creek (1965) also observed the formation of paste on the beaks for some of the raw germ samples, but they felt that it was not the sole reason for the poor growth of the chicks. Consequently, to prevent the formation of paste with saliva, they conducted experiments with young chicks by feeding an ultra-high-fat diet. Care was also taken to avoid the possibility of the feed fat’s entering directly into the excreta on the wire floor. The results, given in Table LI, confirm their earlier findings that raw germ depressed growth and interfered with fat absorption. They inferred that the problem of low nutritive value of raw germ was very similar to that of raw soybean which contained hemagglutinin and trypsin inhibitor and reported 2500 units of hemagglutinin in rabbit blood and 5000 units in chick blood per gram of germ. They also observed the pancreatic hypertrophy of the liver. However, autoclaving overcame all detrimental properties of wheat germ.

Cave et al. (1965) fed raw wheat germ meal to young chicks at a level of 50% added to a corn-soybean meal diet and observed no adverse effect on growth or on carcass protein. Rehfeld (1967) and Olsen (1967) found no toxic components in raw wheat germ and reported that high nutritional value was reduced by heat treatment.

The presence of hemagglutinin and antitrypsin activity in raw germ was further proved by Moran et al. (1968), who estimated their activity by following the method of Liener and Hill (1953) modified by Attia and Creek (1965). Toasting almost completely destroyed hemagglutinin and antitrypsin activity. Autoclaving reduced the toxic factors to zero values (Table LII). Trypsin inhibitor from wheat germ with a molecular weight of 17,000 was isolated and purified later by Karl et al. (1969).

TABLE LI EFFECT O F FEEDING RAW AND AUTOCLAVED WHEAT GERM ON GROWTH,

PANCREAS SIZE, FAT ABSORPTION, AND FEED RETENTION I N CHICKS‘

Body weight Pancreas size Consumed (gm) (mg/lOO sm) fat (%) after: after: excreted in:

Trial Diet 2 weeks 3 weeks 2 weeks 3 weeks 2 weeks 3 weeks

- - I Raw germ 215 - 462 33.3

I1 Rawgerm 174 Autoclaved germb 236 - 413 13.6 - -

Autoclaved germb 201 - - - - 24.03 - 12.6

111 Rawgerm 146 283 - 343.0 - 26.5 Autoclaved germb 205 364 - 264.0 - 11.6

- - -

‘Parrish and Bolt (1963). bAt 15 psig for 30 minutes.


TABLE LII EFFECT O F PKOCESSING WHEAT GERM ON HEMAGGLUTININ

AND ANTITKY PSIN A C T I V I T Y ~ , ~

Hemagglu tinin activity‘

Heat treatment of germ Regular Papain Antitrypsin activity

Nil (raw) 2560 5120 Very high Toasted Nil 20 Trace Autoclavcd at 15 psig for:

20 minutes Nil 320 Nil 45 minutes Nil 160 Nil 90 minutes Nil 160 Nil

‘Moran et al. (1968). bAll data have been expressed on a 14% moisture basis. ‘Expressed as dilution necessary to attain zero activity.

G. SUMMARY

It can be inferred from different studies carried out by several workers that wheat germ proteins have a very well-balanced amino acid make-up. The amino acid composition is quite similar to that of egg proteins as indicated by its chemical score. When cereals in general are deficient in lysine, wheat germ is a rich source of lysine. The only limiting amino acid reported was isoleucine.

Nutritionally, wheat germ is much superior to other milled products of wheat. Feeding trials with rats, chicks, and other animals have shown conclusively that the nutritive value of the germ is equal to that of any animal protein such as egg, casein, skim milk powder, or fish flour and is much superior to that of protein-rich oilseed flours. Similarly, wheat germ has excellent supplementary value when added to other cereal proteins and compare favorably in this respect with nonfat dry milk solids. Mild heat processing or light toasting of germ improves its nutritive value, probably owing to an improvement in the digestibility of the proteins or to destruction of antinutritional factors like hemagglutinin or trypsin inhibitors, whose presence in the germ is well established. Severe heat processing lowers the nutritive value considerably, depending on the extent of the heat treatment.

VI. STORAGE AND STABILIZATION OF THE GERM

The usefulness of wheat germ as a rich source of vitamins and proteins is so well recognized that it is used in its natural form as a component of several

WHEAT GERM 25 9

speciality foods. Extracts of the germ are also used in certain vitamin concentrates. As wheat germ contains a high amount of fat, predominantly unsaturated, protein, and several hydrolytic and oxidative enzymes, it is natural to expect changes in the fat or protein, resulting in the development of an objectionable odor and taste on storage. The demand for wheat germ as a special food has consequently attracted several workers to study its keeping quality and methods to improve this quality.

A. STORAGE STUDIES

Only a few researchers have systematically studied the shelf life of differently packed wheat germ as influenced by various conditions such as moisture and temperature. The spoilage of the germ during storage has been attributed to different enzymes. Various methods have been suggested to evaluate the freshness or spoilage of stored germ.

1. Effect of Packing under Vacuum or Inert Gases

Sherwood et al. (1933) studied the shelf life of whole wheat germ packed in vacuum or with inert gases like nitrogen or carbon dioxide at various temperatures. Alcoholic acidity was used as a measure of the freshness or the spoilage of the germ during storage. Even when samples were stored under the same condition, the acidity changes of vacuum-packed germ were dependent on the purity of the germ. Considering acidity changes as well as organoleptic quality, vacuum-packed germ was found to be better than that packed under inert atmosphere. Pearce (1943) also observed that packing under nitrogen or pellet- ing of the germ was desirable for a longer shelf life.

2. Effect of Temperature

Sherwood et al. (1933) observed that the increase in germ acidity was a function of temperature. Acidity increased eight times as fast at 29°C as at -10°C. In the majority of cases, no unpleasant flavor was observed until the acidity exceeded 0.25%. The germ packed either under vacuum or under nitrogen kept well for over 338 days at -10°C and only for 90 days at 29°C. From their studies on the effect of storage temperature on acidity changes in vacuum- packed germ (Table LIII), they concluded that the germ could be stored under vacuum for a minimum period of 6 months, with the temperature ranging between -10°C and 7"C, without affecting the organoleptic quality. Pearce (1943) reported similar findings from his storage studies covering a temperature range of -40" to 24°C.


TABLE LIII CHANGES IN ACIDITY O F VACUUM-PACKED GERM STORED AT DIFFERENT

TEMPERATURES~

Aridity (as % H, SO,) at:

Storage period (days) 0" c I" c 22°C 29°C 35°C

0 0.126 31 0.157 61 0.160 99 0.140

126 0.183 162 0.249 196 0.213

0.00044b

0.126 0.165 0.208 0.150 0.193 0.269 0.244 0.00060b

0.126 0.203 0.257 0.270 0.333 0.462 0.500 0.00 191

0.126 0.229 0.330 0.360 0.445 0.546 0.638 0.00261b

0.126 0.3 25 0.462 0.590 0.770 0.808 0.993 0.00442b

aSherwood et al. (1933). bAverage daily increase in acidity.

Fitfield and Bailey (1929) observed a similar acidity-temperature relationship for stored flours of different extraction rates. When the observations made by Sherwood et al. (1933) are compared with those of Fitfield and Bailey (1929) and Markley and Bailey (1931), it is seen that the daily increase in acidity under similar storage conditions was four times as fast in wheat germ as in patent flour.

3. Effect of Moisture

Using different solvents for the extraction of lipid, Sullivan and Near (1933) estimated the acidity and the nitrogen and phosphorus contents of lipids in samples stored in glass containers for 6 months. The acidity of the stored germ depended on its moisture level (Table LIV). The acidity (1.27% on H2 SO4) of the germ stored at 12.3% moisture was higher than that of the germ stored at 4.3% moisture. On storing the germ in airtight glass containers and cotton bags, they found that the sealed glass container retained the original moisture content, while the germ stored in bags lost considerable moisture (5.5%) through evapora- tion. Pearce (1943) studied the stability of the germ at different moisture levels ranging from 8.0 to 26.5% and observed an increased shelf life for the germ when it was stored at a low moisture level. Cuendet et al. (1954) found that the germ developed an undesirable odor within 6 weeks even when it was stored at a moisture level of 3% in a closed glass jar, They also reported that the development of acidity in the various mill fractions was directly proportional to their lipid contents. After a one-year storage period, the acidity of the germ containing 12.9% lipids was about 2.0%, whereas that of patent flour with 1.3% lipids was as low as 0.03%.

