[Advances in Food Research] Advances in Food Research Volume 17 Volume 17 || Tropical Fruit Technology

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  • TROPICAL FRUIT TECHNOLOGY BY N. CZYHRINCIW

    Department of Chemistry and Technology, Faculty of Agronomy, Central Uniuersity, Maracay, Venezuela

    I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11. The Significance of Fruits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

    111. Morphology and Anatomy of Fruits . . . . IV. Physical Properties of Fruits ............................................. 165 V. Some Chemical Properties of Fruits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

    ......................... 163

    A. Color, Aroma, and Flavor. ............................................ 174 B. Vitamins and Mineral Salts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 C. Carbohydrates, Proteins, Fats, and Caloric Value ....................... 182 D. Enzymes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 E. Other Substances . . ........................... 185

    . . . . . . . . . . . . . . . . . . 185 A. Preservation of Fresh Fruits and Freezing.. ............................ 185 B. Separation of the Inedible Part (Skin). ................................. 188 C. Obtaining Juices, Pulps, and Concentrates ............................. 190

    ................................... 194 E. Sweet Products. . . . . . . . . . . . . ................................... 195 F. Fermentation Products -Alcoholic and Acetic ......................... 196 G . Age of Elaborated Products ........................................... 199 H. Preservation by Irradiation ........................................... 204

    VII. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

    VI. Technical Problems ...............................

    D. Dehydrated Products . . . . . . . .

    I. INTRODUCTION

    With the expansion of the food industries at the beginning of the twentieth century, the science of food technology was established for study of the preservation of edible agricultural products in their natural state, and for the study of cheap and practical methods of processing foodstuffs, to preserve them and improve their quality.

    Processing is the series of manufacturing operations that transform the natural structure and change the proportions of the substances

    153

  • 154 N . CZYHRINCIW

    initially present in the raw materials. The science of food technology is concerned with study of the physical and chemical properties of the raw materials and the finished products, of the manufacturing processes, of the machinery used, and of the analyses used-organo- leptic, physical, chemical, and bacteriological.

    Many modern industrial processes are based on ancient experience gained in primitive manufacturing and rural handicrafts. Desrosier (1961), for example, presented a historical survey of methods of cereal preservation known for thousands of years. H.: refers to the ancient civilizations of the Middle East, of India, of the Inca Empire in Peru, etc. Such products as salted and pickled fish, cured meats, fermented drinks, bakery goods, etc., were commonly sold in the markets of the Roman Empire. Storni (1942) reports that the ab- origines of South America had developed processes to preserve certain food products, and that they could manufacture flour, sweets, beverages, and other things. Friedman (1963) states that many of our established methods of food preservation and food processing come from prehistorical times, and their safety has been tested in the crucible of human experience, not always, however, definitively and with finality.

    Studies in food technology cover various fields, characterized either by the nature of the raw materials (e.g., cereals, fruits, meats) or by the common processes of manufacturing and the resulting similarities in the finished products (e.g., bread baking, canning, bottling of soft drinks).

    As a part of food technology we study fruits, particularly the prob- lems presented by tropical fruits.

    The development of the several fields of food technology is very important in the social and economic life of all countries, as may be seen from the history of Australia, where the great boom in the past century in farming and stock raising was brought about by the develop ment of frozen-meat technology and canning industry, which made it possible for high-quality products at satisfactory prices to be exported to the markets of distant and thickly populated Europe. Peterson and Tressler (1963) consider the social and economic development of Australia to be almost an ideal case.

    The industrialization of pineapple in Hawaii is another example of the significance of food technology. The growing and processing of pineapple in Hawaii has become a principal occupation of the people of the island. New, thoroughly mechanized factories produce 57% of the worlds canned pineapple and 82% of its pineapple juice (Cushing, 1960).

  • TROPICAL FRUIT TECHNOLOGY 155

    In the United States 28% of industry is concerned with food processing, employing 13.2 90 of the national working force (Parker et al., 1952). It may be noted that during the last twenty years, the consumption of frozen foods has increased eight times, and that of baby foods 42 times (Proctor, 1960). In England, the consumption of canned juices has increased 400% in the last five years.