WHEAT GERM 26 1

TABLE LIV

EFFECT O F STORAGE O F GERM AT DIFFERENT MOISTURE LEVELS ON

L I P I D CONSTITUENTS'

6 months of storage at: ~~ ~

Initial 12.3% moisture 4.3% moisture

Eb Pc Nd Eb f Nd Eb p' Nd Solvent used (%) (%) (%I (70) (%) (5%) (70) (70) (%)

Alcohol-ether 15.62 0.50 0.41 12.81 0.30 Trace 13.68 0.560 0.35 Ether 11.81 0.14 0.12 13.00 Trace 0.04 11.54 0.085 0.04 Acetone 12.58 0.13 0.34 14.60 0.04 0.05 12.23 0.094 0.23

'Sullivan and Near (1933). bExtractives. 'Phosphorus. dNi trogen.

Sullivan and Near (1933) found that germ samples stored at a higher moisture content showed a marked decrease in the alcohol-ether extractives, and an increase in the ether or acetone extracts. This was due to the solubility differences of lecithin and its split products-that is, fatty acids, choline, and glycerophos- phoric acid. The nitrogen and phosphorus contents also decreased in all the extractives. Storage at low moisture levels showed relatively slight changes in germ lipids. The changes observed were explained as being due to enzyme hydrolyses and were correlated with increasing moisture and acidity of the samples.

4. Causes of Spoilage

Rancidity and peroxide values in germ oil increased concurrently during storage, whereas in whole germ the rancidity was detectable even when the peroxide values were relatively low (Pearce, 1943). As such, the peroxide value was found to be a better index of spoilage for the oil than for the germ. It was therefore suspected that protein may be mainly responsible for spoilage of the germ, rather than lipids as reported by Sherwood er al. (1933). Pearce (1943) confirmed this by estimating the fluorescence of potassium chloride extract of defatted wheat germ (Table LV). The fluorescence was attributed to the products of protein hydrolysis. The results of both Sherwood er al. (1933) and Pearce (1943) were confirmed by Lusena and McFarlane (1945).

Yakovenko (1961) reported that microorganisms did not play a decisive role in the development of rancidity in the germ. He observed in stored germ an increased lipoxidase activity which was dependent on the temperature of storage. Maximum lipoxidase activity was observed during 6 months of storage at


TABLE LV FLUORESCENCE OF 10% POTASSIUM CHLORIDE EXTRACT O F

DE FATTE D w H EAT GERM'

Fluorescence reading Condition of germ in photofluoronieter

Fresh Storcd for 6 months at:

-4O.O"C -17.8"C - 9.4"C - 1.1"C 15.6"C

11.0

11.6 11.8 12.4 12.2 14.0

'Pearce (1943).

16" to 21°C. The results indicated a correlation between lipoxidase activity and the development of off-flavors in the germ.

According to Rothe and Stoeckel (1962) and Rothe (1963), both lipase and lipoxidase activities in the germ were responsible for the development of off- flavors during storage. Stability of the germ was increased by reducing the lipase and lipoxidase activities. Rothe (1963) found that lipase activity decreased rapidly as germ moisture was reduced to 4.5%. Below this moisture level, no lipase activity was detected. Further, he observed a considerable increase in the fatty acid content of four germ samples stored over a period of 5 weeks at room temperature. From the initial values ranging from 50 to 90 mg, the fatty acid values increased to a range of 185 to 280 mg. This increase resulted in products of varying degrees of bitterness.

Later, Rothe er al. (1967) reported that oxidation of fat was the main reason for the development of off-flavors in the germ. According to them, fat is converted to hydroperoxides either by autoxidation or by an enzymic reaction mainly by lipoxidase. Normally the lipoxidase reaction was faster than autoxidation. The hydroperoxides could be further oxidized to polymerized compounds, which impart a bitter taste, or t o carbonyl compounds, which give a rancid taste to stored germ.

5. Evaluation of Freshness

Sherwood er ul. (1933) and Sullivan and Near (1933) used alcoholic acidity as the criterion for assessing the spoilage of the germ during storage. Estimation of fluorescence resulting from products of proteolytic activity was used by Pearce (1943). Yakovenko (1961) found lipoxidase activity to be a measure of freshness. In the studies of Rothe (1963), free fatty acid formed the basis of germ

WHEAT GERM 263

TABLE LVI

RELATION BETWEEN DECANAL VALUE AND RANCIDITY

IN GERM‘

Organolep tic Sample qualityb

Decanal value Peroxide (mg%) valueC

1 2 3 4 5 6 7 8 9

10 1 1

- Slightly bitter

Bitter Bitter

+ +

++ ++

+++ +++ +++

1.4 0.8 1.4 2.1 3.8 4.2 4.2 5 .1 6.6 7.4

17.0

0 3 1 1 4

10 4

1 1 1 1 22

7

‘Rothe et a!. ( 1 967). b- satisfactory, + rancid, ++ highly rancid, +++ unacceptable. ‘Determined according to the method of Franzke (1956).

stability. Lusena and McFarlane (1945) found a peroxide value of 20 meq/kg of the germ as the threshold value, beyond which the rancidity could be detected by smell and taste. They, however, did not find any relation between lipoxidase activity and subsequent peroxide formation during storage.

According to Rothe el al. (1967), the “decanal value” is a good measure of germ freshness. The method for determination of the decanal value consisted in steam distillation of germ fat, formation and separation (by thin-layer chromatography) of hydrazones, and measurement of absorbance of aldehydes of higher chain length. From the results presented in Table LVI, it was inferred that the decanal value was better correlated to rancidity than the peroxide value. The critical decanal value without detectable rancidity was found to be 3 mg per 100 gm of germ. Further, there was a steady increase in the decanal value which could be better correlated with the organoleptic acceptability of stored germ. On the contrary, peroxide values showed an irregular increase or decrease during the storage period.

B. METHODS OF STABILIZATION OF WHEAT GERM

It is evident from the work of Sherwood et al. (1933) and of Pearce (1943) that raw germ on storage develops a rancid flavor and bitter taste in a short time. Rothe (1963) has observed that, because of the high enzyme activity and

264 S. R . SHURPALEKAR A N D P. HARIDAS RAO

unsaturated fat content in fresh germ, the organoleptic acceptability is affected adversely within a few days.

The poor stability of raw germ has restricted its food uses; this problem could be overcome either by inactivating the enzymes or by creating conditions unfavorable for the enzymic activity by suitable means. Some of the important methods for stabilization of the germ and the effect of different treatments on the enzyme activities are discussed below:

1. Heat Processing

Light toasting of the germ at 120" to 130"C, until it attained a light brown color, improved its keeping quality as well as its palatability (Hertwig, 1931). The germ thus heated and stored in a glass jar at 50°C remained fresh even after 25 days of storage. When stored in paper cereal cartons at room temperature, the toasted germ was in good condition even after 10 months of storage.

Lusena and McFarlane (1945) studied the effect of heating the germ, at various moisture levels for different periods in a hot air oven, on the enzyme activities and its stability during storage at 37°C (Table LVII) in laminated metal foil. They found that all the heat treatments completely destroyed lipoxidase activity; the proteolytic activities were reduced considerably, depending on the moisture level. The enzyme-active raw germ samples showed an unexpectedly smaller increase in peroxides compared with the heat-treated samples. All the samples developed strong off-flavors during 5 weeks of storage.

As the germ with low moisture content showed less tendency to develop off- flavors in storage, Lusena and McFarlane (1945) subsequently treated raw germ with moist heat followed by dry heat. The treated samples packed in cellophane envelopes were in good condition even after a month's storage at 55°C. It is interesting to note that the peroxide values of both the control and the heat-treated samples were comparable after a month of storage.