    The development of agriculture in distant areas would be im- possible without modern technology to preserve and process farm products. Desrosier (1961) has estimated that the present world population will have doubled in the next forty years, from three billion to six billion; the demand for foodstuffs will grow proportion- ally. Areas in the temperate zone suitable for growing wheat or rye will soon be totally occupied; meanwhile, huge areas suitable for rice and corn lie untouched in the tropics. Also, land suitable for growing the white sugar beet (Beta uulgaris) soon may not be avail- able. Although scientific research has increased the sugar content of this root from 6 to 18% within the last century, it does not seem probable that this can be carried any further. However, there is no shortage of space for growing sugar cane in the tropics.

    Equally vast possibilities exist in the tropics for the cultivation of other crops, especially for fruit plants. Thus, a great future may be expected in tropical farming, and inevitably, a parallel develop- ment in tropical food technology. This advance in tropical farming will occur sooner than the production of synthetic foods mentioned by Proctor (1960), despite the fact that the cost of many synthetic vitamins has decreased by almost half during the last six years, according to Fox (1963).

    Food technology must prepare in advance to respond to its future role as a principal factor in food production and processing. Desrosier (1961), in his absorbing book, has explained the possibilities of food production in the new tropical zones, and also its main technical difficulties. Wickiner (1960) has also discussed important aspects of farming in Asia, Africa, and Latin America.

    Food technology, particularly fruit technology, in the tropics is determined by certain specific conditions.

    (1) Natural fruit resources are potentially enormous. One recalls Humboldts calculation that the growing of 33 kg of wheat and 90 kg of potatoes requires the same ground area as the growing of 4000 kg ofbananas (Nicholls, 1901).

    There are many obscure fruit plants in the wild or semi-primitive state. The time necessary for growing plants to the first crop is rela- tively short in the tropics; this is an important factor in planning and

  • 156 N. CZYHRINCIW

    forecasting needs for raw materials. For example, papaya and passion fruit trees start to bear at the end of the first year; cashew at the third year; the mango tree between the fourth and sixth years; and the coconut from five to eight years. Another advantage is that since fruit crops ripen at different times in the tropics the manufacturing processes can work on freshly harvested fruits almost all year long.

    (2) Transport of harvests and technological processes are usually carried out at high temperatures. Van't Hoff established that every increase in temperature of 10C speeds chemical reactions two to three times. This necessitates special study on desirable or undesir- able biochemical processes, autoxidation, and, particularly, on tin- plate corrosion. Temperatures in production departments and storage houses always range between 22" and 32C. Other negative factors, such as strong sunlight and high seasonal humidity, affect the manu- facturing and storage of raw materials and elaborated products.

    (3) In the future development of tropical-fruit technology, export to far markets should be taken into account. Such factors as the conditions of manufacturing and packaging the semifinished prod- ucts, as well as the stability of the exotic products, will be of great importance.

    (4) It is probable that the products of a majority of tropical countries will be less contaminated by radioactive elements than the products of more northerly countries, as may be confirmed by comparative determinations of radioactive contamination made by Solanas et u1. (1964).

    (5) Since the larger and more experienced research institutions have been located in temperate and subtropical climatic zones, different aspects of the technology of tropical fruits have not yet been properly studied. Only botanical data and data on the principal chemical substances contained are known for tropical fruits (INCAP- ICNND, 1961; Popenoe, 1938, 1939; Landaverde, 1941; Nicholls, 1901; Chandler, 1958; Castaiieda, 1961; Pittier, 1926; Sturrock, 1959; Kennard and Winter, 1963; Aristeguieta, 1950; etc.).

    Among all tropical fruits, those most studied have been: the banana, by von Loesecke (1949) and Simmonds (1959); the pineapple, by Collins (1960); the mango, by Singh (1960); the passion fruit, by Pruthi (1963); and the coconut, by Child (1964).

    There is a serious lack of knowledge and technical data on tropical raw materials and on the most suitable methods for their processing. Some of the data and technical methods currently available, and lines for further research will be covered in the following chapters.