The other method of stabilization developed by them was direct steaming of the germ in a chamber at 110°C for 30 minutes and then drying it at 100°C under nitrogen.

Wierszbowski et al. (1966) stabilized the germ by heat treatment at 240°C for 2 minutes. They observed a decrease in the amylolytic and proteolytic activities as a result of a reduction in the number of -SH groups. Due to heat treatment, reduction in -SH groups as determined by amperometry has also been reported by Swatditat (1974).

Rothe (1963) carried out investigations on the possible ways of stabilizing wheat germ, either by inactivation of the enzyme by heat treatment or by a drying technique to create conditions unfavorable for enzyme activity. Moisture and dry heat were utilized to improve the keeping quality of the germ by inactivating the lipolytic enzymes responsible for the bitter taste,

TABLE LVII

EFFECT OF VARIOUS HEAT TREATMENTS AND SUBSEQUENT STORAGE CONDITIONS ON ENZYME ACTIVITY AND PEROXIDE

FORM AT ION^

Heat treatmentb

Sample Duration System Storage atmosphere Moisture (%)

Lipoxidase Proteolytic activity activity

(units/kg) (units/kg)

Peroxides formedC

Initial 7 days 14 days 35 days

1.5 hours A.C.d 1.5 hours A.C. 1.5 hours N.C.e 1.5 hours N.C. 12 hours A.0.f 12 hours A.O. Control-untreated Control-untreated

Air Nitrogen Air Nitrogen Air Nitrogen Air Nitrogen

10.3 9.6 8.6 9.7 0.9 0.9

1 1 . 1 11.1

Nil Nil Nil 20 Nil 23 Nil 16 Nil 35 Nil 35 537 42 537 42

Nil Nil Nil Nil 1.0 1.0 Nil Nil

0.2 0.1 Nil Nil

20.0 10.1 Nil Nil

~ ~

1.2 20.3 1.5 23.4 0.9 10.0 0.9 5.3

39.0 43.0 54.7 60.0

0.4 16.0 0.3 14.3

'Lusena and McFarlane (1945), bAt 100°C. 'Expressed as milliequivalents per kilogram of oil during storage at 37°C. dAir-covered. 'Ni trogen-covered. fAir open.


Interesting data regarding the effect of moisture content and temperatures of heat treatment on the lipase activity are presented in Table LVIII. The lipase of the germ containing 12% moisture was found to be quite stable when the germ was heat-treated at 70°C for 24 hours. It could be concluded from the data that, as the moisture content increased at a given temperature of heat treatment, the extent of inactivation also increased. Further, at the same moisture content, the degree of inactivation increased with the increase in the temperature of the heat treatment.

Rothe and Stoeckel (1967) studied the effect of a 20-hour heat treatment on lipoxidase and peroxidase activities of wheat germ containing 6.3% moisture. Based on the data collected, a linear equation to correlate the inactivation temperature of the enzyme and the moisture content of the germ has been worked out, and correlation coefficients of 0.990 for peroxidase and 0.998 for lipoxidase have been obtained. Rothe and Stockel (1967) further reported that, on a dry-weight basis, the inactivation temperatures of peroxidase and lipoxidase were 108°C and 67"C, respectively.

According to a U.S. patent (1974), the stabilization of wheat germ could be carried out by (i) grinding in an impact mill, (ii) suspending the ground germ in air and heating to about 93°C to lower the moisture content to less than 6%, and (iii) collecting in a cyclone and sifting to remove bran particles.

Ivanova et ul. (1975) conducted extensive studies on the heat stabilization of wheat germ by using hot air-stream at 80-1 10°C or steam heating at 0.5-1.75 atmospheres followed by hot air stream drying at 100"-120°C. Drying in a hot air stream at 100°C was found to be a most promising treatment. Heating at

TABLE LVIII

EFFECT OF MOISTURE CONTENT ON HEAT SENSITIVITY' OF

WHEAT GERM L I P A S E ~ . ~

Loss in enzyme activity (%) at :

Moisture content (%) 100°C 90°C 80°C 70°C

4 1 0 0 0 9 55 21 0 0

12 100 15 15 0 16 100 100 53 10 19 100 100 60 28 25 100 100 100 75

'Expressed as loss in enzyme activity (%). bEstimated according to Rothe (1961). 'Rothe (1963).

WHEAT GERM 267

100°C for 8 minutes resulted in reduction of moisture from 12.67 to 2.90%. Such a sample could be stored in good condition for about 90 days without any change in its vitamin E content. Only small increases in acid and peroxide values were observed. Heating at 100°C for 3-4 hours facilitated preseving wheat germ without any change in acid value. A moisture content of 3.0-3.5% was considered to be critical for wheat germ stabilization.

2. Ethylene Dichloride Treatment

“Tonic” wheat germ, which is a fat-free residue obtained by extraction with ethylene dichloride, has been reported to have good keeping quality (Lusena and McFarlane, 1945). Even though the germ treated with ethylene dichloride stored well for one and one-half months at 55”C, removal of traces of the solvent was a problem. Lusena and McFarlane (1945) found that steaming of the treated germ removed all the residual solvent. Consequently, a process combining both the ethylene dichloride and the steam treatments has been developed by them. A product thus treated had 4.7% moisture and was free of lipolytic or proteolytic activity. Further, the product was quite palatable and retained its freshness for 8 months when stored in cellophane envelopes at 37°C. Untreated germ, however, developed an off-flavor at the end of one month’s storage.

3. Infrared Heat

Maes and Bauwen (1951) reported that stability of the germ could be increased by subjecting it to infrared radiation. The stability was dependent on the radiation period, the intensity of the radiation, and the thickness of the germ layer exposed. The acidity of the germ, which reflected the freshness, was much higher in stored raw germ than in treated germ.

4. Treatment with Epoxy Compounds

Gaver (1962) patented a process for improving the shelf life of wheat germ by treating it with epoxy compounds. In addition to enhancing its stability against fermentation, rancidity, and discoloration, such treatment also resulted in a germ of improved flavor.

The method involved exposing fresh wheat germ in an air-free anhydrous container to a mixture of epoxy compounds consisting of ethylene oxide and propylene oxide until the resulting wheat germ contained about 2 to 5% by weight of reacted epoxy compounds. The treated germ was quite stable when stored for 5 months at room temperature or at 100°F.


5. Deoiling, Alkali Treatment, and Roller Drying

Grandel (1959) in his patent has described a method for stabilizing and debittering the germ. The steps involved were: (1) deoiling in a hydraulic press until the germ contains less than 4% oil; (2) grinding the deoiled germ in a roller mill, so that the degree of comminution does not exceed 50% (this avoids contamination with bran, containing bitter compounds); (3) treating the fine flour with water containing the requisite amount of sodium carbonate or bicarbonate, corresponding to the acidity of the germ flour; (4) and flaking the germ slurry on a roller dryer at 130" to 140°C.

6. Treatment with Antioxidant

Barnes (1948) reported that addition of 5-pentadecylresorcinol at a level of 0.01 to 0.5% to wheat germ enhanced its shelf life by inhibiting the oxidation of germ fat. The germ treated at a 0.2% level did not show any rancidity even after 75 days of storage, whereas raw germ developed a rancid taste in only 17 days.

7. Lowering the Moisture Content

By a simple drying technique, Rothe (1963) has reported that the lipase activity of 100% observed in germ samples containing 26.5% moisture decreased steadily to complete inactivation, when the moisture content was reduced to about 4%. The data on the relationship between the lipase activity of the wheat germ and its dependence on moisture content are presented in Fig. 12. A drying technique has been developed by Rothe (1963) for stabilizing the germ by reducing its moisture content to 5%. This is presented schematically in Fig. 13.

Moisture content during enzyme reaction (%)

FIG. 12. The relationship between inactivation of germ lipase and its moisture content.

WHEAT GERM 269

In let I n l e t

A i r o u t l a

r in le t

g e r m

watad duct

Outlet

FIG. 13. Schematic presentation of apparatus for drying of wheat germ.