  • TROPICAL FRUIT TECHNOLOGY 157

    II. THE SIGNIFICANCE OF FRUITS

    Fruits are edible products, borne on the perennial higher plants, having agreeable sweet-sour and semiastringent flavors. Their water content is high, and they deteriorate easily. The texture of the mature tissues is relatively soft. Fruits develop, according to their position on the plant, in contact with the air, not with the soil.

    The edible products of the fruit-bearing higher annual plants are called vegetables, e.g., tomatoes, red peppers, cucumbers. Melons and watermelons are a sweet class of vegetables that develop on the soil surface. Nuts, which are edible products of fruit-bearing plants, have an agreeable flavor, a high content of fat and protein, a reduced water content, and a hard texture when mature. The products of fruit- bearing plants with a very high content of aromatic essences are spices (pepper, coriander with 2% oil, cardamon with 343% oil, etc.).

    The definition of fruit given by Websters International Un- abridged Dictionary states: There is no well-drawn distinction between vegetables and fruits in the popular sense; but it has been held by the courts that all those which, like potatoes, cabbage, peas, carrots, celery, lettuce, tomatoes, etc., are eaten (whether cooked or raw) with the principal part of the meal are to be regarded as vegetables; while those used only for desserts are fruits. This definition, quoted by Meyer (1960), deals more with the location of fruits within a dietetic dimension and in accord with popular experi- ence than with the technical definition of these important products.

    Hughes (1962) gives the following definition for fruits: the foods commonly designated as fruits, however, are pulpy in character, often juicy, and since they develop from the flowers of plants, they consist of the ripened seed or seeds with some edible tissues at- tached. The famous Russian scientist F. W. Zerevitinoff stated 40 years ago that fruits are poetical and vegetables are prose inspira- tions in the human nutrition.

    Rietz (1961), in his Gustametric Chart, classifies fresh fruits as a separate group of foods, placing them within the scale of taste inten- sity (which ranges from zero, for water, to 940, for red pepper) be- tween the numbers of 39 and 350. Most foods are included in this range, whole-wheat bread having a value of 12, and rum a value of 350. Thus, Rietz has confirmed one of the characteristics of fruits: fruits are foods with the widest range of flavor factors.

    Within the taste-intensity scale given above, the best-known tropi- cal fruits have classification numbers shown in Table I. In com- parison, nontropical fruits are shown in Table 11.

  • 158

    Papaya 39 Avocado 40 Cherimoya 44 Banana 48

    N. CZYHRINCIW

    Mango 75 Guava 83 Pineapple 100

    Apples 52 Grapes 72 Oranges 122

    TABLE I1 CLASSIFICATION NUMBERS OF NONTROPICAL FRUITS

    Lemon 260 Lime 350

    aCalculated from Gustametric Chart of Rietz (1961).

    Desrosier (1959) has classified foods according to their acidity, putting the fruits into two groups, one of pH 4.5-3.7, and one a highly acid group of pH 3.7-2.3.

    According to research of Ralls (1959), the specific flavor of cooked vegetables (green peas, red beets, spinach, canned asparagus) de- pends partially on acetoin and other products of its autoxidation. Acetoin is produced by glycol oxidation and is found in the fresh vegetables mentioned. It increases in content at the beginning of cooking. For instance, the content of acetoin in green peas cooked fifteen minutes may reach 340 ppm. The products of acetoin oxidation are also found in the baking of bread (75 ppm). Fresh and cooked fruits do not have such specific taste and aroma. Further studies of the above-mentioned substances would probably make possible more objective determinations of the characteristic differences between fruits and vegetables.

    Because of their organoleptic and chemical properties, fruits, with their pronounced flavors, are consumed by man in relatively smaller quantities than are the simplest vegetable products, such as rice, potatoes, and beans. Fruits are eaten in the natural or the processed state; before meals to stimulate the appetite, or to slake the thirst; or as dessert after the main course, to cleanse the palate of the flavors of soup, fish, or meat.

    Although of relatively low caloric value, fruits are an important element of human nutrition throughout the world. Ruehle and Ledin (1955) report that the mango, for instance, is probably of more

  • TROPICAL FRUIT TECHNOLOGY 159

    importance to the people of the tropics than the apple or the peach to the people in temperate countries. Fruit supplies abundant vitamins, mineral salts, and carbohydrates. The aromatic and gusta- tory substances, together with sugars, organic acids, and tannic sub- stances, intensify secretion. A relatively rich cellular structure and the pectic substances contribute to the dynamics of digestion. For the importance of fruit in the popular diet, the calculations of Jaff6 et al. (1963) may be cited, to the effect that bananas supply the people of Venezuela with 7% of their calories, 26% of their vitamin C, and 48 % of their vitamin A in the form of carotene.

    Lassabliere et al. (1950) studying the development of human nu- trition throughout the world, mentioned that fruits were consumed at an earlier date in hot climates. Bhutiani (1956), studying the importance of the development of horticulture, emphasized that in India, for instance, the population is mainly vegztarian.

    The medicinal properties of fresh and processed fruits, such as grapes, apples, and apple flour, have been studied intensely in many temperate countries, and it would seem profitable to study tropical fruits also, basing the studies on popular experience.

    Research by many workers has indicated a great variation in the chemical composition of fresh vegetable products. They reported that the chemical composition is influenced by genetics, fertilizers, degree of ripening, etc. It is enough to say, for example, that in 28 varieties of mango, the content of ascorbic acid may vary between 7 and 131 mg per 100 g Singh (1960) presented extensive data on the variation in chemical composition of different varieties of mangoes, and Cegarra (1964) presented data on some varieties of mango in Venezuela (Table 111). Riaz-ur-Rahman et al. (1956) studied 11 vari- eties of Indian guava, determining their shapes, sizes, color, and content of the principal chemical compounds. The ratio of sugar to acidity (citric acid) was found to fluctuate between 17.9 and 7.7. Rivas (1964) also determined the composition of varieties of guava (Table IV).

    All the above data demonstrate the difficulties presented to the analyst when he tries to determine the exact characteristics of fruits.

    According to research and common experience, the processing of fruit reduces its nutritive value to varying degrees, depending on the processes involved. In thermal treatment, such as cooking or sterilization, the finished product is still rich in nutritive value as compared with the raw material, but the enzymes are totally de- activated. Only with respect to enzymes do fresh fruits differ signif- icantly from processed fruits, mostly canned or bottled.

  • 160 N. CZYHRINCIW

    TABLE 111 CONTENTS OF SUGARS, ACIDS (AS CITRIC ACID), AND TANNINS OF

    11 VARIETIES OF MANGOES"

    Varieties Sugar (70) Acids (Oh) Tannins ( %)

    Martinica Glenn Irwin Selection 80 Selection 85 Kent Zill Sensation Smith Lippens Blackman

    11.68 15.15 15.24 12.26 17.00 16.37 16.11 15.95 13.65 16.58 16.75

    0.12 0.13 0.17 0.19 0.25 0.31 0.34 0.29 0.26 0.20 0.28

    0.026 0.026 0.018 0.046 0.039 0.026 0.018 0.016 0.021 0.014 0.023

    "Cegarra (1964).

    TABLE IV STUDY OF THREE INGRAFTED VARIETIES OF THE GUAVA"

    Periforme Dominica Variety de Trujillo Eloina Roj a

    Weight

    Total solids (%) Soluble solids (a) Total acidity (%)

    PH Ascorbic acid (mg/100 g) Pectins (70)

    (citric)

    60-95 g Av. 75 g

    21.52 14.0

    1.672 3.60

    0.925 214.6

    120-185 g Av. 170 g

    19.10 9.0

    0.748 4.10

    0.750 26.7

    90-150 g Av. 120 g

    17.91 13.0

    1.426 3.85

    0.800 85.8

    "Rivas (1964).

    Depending on the area of origin and principal distribution of perennial plants, fruits may be classified as being tropical, sub- tropical, temperate, or subpolar.