Hot air is allowed to enter the chamber from the bottom, and it leaves at the top after carrying away the moisture from the germ sample falling through metallic wire mesh from top to bottom. He has also worked out a process for drying wheat germ to a 5% moisture level by using predried air at temperatures below 35°C. In this way the germ sample can be stabilized without affecting the nutritive components like vitamin E and thiamine and some of the desirable enzymes as well as the fresh taste. Wheat germ thus treated and packed in moisture-proof containers showed no undesirable changes even after two and one-half years of storage.

The keeping quality of the germ in relation to its moisture content, when stored at room temperature in diffused daylight, has been studied by Rothe (1963). The data presented in Table LIX highlight the good keeping quality of the product stored for more than 600 days at a moisture content of 5%. In contrast, in germ samples containing 13% moisture, the onset of bitterness or stale taste was observed in a short period of 3 days.

TABLE LIX EFFECT OF MOISTURE CONTENT ON KEEPING QUALITY

OF WHEAT GERM'^^

Moisture content

(%)

Storage period until onset of astringent or bitter taste

(days)

13 9 6 5

3 21 60

6 00

'Rothe (1963). bStored at room temperature in diffused light.


8. Miscellaneous Treatments

Donk and MacDonald (1935, 1937) patented a method of stabilizing wheat germ against rancidity, Finely ground germ flour was mixed with sodium chloride to absorb moisture. It was then blended with nonfatty, starchy materials like potato flour or rice flour and dried under a current of nitrogen or carbon dioxide.

Musher (1940) stabilized the germ against oxidative deterioration by dispersing it with aqueous skimmed milk and heating it to at least 170°F prior to drying.

C. EFFECT OF STORAGE AND STABILIZATION ON THE NUTRIENTS

Hove and Harrel (1943) reported that toasting wheat germ to make it suitable for human consumption improved its keeping quality without affecting its nutritive value. According to Pearce (1943), the thiamine content of the germ, when stored for 6 months at 15.6"C in sealed containers, remained unaffected. Wierszbowski et al. (1966) observed a loss of tocopherols during storage of the germ. On the contrary, lusena and McFarlane (1945) had found earlier that both thiamine and tocopherols in germ samples packed in cellophane bags were quite stable during the stabilization process as well as after 8 months of storage

TABLE LX

GLUTATHIONE CONTENT OF RAW AND TREATED WHEAT

GERM^

Glutathione content (md100 gm)

Oxidized Sample Total Reduced (by difference)

Raw germ 147.4 102.6 44.8 Treated germ

Steamed at 105-110°C for 30 79.8 80.5 Ni 1 minutes; finally air-dried at 100°C for 1 hour

dichloride vapor;b finally air-dried at 100°C for 1 hour

Exposed to ethylene 76.7 77.2 Nil

'Lusena and McFarlane (1945). bAt 95" to 100°C for 15 minutes followed b y 15 minutes of steaming

at 105" to 110°C.

WHEAT GERM 21 1

at 37°C. They also reported that different treatments for stabilizing the germ destroyed 50% of the total glutathione (Table LX). The reduced glutathione decreased by 25%, while the oxidized form was completely destroyed.

Cuendet et al. (1954) observed that the moisture content at which wheat germ was stored had a profound effect on the loss of thiamine (Table LXI), which was greater in the samples containing higher moisture levels. During 3 weeks of storage, little loss of thiamine was found, whereas after 52 weeks, 80% of the original thiamine in the germ was lost. The thiamine content of the germ having 3% moisture remained unchanged during storage.

Iwata ef al. (1955a) inferred that the loss of thiamine in raw germ during storage was proportional to the degree of germ damage. The loss of riboflavin in the germ, when stored either at 37°C or at room temperature, was relatively stable, while loss of pyridoxine was observed mainly at higher temperatures of storage.

Rothe (1963) studied the effect of storage of differently processed germ products from some European countries on the taste, fat acidity, vitamins, and linoleic acid contents. The data presented in Table LXII highlight clearly the effects of dry and moist heat. Different methods of processing were found to preserve the organoleptic quality and nutrients of the germ samples to different degrees. It is evident from the data that the thiamine and vitamin E contents of product 1 stabilized by dry heating and were significantly lower than the contents of products 2 to 5 processed by moist heat treatments. However, fat acidity was relatively lower for product 1, as compared with products 2 to 5 . The linoleic acid contents of different products were comparable within a range of 43 to 50% on the basis of fat. Organoleptically, dried germ was more acceptable over a longer period of 33 months, as compared with products 1 to 5, which showed different degrees of staleness, bitterness, etc., during 8 months of storage.

TABLE LXI EFFECT O F MOISTURE ON THIAMINE CONTENT OF GERM

DURING STORAGE AT 37.8"Ca

Thiamine content (rng/lb)b after storage for:

Moisture content (%I 0 week 3 weeks 38 weeks 52 weeks

3 10.1 11.3 8.8 10.1 6 11.2 11.2 8.8 9.4

10 10.8 10.4 8.5 8.0 14 - 10.5 4.8 2.1

'Cuendet ef al . (1954). bOn a dry basis.

TABLE LXII QUALITY PARAMETERS OF STORED WHEAT GERM PRODUCTS~

Method of Storage period Fat acidityb Thiamineb Vitamin Eb Linoleic acid Products stabilization (months) Taste (mgKOH) (vg) (mg) (%in fat)

Fresh wheat germ - 0 Fresh 4Cb100 1500-2500 15-30 4 2-5 2 Dry wheat gerp Drying 33 Fresh 120 1780 19 43

Product 2 (GDR)‘ Moist heat 8 Somewhat bitter 216 1640 18 45

Product 4 (Austria) Moist heat 8 Somewhat stale, bitter 196 2100 22 44 Product 5 (Switzerland) Moist heat 8 Irritating, bitter 290 1670 20 50

Product 1 (GDR)C Dry heat 8 Slightly stale, somewhat bitter 153 970 1 3 48

Product 3 (FRQd Moist heat 8 Rusty, somewhat stale 180 1870 21 46

‘Rothe (1963). bper 100 gm of dry matter. ‘German Democratic Republic. dFederal Republic of Germany.

WHEAT GERM 27 3

D. SUMMARY

Freshly milled raw germ is highly unstable and deteriorates rapidly within a few days, as it is rich in enzymes, lipase, lipoxidase, and protease. Different studies have indicated that the keeping quality of the germ is dependent on moisture content, temperature and period of storage, mode of packing (inert gases or vacuum), processing treatment, etc. Storing at low moisture of about 5% and low temperatures (less than 10°C) or packing under inert gases or vacuum enhances the shelf life of the germ significantly.

Oxidation of fat was one of the main factors contributing to spoilage of the germ during storage. Among different indices such as alcoholic acidity, free fatty acids, peroxide value, and the decanal value used for evaluating the quality of the germ during storage, the decanal value has been claimed to be the best. Many methods such as dry or wet heat processing, or treatment with ethylene dichloride, epoxy compound, infrared heat, antioxidants, sodium chloride or skim milk powder, alkali, etc., or lowering the moisture content have been employed by several workers for stabilization of the germ. The principle governing the stabilization of the germ for improving its shelf life is the inactivation of enzymes. Of these methods, only heat processing appears to be practically feasible on a commercial scale. The stability of different nutrients, mainly vitamins, during storage is dependent on the processing methods employed for stabilization and the storage period.

VII. WHEAT GERM AND BREAD-MAKING QUALITY

Exhaustive literature is available on the effect of the use of wheat germ in bread making. Several workers have drawn different conclusions about the beneficial as well as the adverse effects of the germ and its components on dough characteristics and bread-baking quality. Various methods to overcome the deleterious effects on baking quality have been suggested.

A. EARLIER STUDIES

The constituents in the germ responsible for deleterious or beneficial effects on bread-making quality have been studied by several workers. Consequently, different theories have been put forth to clarify the roles played by these constituents. Various treatments have been suggested to counteract or overcome the adverse effects.

Some of the factors-germ constituents or processing conditions-possibly influencing baking quality are discussed below.


1. Phosphatides

Geddes (1 930) reported that germ added to fifth-middlings flour significantly reduced its baking quality, as reflected by (1) the poor handling property of the dough, (2) poor loaf volume, and (3) poor crumb characteristics. Addition of bromate to the dough or heating the germ before blending i t with the flour reduced the deleterious effect of the germ. He suspected that oxidation of phosphatides present in the germ was the primary cause of such improvement. However, this was disproved later by Rich (1934), who reported that some germ constituents other than phosphatides were responsible for the adverse effect on baking quality.

2. Glutathione

From farinograph data and baking trials using fresh as well as stored germ, Sullivan et al. (1936a,b) observed that some beneficial changes took place in the harmful constituents during storage of the germ (Table LXIII), They also found that the harmful constituent was water-soluble. Later, Sullivan el al. ( 1 9 3 6 ~ ) suggested that glutathione was probably the harmful constituent of the germ. By using the Sullivan test (Sullivan and Hess, 1931), they detected glutathione in the water extract of the germ. This was confirmed by their findings that incorporation of 60 mg of pure isolated glutathione or water extract from 10 gm of germ in the bread recipe had a similar adverse effect on the balung quality (Table LXIV). Bull (1 937) reported that baking quality was not impaired when the coagulable fractions were removed from the water extract of the germ by heating or dialyzing.

According to Sullivan et al. (1 937), glutathione activated the proteolytic enzymes, which in turn influenced the gluten quality adversely. The beneficial effects of heat treatment of the germ or addition of oxidizing agents such as

TABLE LXIII

EFFECT OF GERM INCORPORATION ON BAKING QUALITY OF PATENT FLOUR"

Sample Dough quality Loaf volurneb

Patcnt flour (PF) Strong, elastic 100 PF + 10% fresh germ (untreated) 61 PF + 10% fresh germ (ether-extracted) 62 PF + 10% stored germC Poor, soft 66

Very poor, soft, short, sticky Very poor, soft, short, sticky

'Sullivan el al. (1936b). bCalculated on the basis of 100 for bread loaf from 100 gm of patent flour containing

CFor 10 months at 13% moisture. 13% protein.

WHEAT GERM 215

TABLE LXIV EFFECT OF GERM GLUTATHIONE ON BAKING QUALITY OF PATENT FLOUR"

Form of glutathione added Dough quality Loaf volumeb

Patent flour (PF) Strong and elastic 100 PF + water extract from 10% fresh wheat germ PF + 60 rng glutathione from germ PF + 60 mg glutathione from yeast

PF + 10% fresh germ + 60 mg potassium bromate

Very poor, very soft 15 Poor, soft, sticky 19 Poor, soft and sticky 15

Fair plus 89 PF + 10% fresh germ Poor, soft, dead 12

"Sullivan et al. (1936~). bCalculated on the basis of 100 for bread loaf from 100 gm of patent flour.

potassium bromate (Sullivan et ul., 1936c) or lactic acid (Zav'yalov, 1939, 1940) were found to overcome the adverse effects of the germ on baking quality. This was attributed to the oxidation of reduced glutathione to an oxidized form.

3. Fermented Germ

Hullett and Stern (1941) found to their surprise that the harmful effects of the germ on baking quality were no longer observed when a pre-ferment consisting of wheat germ, water, and yeast was used in bread preparation. The reduced glutathione was not detected in the pre-ferment, as indicated by the sodium nitroprusside reaction. However, when boiled germ was used in the pre-ferment, reduced glutathione could be detected. These observations indicated that destruction of glutathione in the germ was connected with an enzyme mechanism effective in the raw germ and not in the boiled germ. Therefore, they did not believe that reduced glutathione (-SH) was converted to the oxidized form ( S : S ) during heating, as suggested by Sullivan et ul. (1937). Further, a minimum of 6 hours of pre-fermentation was required to overcome completely the deleterious effect of the germ on the baking quality. An increase in the temperature (up to 35'C) and in the quantity of yeast and a decrease in the initial pH to 5.0 to 5.5 shortened the pre-fermentation time required for destroying glutathione.

Using blends of varying percentages of wheat germ and hard red spring wheat flour, Smith and Geddes (1942) made an interesting observation that the dough-handling qualities and loaf characteristics improved as the fermentation time increased from 1.5 to 4.5 hours. The inclusion of potassium bromate in the bread formulation brought about a spectacular improvement in both the dough- handling properties and the loaf characteristics. These workers also found an improvement in the baking quality when the germ was allowed to stand in an aqueous suspension containing 80 mg of potassium bromate per 100 gm of germ. On the other hand, pre-fermentation of the germ with yeast progressively


decreased the harmful effect, depending on the time of fermentation up to 4.5 hours. Inclusion of potassium bromate in this pre-ferment further improved the baking behavior. However, the improvement was more prominent when bromate was added at the dough stage. Under optimum conditions of fermentation time and bromate level, bread baked from patent flour containing the germ was comparable to the quality of control bread based on patent flour alone. The higher efficiency of the bromate, when added to fermenting germ-flour dough rather than to the pre-ferment, indicated that the potassium bromate exerted a direct action on the gluten protein and not on the glutathione, as suggested by Sullivan et al. (1937). In contrast, Elion (1943) observed from his experiments that the beneficial effect of the oxidizing agents was due mainly to the oxidation of glutathione and not to their action on gluten. However, he also found an improvement in the baking quality of bread containing the germ with an increase in fermentation time. He confirmed the earlier findings (Smith and Geddes, 1942) regarding the deleterious effect of wheat germ which was attributed mainly to the activating effect of reduced glutathione on flour proteinases.

Stern (1944) did not find any evidence to prove that the deleterious effect of germ glutathione on bread quality was due to the activation of proteolytic enzymes in the flour. He suspected direct action of the glutathione on the gluten itself. The better characteristics of the dough made with fermented germ were explained by the absence of -SH groups. According to him, the enzyme responsible for the elimination of the -SH groups in fermenting dough was a dehydrogenase of the germ, the presence of which was demonstrated by them.

The adverse effect of fermented wheat germ on bread quality, when used at hgh levels, was also reported by Greer et al. (1953). They observed the formation of an undesirable pink or reddish brown discoloration, both in the germ ferment and in the bread crumb, whenever fermentation of the germ was unduly prolonged. From fermented germ, they isolated methoxy-y-benzoquinone, which acted as a bread improver. They suspected that the improving action of the fermented germ was due to the benzoquinone derivative and not to the oxidation of glutathione, as earlier workers suggested (Hullett and Stern, 1941; Smith and Geddes, 1942).

4. Steeping of the G e m

According to Grewe and LeClerc (1943), steeping the germ considerably improved its bread-malung properties. The beneficial effect of steeping increased progressively with time up to 8 hours. The addition of potassium bromate during steeping of the germ resulted in further improvement in bread quality. These findings were similar to the earlier observations of Hullett and Stern (1941). However, they inferred that steeping in water itself counteracted the adverse

WHEAT GERM 211

effect of glutathione, and the presence of yeast in the pre-ferment was not essential, as observed by Hullett and Stern (1941).

Interestingly enough, Grewe and LeClerc (1943) found that addition of steeped germ at a level of 2.5% or 5% to flour produced bread that was even better than the control bread based on flour alone. Further, steeped germ up to 10% could be added to the flour dough, without any detrimental effect on the loaf quality. Use of even 15 to 20% levels of steeped germ produced acceptable bread, which was only slightly inferior to the control bread. Addition of salt (in amounts normally used in bread making) to the germ during steeping brought about an improvement in the handling property of the dough. This improvement was due to the change in the colloidal properties of the germ as measured by its viscosity.

B. RECENT STUDIES

In recent years only a few workers have studied the roles played by germ constituents, by the processing of the germ, and by additives in bread quality.