    Popenoe (1939) defines tropical plants in the following way: "plants which will not grow where the temperature falls much below 4.4"C are here termed strictly tropical; by tropical plants are meant (follow- ing P. H. Rolfs) those of the zone in which coconut can be grown; and by subtropical plants, those of the zone of the orange." Dassler et al. (1957) classified bananas, pineapples, avocados, etc., together

  • TROPICAL FRUIT TECHNOLOGY 161

    with citrus fruits, as southern fruits, which seems very inexact from the phytogeographic point of view.

    Among these four groups of fruit plants, the tropical group is the largest. Some 150 species are known, distributed among 40 different botanical families, and probably many more will be found. Such diversity does not exist in the temperate zones, and is far less in cold areas. However, only approximately a tenth of tropical species are cultivated on a large scale, and only this part is studied in its techni- cal aspects.

    The origin of tropical fruit plants is very diverse, as is shown in Tables VA,B (Vavilov, 1950), which also show that the majority of tropical fruit plants are from Central and South America.

    Some fruits, generally harvested in a state of pre-botanical maturity, must either be processed immediately or else stored in suitable places; such harvesting may be done to intensify, retain, or slow their maturation for a longer or shorter period. In such con- ditions, the fruits reach the required grade of commercial or industrial maturity, which may or may not coincide with the con- dition of botanical maturity. The grade of commercial or industrial maturity is that in which the fruits show that they have the most adequate physical and che mica1 properties, by organoleptic tests, for consumption in the fresh state or for industrial processing to finished products.

    A study by Krishnamurthy et al. (1960) on mango ripening may be taken as typical for demonstration of the principal dynamics of development of the physical and chemical properties for the majority of fruits (Table VI). During the ripening of fruits the content of protopectin is reduced and the content of pectin increases. Many fruits, such as bananas, the mango, and the papaya, are processed not only when they are ripe but also in the unripe state, which is not done with fruits of the temperate zones.

    Fruits are valued not only for their food value but also for their flavor and beauty. Fruits adorn the table, and fruit motifs are common in art. Fruits are symbols of feasting, both social and religious, in the poetry of many peoples. The Bible (Genesis I and 11) tells of Eden, the fruit garden of Paradise, created by God; Adam was tempted by forbidden fruit.

    Simmonds (1959) reported many references to the banana in an- cient Indian writings, and the fruit appears many times in ancient Indian art. Popenoe (1939) and Singh (1960) mentioned the role of the mango in the mythology and religious ritual of India. Alphonse de Candolle believed that the mango had been cultivated for 4000

  • 162 N. CZYHRINCIW

    TABLE V.A SOME TROPICAL FRUITS

    English name Spanish namea Botanical name Family

    Avocado Banana Bullocks heart Cashew apple Cherimoya Giant Granadilla Guava Mango Mammee apple Papaya Passion fruit Plantain Pineapple Pomerac Sapodilla Sapote Soursop Sugar apple Tamarind Yellow mombin

    Aguacate Camblir Chirimoya Merey Chirimorriiion Parcha Guayaba Mango Mamey Lechosa Parchita PIPtano Piiia Pomagis Nispero Sapote Guanibana Ri i ih Tamarind0 Job0

    Persea americana, Mill. Musu paradisiacu sapientum, L. Annona reticulata, L. Anacardium occidentale Annona cherimoya, Mill. Passijbra quadrangularis Psidium guajava, L. Mangifera indica, L. Mammea americana, L. Carica papaya, L. Passijiora edulis, L. Musa paradisiaca, L. Ananas comosus, Merr. Syzygium malaccensis, L. Achras sapota, L. Colocurpum mammosum, L. Annona muricata, L. Annona squamosa, L. Tamarindus indica, L. Spondias lutea, L.