1. Effect of Processed Germ

Pomeranz et al. (1970b) and Giacanelli (1973) have demonstrated qualitatively and quantitatively the effect of the inclusion of wheat germ components on bread quality. According to them, the unfavorable influence of certain components on the baking process could be eliminated by heat treatment.

a. Processing of the Germ. Processing of the germ as carried out by Pomeranz et al. (1970b) consisted in the following operations: (1) heating the germ having 14.9% moisture for 8 hours at 80°C; (2) subsequent drying to about 4% moisture; (3) extracting the lipids with petroleum ether; and (4) grinding the extracted germ in a Hobart mill and re-extracting with petroleum ether.

b. Inactivation of Glutathione. The inactivation of glutathione (Pomeranz el al., 1970b) during heat treatment was found to be dependent on the temperature and moisture content of the germ (Fig. 14). For the germ containing 14.9% moisture, the inactivation time at 60°C was nearly four times that of the germ containing 23.7% moisture. However, this difference was less pronounced at higher temperatures of heat treatment.

c. Effect on Dough Characteristics and Loaf Volume. The effect of the addition of raw and heat-treated germ on loaf volume (Pomeranz el al., 1970b) is shown in Fig. 15. The loaf volume decreased with the increase in levels of raw germ. The volume of the bread made by incorporating heat-treated germ was consistently higher than that of the bread containing raw germ. It was interesting to note that no decrease in loaf volume was observed even in bread containing

27 8 S. R. SHURPALEKAR

900 c 950 - - E - 850- z - 5

60 80 100

Temperature ("C)

-

AND P. HARIDAS RAO

H E Y T R E A T E D

-0 4:- CONTROL \

0 5 10 15

Germ level (%)

FIG. 14 (left). The effect of temperature and moisture on inactivation time ofglutathione in the germ.

FIG. 15 (right). The effect of the addition of raw and heat-treated germ on loaf volume.

15% of heat-treated germ. The addition of heat-treated germ to the flour also increased farinograph water absorption by approximately 1% per gram of germ. Further, mixing time decreased in germ-enriched doughs, depending on the level of germ addition.

d, Effect of Bromate. In contrast to the requirement of only 10 ppm of bromate for the control bread, a very high level of 70 ppm was required in doughs containing 15% of heat-treated germ. The bromate requirement was even higher when raw germ was used. However, the addition of bromate did not eliminate completely the deleterious effect of raw germ.

TABLE LXV EFFECT OF HEAT-TREATED GERM AND POLAR LIPIDS OF

WHEAT FLOUR O N LOAF VOLUME OF BREAD^ ~

Heat-treated germ Polar lipids Loaf volume (%o) (%) (ml)

0 5 5

10 10 15 15 15 15

0 0 0.2 0 0.4 0 0.8 1.0 2.0

864 890 900 895 930 885 925 945 95 5

-~ ~

'Pomeranz et al. (1970b).

WHEAT GERM 27 9

TABLE LXVI EFFECT OF LECITHIN ON LOAF VOLUME OF BREAD BAKED WITH

HEAT-TREATED GERM'

Germ added (%)

0 5

10 15 20 30

Loaf volume (ml) of bread baked with lecithin levels of:

0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0% 4.0% 6.0%

864 855 878 870 865 855 865 -

890 925 945 935 - - - 895 940 943 1010 973 - 985 - -

885 920 918 940 975 940 - - -

865 - 915 - 920 - 915 900 - 818 - 845 - 840 - - 855 820

- -

aPomeranz et al. (1970b).

e. Effect of Polar Lipids. The addition of free polar flour lipids was found to improve the loaf volume of bread containing the germ (Pomeranz et a l , 1970b), as seen in Table LXV. The increase in the loaf volume of bread containing 15% of heat-treated germ was dependent on the level of polar lipids added. On an equiprotein basis, the volume of bread baked with a sodium chloride extract of germ was higher than that of bread baked with heat-treated germ. A similar beneficial effect of polar lipids on the baking quality of wheat flour with or without the germ has been confirmed by Daftary et al. (1968) and by Bolling et al. (1973).

As polar lipids contain both phospholipids (lecithin) and glycolipids, Pomeranz et al. (1970b) also studied the effect of incorporation of only phospholipids isolated from soybean on the loaf volume of germ bread. The addition of soya

750 9

I 1

0 1 2 3

Lecithin (%I

FIG. 16. The effect of lecithin addition on loaf volume of bread baked with 0%, 3%, 6%, and 9% of a sodium chloride extract of germ products.


TABLE LXVII EFFECT OF VARIOUS PHOSPHOLIPIDS O N LOAF VOLUME OF

BREAD‘

Loaf volume (ml) of bread bakedb with phospholipid levels of:

Lipid 0% 1% 1.5% 2%

None (control) Polar, weight flour Soya lecithin DL-cY-Lecithin D L-ol-Cephalin Phosphatidyl ethanolamine Phosphatidyl serine Inositol phosphatide

71 81 78 79 72 75 75 83 86 88 71 70 72 81 84 86 74 72 75 86 86 90

‘Pomeranz et al. (1 970b). bFrom 10 gm of flour and 1 gm of germ.

lecithin significantly improved the loaf volume of bread baked with up to 30% of heat-treated germ (Table LXVI). The optimum level of lecithin increased with an increase in the levels of germ added. In bread containing 10 to 30% of wheat germ, the loaf volume was the highest when the lecithin-to-germ ratio was between 1 : l O and 1.5:lO.O. The addition of a small amount of sucrose mono- myristate was found to counteract the defect of coarse crumb structure, observed as a result of using lecithin in germ-enriched bread. The effect of lecithin levels on the loaf volume of bread baked with various levels of sodium chloride extract of germ is given in Fig. 16. Bread baked without any germ extract did not show any improvement on addition of lecithin.

The effect of various types of synthetic phospholipids on the loaf volume of bread baked from 10 gm of flour and 1 gm of heat-treated germ is given in Table LXVII. DL-ar-Lecithin was found to be a better improver than soya lecithin. Synthetic DLff-cephalin (a phosphatidyl ethanolamine) had no improving effect. In contrast, phosphatidyl ethanolamine of soybean was an excellent improver. Phosphatidyl serine had very little effect on the loaf volume of germ bread, whereas inositol phosphatide was found to be an excellent improver. These variations in the beneficial effect of phospholipids were suspected to be due to the difference in the fatty acid composition of various phospholipids.

2. Effect of Germ Lipids

Bolling et ul. (1973) carried out experiments to investigate the contradic- tory conclusions regarding positive (Rohrlich and Schoenmann, 1962) and

WHEAT GERM 28 1

TABLE LXVIII EFFECT O F WHEAT GERM AND WHEAT GERM OIL O N L O A F VOLUME OF BREAD

BY RAPID MIX T E S f

Level of addition

Germ Germ oil

Controlb 1% 2% 3% 4% 1% 2% 3% 4%

Breadloafvolume(%) 100 95 9 0 87 85 105 110 115 125

‘Bolling et al. (1973). bBread made of wheat flour without any added germ or germ oil.

negative (Chiu et al., 1968) roles played by the fat in the flour and by fat additives like phosphatides, galactolipids, and mono- and diglycerides in influencing the baking quality of wheat varieties. In order to study the changes brought about in the baking quality of wheat flour by the addition of wheat germ containing 9.1% fat, 21.8% protein, 40.0% starch, and 4.1% ash, the germ was added at 1%, 2%, 3%, and 4% levels. By the rapid mix test, Bolling et al. (1973) demonstrated that the increasing levels of wheat germ added brought about a decrease in the loaf volume, and addition of germ oil at comparable levels improved the loaf volume (Table LXVIII). They concluded, therefore, that the wheat germ oil played a positive role in improving the baking quality of wheat flour. However, the negative effect of nonfat components of wheat germ was higher than the positive effect of wheat germ oil.

C. SUMMARY

The studies of different workers have clearly shown that inclusion of raw wheat germ in the bread recipe has an adverse effect on the baking quality. Many workers have attributed this adverse effect to the germ constituent, glutathione. The effect of glutathione has been explained in two ways. Glutathione activates proteolytic enzymes, which in turn affect the gluten as well as the bread-making quality. Alternatively, glutathione weakens the gluten by reducing disulfide linkages to sulfhydryl groups. Addition of polar lipids or oxidizing agents like bromate, pre-fermentation or steeping of the germ, and a longer fermentation time brought an improvement in the quality of germ bread. Many workers have concluded that this beneficial effect is due to the oxidation of reduced glutathione (present in raw germ) to oxidized form. It has also been inferred that the improvement is due to the benzoquinone derivatives formed during fermentation. Heat treatment of the germ resulted in a similar improvement, which was attributed to the inactivation of the glutathione.