    Laureaceae Musaceae Annonaceae Anacardiaceae An non ace ae Passifloraceae M yrtaceae Anacardiaceae Guttiferae Caricaceae Passifloraceae M usaceae Bromeliaceae M yrtaceae Sapotaceae Sapotaceae Annonaceae An nonace ae Cesalpinaceae Anacardiaceae

    West Indian cherry Semeruco Malpighia punicifolica Malpighiaceae

    The Spanish names given are those current in Venezuela.

    years. Collins (1960) reports that the pineapple was not important in the religion of pre-Columbian Mexico, but this fruit came to be the symbol of lavish hospitality in Europe, especially among the upper classes. Dassler et a,!. (1957) reported that the fine flavor of the pineapple has given it the title of the queen of all the Southern fruits. Storni (1942) quoted a saying of the Indians of South America: those who eat avocados live many years; and Merory (1960) re- ported that the same people call papayas the fruits of the angels.

    We might mention many more examples of popular interest in fruits, as compared with other foods. However, we shall cite only the following:

    Among the many spoken languages, few names of things are similar in pronunciation except for words for common and important things, such as salt, water, and wine. English speakers say fruits; Spanish speakers say frutas; Germans say friichte; Russians say frookty; and the Arabs say frote-fueke.

  • TROPICAL FRUIT TECHNOLOGY 163

    TABLE V.B SOME TROPICAL FRUITS

    Color Color Fruit 'b i le outside inside Origin"

    Avocado Banana Bullock's heart Cashew apple Cherimoya Giant Granadilla Guava Mango Mammee apple Papaya

    Passion fniit Plantain Pineapple

    Pomerac (Ohia) Sapodilla Sapote Soursop

    Sugar apple Tamarind Yellow mombin West Indian cherry

    Drupe Berry

    Nut?

    Berry Berry Drupe Drupe Berry

    Berry Berry Multiple

    fruit Berry Berry Berry Aggregate

    fruit

    Legume Drupe Drupe

    -

    -

    -

    Greenish Yellow Green Grey Green Green-yellow Yellow Yellow Brown Green to

    Yellow Yellow

    Light brown Red Brown Yellow

    Green Green Brown Yellow Pink

    green-yellow

    Yellow Yellow White Yellow or pink White Yellow Pink or yellow Yellow Ye1 lowish

    Yellow Yellow Yellow

    Yellow White Yellow Yellowish

    White White Brown Yellow Yellow

    Ab Bb A A A A A Cb -

    A A B

    A

    A A

    A A C A A

    -

    "Extracted from Vavilov (1950). 'A = Central and South American Center; B = Indian Center; C = Asia. 'Adhering by a juicy pendiculum, which is the most attractive part of the fruit.

    1 1 1 . MORPHOLOGY AND ANATOMY OF FRUITS

    A great number of different botanical families of the tropical fruit world have been investigated. As with phytoplankton or, indeed, almost any group of organisms, it has been found that, while the abso- lute numbers of a given species tend to increase poleward, the variety of species increases toward the equator. Thus, there are many more individual families and species of tropical fruits, very diverse in shape, size, and structure, classifiable as drupes, berries, aggregate fruits, etc. The digitoform contours of the banana (Fig. 1) and the rounded form of the guava (Fig. 2) are very different from the shape

  • 164 N. CZYHRINCIW

    TABLE VI

    Fruits Fruit pulps

    Water- Total Acidity Stage of Pressure Brix insoluble solids (anhyd. citric

    Variety maturity test in lbs at 20C solids (96) (9'0) pH acid) (%)

    Badami 1 25.85 8.30 9.66 17.88 2.68 3.41 2 12.66 13.30 5.98 18.90 2.85 2.08 3 6.30 18.31 0.88 19.11 3.68 0.81 4 3.90 19.32 0.22 19.37 4.04 0.38

    Raspuri 1 15.75 7.29 11.44 18.09 2.64 3.50 2 7.37 15.31 6.31 19.98 2.94 2.12 3 2.80 16.31 2.11 18.42 3.22 1.17 4 1.15 18.31 0.72 18.97 3.82 0.57

    2 20.06 12.80 5.51 18.53 3.07 1.71 3 14.25 14.31 4.11 18.70 3.11 1.69 4 2.41 17.31 1.40 18.75 4.24 0.32

    Neelam 1 30.00 12.80 5.82 17.81 3.06 1.50 2 18.44 14.31 5.02 18.30 3.10 1.28 3 10.08 16.31 3.65 18.84 3.46 0.88 4 3.47 18.31 1.30 18.90 4.74 0.16

    Tatapuri 1 - - - - - -

    Xrishnamurthy et al. (1960).

    of the pineapple, with its thorny crown. The forms of tropical fruits do not fit the geometry of classical pomology. Table V, A and B, gives an idea of the diversity of tropical fruits.