VIII. FOOD USES OF THE GERM

Until recently, wheat germ was almost wholly disposed of as an animal feed. However, after it was realized that wheat germ contains a significant quantity of proteins of superior nutritive value and vitamins, several workers investigated various aspects of its utilization as a human food. The unique characteristics of palatability and hgh nutritive value place wheat germ on a par with other foods based on animal proteins. Cirilli er al. (1971), from his analytical data on fifty different samples of germ, suggested that such a concentrated source of energy and nutrients as the germ should not go unutilized for human consumption. The addition of the germ to wheat flour would considerably improve its nutritive value. Later, during their studies on durum wheats, Cirilli et al. (1972) observed that durum semolina had a significantly lesser nutritive value, as a result of loss of the germ during milling and purification. They inferred that the nutritive value of milled products for human consumption would certainly increase if the germ could be retained during the milling operation.

The poor stability of the germ had restricted its wide usage as a human food, however. But today, various methods are available for stabilization of the germ to prevent its deterioration during storage. Some of the important uses of the germ are discussed below.

A. BAKERY AND PASTRY PRODUCTS

Among bakery products, germ bread has been studied extensively. Information on other products is scanty.

1. G e m Bread

a. Formulation. A process for the preparation of bread containing 10% of germ has been described by Hullett and Stern (1941). Commercial germ samples from soft red winter or durum wheats were found to be better than samples from hard spring varieties (Grewe and LeClerc, 1943). Bruno (1935) suggested that, when flour is to be used within a short time after milling, the germ could be retained in the flour. If the flour is to be stored for longer duration, it is desirable to add freshly extracted germ, just before using the flour to make bread. Larousse and Blanchet (1971) demonstrated that bread containing 1.5% of stabilized and lyophilized germ is better than control bread.

b. Nutritive Value, Bruno (1935) reported that bread containing the germ had better odor, flavor, digestibility, and biological value. After studying growth in rats, Cerquiglini (1938a,b) demonstrated that bread containing 2 to 5% of wheat germ was nutritionally superior to that made from the same flour without any germ. He further observed that, when fasting rats were fed, the gain in

WHEAT GERM 283

weight was 5% greater with germ bread than with the same quantity of control bread.

Feeding tests carried out by Bachmann and Leusden (1939) on bread baked from a dough containing 22% of germ showed that as much as 95% of the protein, fat, and carbohydrate of the germ was utilized by the animals. Mice receiving this bread gained in weight and showed a lower incidence of disease and a much longer life span than those receiving bread without the germ. Only a slight, negative nitrogen balance was observed in human subjects fed on a diet consisting of germ bread during a 4-day test period.

Gontzea el al. (1970) reported that bread containing wheat germ from which the fat was extracted was definitely better than bread from the same wheat flour enriched with gluten. According to them, the gain in weight, the consumption index, the protein efficiency ratio, the ratio of total nitrogen to creatine nitrogen, the amount of xanthine oxidase of the liver, and the formation of new liver proteins were significantly higher in rats fed on germ bread. Steiger (1973) has reported that wheat germ bread represents special bread enriched with important vitamins. Especially vitamins A and E and the B-group vitamins are present in wheat germ in a well-balanced form, and their beneficial effects have been demonstrated by him.

Zaitsev el al. (1974) have observed that in bread made from first grade flour enriched with 5% wheat germ the amounts of protein, lysine and essential amino acids were higher by 4, 17, and 6%, respectively, as compared to the control. In addition, the enriched bread had better taste with pronounced flavor. Use of 1.5% freeze-dried germ has been reported to bring about considerable improvement in flavor as well as yield of bread (Larouse and Blanchat, 1971).

c. Speciality Breads. Kent-Jones and Mitchell (1962) suggested that, for a bread to be labeled germ bread, it must contain at least 10% (calculated on a dry-weight basis) of processed wheat germ. Rohrlich and Bruckner (1967)

TABLE LXIX CHARACTERISTICS OF COMMERCIAL GERM BREADS"

Hovis Daren Vitbe Turog

Ingredients Germ meal (Ib) 14 14 14 14 Water (qt) 4 4 4 4 Yeast (02) 4 4.5 4.5 2

3 - - - Salt (02)

Fermentation period (hr) Nil 0.5 Nil 2.25 Process conditions

Proofing time (min) 30 - - 45

'Bennion (1967).


reported that at least 8 to 10% of germ was required to effectively improve the nutritional value of bread. The best-known types of commercially produced germ bread are Hovis, Daren, Vitbe, and Turog. These breads are prepared by using different germ meal formulations, and they contain the germ cooked with known amounts of salt, soy flour, and wheat flour. Only Turog bread is quite different. It contains smaller percentages of the germ together with caramel, which imparts a characteristic color to the bread. The ingredients for preparation of these bread are summarized in Table LXIX.

2. Biscuits and Cakes

Hertwig (1931) reported that biscuits and cakes made from self-rising flour containing toasted germ were highly acceptable and were comparable to products containing no germ. The incorporation of 12 to 15% of toasted germ in the self-rising flour was found to be optimum. The recipe proposed for self-rising flour was: patent flour, 850 gm; toasted germ, 125 to 150 gm; baking soda, 15 gm; sodium acid pyrophosphate, 16.8 gm; calcium acid phosphate, 8.1 gm; common salt, 16 to 18 gm; and dextrose, 15 gm. The keeping quality of this mix was found to be excellent, as no off-flavor developed during storage at 120" to 130°F for 25 days in a closed jar. The authors have also found that up to 15% of toasted germ could be used in biscuits without any adverse effect on its quality. Larousse and Blanchet (1971) reported an improvement in the quality of biscuits when only 0.25% of stabilized and lyophilized wheat germ was included in the biscuit recipe. According to Araki (1971), deterioration of sponge cake can be prevented by incorporation of wheat germ.

3. Pastry Products

Wheat germ has aiso been used as one of the optional ingredients for the enrichment of noodles or macaroni products (Federal Register, 1946). In addition to improving the nutritive value, the addition of wheat germ to the pastry products was reported to reduce the cost of the product.

B. SUPPLEMENT FOR CEREALS

Because of its composition, wheat germ can be used as an effective supplement for improving the nutritive value of cereals, which are known to be nutritionally inferior. The beneficial effect of supplementing with wheat germ on the nutritive value of wheat flour has been already reported. Supplementing cereals like wheat, rice, barley, and oats with 15% of defatted germ significantly improved their nutritive value by 31 to 69%, as shown by rat growth experiment (Rand

WHEAT GERM 285

and Collins, 1958). It has also been suggested that these enriched cereals can be used for the preparation of breakfast foods.

C. GERMOIL

Wheat germ is a good source of edible salad oil which is classified as a semidrying oil (Lewkowitsch, 1915). In view of the shortage and high cost of edible oils in many developing regions, the extraction of oil from wheat germ will go a long way in augmenting the supplies of edible oils. In addition to its use in the preparation of food products and vitamin concentrates, germ oil is also used in cosmetics (Jagbir Singh, 1973). Wheat germ oil has the potential for use in the preparation of margarine (Netherlands Patent Application, 1970). De- Jonge and Erkelens (1969) described a method of preparing edible oil from wheat germ by selective hydrogenation. This oil has a better keeping quality than unhydrogenated wheat germ oil. The hydrogenated oil was found to be suitable for use in bakery products.

D. FERMENTED FOODS

lwata et al. (1952, 1953) showed that wheat germ can be used in the preparation of miso and koji. Germ miso was prepared by replacing portions of rice and soybean with germ. The chemical characteristics as well as the organoleptic qualities of germ miso were similar to those of miso prepared from soybeans. Koji was prepared from wheat germ by inoculating with Aspergillus oryzae.

E. VITAMIN CONCENTRATES

Different methods have been described for separating vitamin E or vitamin B complex concentrates from the germ. The presence of high amount of vitamins in the germ, particularly vitamin E, thiamine, riboflavin, and pyridoxine, makes it a very suitable raw material for the enrichment or preparation of vitamin concentrates. The multiple uses of wheat germ suggested by Devyatnin (1944) included the preparation of (1) pyridoxine concentrate, (2) concentrate of the B-group vitamins, and (3) thiamine concentrate from the water-soluble fractions; and the preparation of (4) vitamin E concentrate, (5) sitosterol concentrate, (6) food fat, and (7) raw fat from the fat-soluble fraction.

1. Vitamin E Concentrate

The method as described by Evans et al. (1935) involved the extraction of oil with methanol and the separation of the unsaponifiable matter containing


vitamin E by using ethyl ether. Borodina (1959) has suggested a method for the purification of vitamin E. Niewiadomski et al. (1961) reported that extraction of vitamin E from germ oil with acetone containing 2%, 5%, and 10% water yielded concentrates containing 0.520%, 0.642%, and 0.7 12% of vitamin E, respectively. Increasing the ratio of acetone to oil from 1 : l to 5:l yielded a concentrate containing about 1% of tocopherols. Popova and Kirova (1964) used alcohol extraction to recover a concentrate containing vitamin E and sugars which has been used in pharmaceutical as well as in food industries.

2. Concentrates of B and E Vitamins

Several products like vitamin E-enriched oil, sterols, lecithin, B vitamins, and sugars have been prepared by McFarlane (1950) from alcohol extracts of wheat germ according to a patented process. The residue meal, after separation of the vitamins, served as a protein concentrate for food uses. The preparation, composition, and processing of polyvitamin concentrate from wheat germ has also been reported by Neumann (1952). Ciupercescu (1958) has described methods for the preparation of concentrates of vitamin E and the B vitamins by ethanol extraction of the germ.

F. ANIMAL FEEDS

The by-products of the roller flour milling industry in general form very useful and popular constituents of animal feeds. Wheat germ is mostly used as a feed for pigs, poultry, and cattle, since it is rich in protein and thiamine. Lewis and Weisberg (1952) developed a well-balanced ration for poultry using whey solids, buttermilk, and wheat germ. Iwata et al. (1955b) showed that, when compared with wheat and rice bran, wheat germ was a superior cattle feed in increasing the milk yield. The butter of these cows had a better storage life, possibly owing to the antioxidant effect of tocopherols.

Soloveichik (1946) patented a process for the preparation of a feed concentrate containing the B-group vitamins. The mixture of wheat germ, rice bran, and rice hulls was extracted with acidulated water containing alcohol and chloroform. The extract was neutralized with chalk and filtered. The filtrate was then concentrated to a syrupy consistency.

G. SUMMARY

From the studies reviewed, it is evident that utilization of wheat germ for food uses has yet to find commercial application even in technologically advanced countries. Most of the work reported has been primarily of laboratory interest. However, wheat germ, which can be recovered as a by-product of the

WHEAT GERM 287

flour milling industry, has great potential as a food supplement and can be used to enhance the nutritive value of many products. In many developing regions there is considerable scope for using wheat germ in commercially produced bakery products, mainly bread and biscuits. Preparation of vitamin E concentrate has probably had a wider application in the pharmaceutical industry. In view of its unique taste as well as make-up of nutrients like protein, amino acids, fats and vitamins, utilization of the germ in feeding the human population deserves more attention, especially in the developing countries.

IX. RESEARCH NEEDS

The foregoing account describes studies already carried out by several workers doing research on various aspects relating to the structure, separation, stabilization, chemical composition, and nutritive value of wheat germ with special reference to its effect on the baking quality of wheat flour and food uses. However, certain other aspects of these studies have yet to receive adequate attention.

1. The recovery of less than 1% germ during milling as compared to 2.5 to 3.0% present in the wheat grain, is rather low. Such a situation may be attributed to the fact that in technologically advanced countries better and cheaper sources of proteins and fat are available. This means that, even today, the major portion of the germ utilized as animal feed becomes unavailable for the population of developing regions, where protein and calorie malnutrition is widely prevalent. It has probably not been considered necessary to extend milling research on recovering the remaining 1.5 to 2.0% of highly nutritive wheat germ.

It must be recognized, however, that in developing countries, in spite of the ever-increasing need for proteins and edible oils due to the explosive rise in the population, the required technological base and facilities for improving milling efficiency are lacking. As a result, the developing regions, accounting for nearly one-third of the world’s wheat production, are unable to utilize 2.8 million tons of potentially available proteins and fat-rich material of high nutritive value for human consumption. Further research for improving the milling efficiency should logically come from the technologically advanced regions, which can more readily afford the required inputs and infrastructure in this direction.

2. No milling techniques have been developed to manufacture degermed wheat. This aspect has considerable relevance for wheat varieties that are not used for bread making. Also, a significant portion of the total world wheat produced is not milled in roller flour mills. It is milled only in small units, such as hammer mills or motor-driven mills using grinding stones. The brown flour milled therefrom at very high extraction rate (about 90% or more) is utilized in

288 S. R. SHURPALEKAR A N D P. HARIDAS RAO

traditional foods like chapatti, roti, etc., especially in India and Pakistan. Such a situation calls for urgent action in developing suitable degerming devices which can be attached as accessories to local grinding mills having small capacities of 100 kg per hour. Separation of the germ prior to grinding or during grinding will be helpful in avoiding the loss of the precious nutrients entering the bran portion of whole wheat flour, which is often sieved off before the flour is used in traditional food preparations like chapatis.

3. In spite of the exhaustive literature available on the chemical composition of the germ, very few data have been reported on the chemical composition of the germ from several varieties of wheats grown under different agroclimatic conditions. Such information is likely to be useful for separation of the germ on a commercial scale.

In the last decade or so, more and more hybrid varieties of wheat have been cultivated in many regions of the world. However, very few studies have been directed toward an understanding of the effect of hybridization on the structure, chemical composition, and nutritive value of wheat germ and its effect on baking quality. This area of research should be covered more adequately in the coming years.

4. Although the majority of the studies carried out reveal the beneficial effect of heat processing on the nutritive value of the germ, the deleterious effect of heat processing is still being demonstrated by some workers. It is therefore desirable to come to a definite conclusion on the basis of which suitable processing techniques can be decisively worked out to improve the quality of the germ.

5. Most of the processes commercially feasible for the stabilization of wheat germ are patented ones. It may be necessary to develop efficient processing techniques and suitable equipment of different capacities at moderate cost. This will be especially helpful in processing wheat germ in roller flour mills in whatever quantities it becomes available. An alternative solution would be to transport the wheat germ efficiently from individual flour mills to a central place where it could be conveniently processed for stabilization on a large scale.

6. The adverse effects of the addition of germ on the bread-making quality of wheat flour have been demonstrated clearly by several workers. However, it is interesting to note that the studies on different causes for these adverse effects do not appear t o be conclusive. Further, the remedial measures suggested for correcting these defects and improving the quality of germ bread appear to be inadequate, uneconomical, and to some extent not practicable. Thus, there is still considerable scope for working out a practical and feasible methodology to overcome these defects in germ bread,

7. Most of the work on utilization of the germ has been in the area of bread making. These studies should be extended to other food products as well as to

WHEAT GERM 289

traditional food items, which account for a significant portion of the total wheat consumption.

8. Today, triticale, the first man-made cereal, seems to be one of the promising food crops, especially in the developing regions with limited supplies of irrigation, power, fertilizers, agricultural machineries, etc. Although some work on triticale has been discussed at recent symposia (Tsen, 1974; MacIntyre and Campbell, 1974), no specific investigations have so far been reported on the structure, chemical composition, nutritive value, and separation of triticale germ. Also, its adaptability to processing and usage in food products will have to be studied in the context of different dietary patterns prevailing in various regions of the world.

REFERENCES

Albizatti, C. M. 1937. La presencia del glutatione en el germen del trigo y su influencia en

Anderson, R. J., Shriner, R. L., and Burr, G. 0. 1926. The phytosterols of wheat germ oil. J.

Andrews, J. S., and Bailey, C. H. 1932. Distribution of organic phosphorus in wheat. Ind.

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