    The anatomy of fruits is interesting as an aid in identifying the origin of the pulp. Other points for study are the presence of stone cells; the micrograins of starch; the microcrystals present in some fruits, such as pineapple and pomegranate; and other elements of structure. For example, the micrograins of starch in the unripe mango are different from the micrograins of other plant products (Fig. 3).

    Lindorf (1966) studied the anatomy of different fruits, such as the sapodilla, pomegranate, and breadfruit (Figs. 4, 5, and 6). The micro- scopic structure of banana and pineapple tissues has been shown by Winton and Winton (1958). Weier and Stocking (1950) studied histo- logical changes in fruits and vegetables during processing, particu- larly by heat. However, the first studies of the anatomy of tropical fruits, specifically those of India, probably were made by Griebel (1928).

  • TROPICAL FRUIT TECHNOLOGY 165

    CHANCES IN PHYSICOCHEMICAL CHARACTERISTICS OF MANGOES DURING RIPENING AFTER PICKINGO

    Fruit Pulps

    Total p-Carotene Glucose Fructose Sucrose sugars

    Pg (%) ( %) ( %) (70) (%) Color Flavor

    345 1413 4883 6607 1231 1498 3094 4952

    513 566

    1976 130 490 844

    2381

    -

    0.22 0.70 1.91 2.07 0.25 0.84 2.13 2.06

    0.74 1.85 0.55 1.79 1.91 2.46 3.07

    -

    1.06 1.81 1.79 6.50 2.95 11.25 4.04 9.69 0.75 1.33 1.45 7.33 3.11 8.13 3.44 10.52

    2.52 4.04 4.69 2.14 3.23 9.52 2.71 1.40 2.66 3.44 2.68 4.95 7.75 4.00

    - -

    3.09 8.99

    16.11 15.80 2.33 9.62

    13.37 16.02

    7.30 8.68

    13.30 5.90 8.41

    10.09 14.82

    -

    Pale white Dull yellow Yellow Orange yellow Pale white Dull yellow Yellow Deep yellow

    Pale white Dull yellow Yellow Pale white Dull yellow Yellow Slight orange

    -

    yellow

    No flavor Mild Marked flavor Strong flavor No flavor Very mild Mild Marked

    No flavor Very mild Mild No flavor Very mild Mild Marked

    -

    IV. PHYSICAL PROPERTIES O F FRUITS

    The chief physical properties of fruits to be considered are their weight, specific gravity, specific heat, porosity, juiciness, texture, and proportion of edible parts.

    Data are seldom given on the physical properties of tropical fruits. The average weight is not always given, and, though the average measurements may be offered, these are insufficient for technical purposes. The important properties of porosity, juiciness, and texture have not yet been studied. Only in recent years has there been pub- lished, in addition to data on general composition, information on the proportion of inedible parts of tropical fruits (INCAP-ICNND, 1961).

    The specific gravity of whole fruits may determine which type of washing machinery is to be used. It may be mentioned that passion fruit has a specific gravity of much less than one.

    The porosity of food products is generally related to their elasticity in determining their texture. Elimination of gas in the intercellular

  • 166 N . CZYHRINCIW

    FIG. 1. Transverse and longitudinal sections of plantains, showing shape and size. (Czyhrinciw, 1952).

    tissue spaces is important in the processing of raw vegetable tissues. Meyer (1960) states that this gas is mainly air, with a high content of COP, water vapor, and volatile substances. Oxygen must be reduced in the tissues to prolong the life of finished products, that is, to preserve their flavor and color and to reduce corrosion in cans.

    Many fruits are processed to the liquid state. This is commonly done by pressing or mechanical disintegration. It is necessary to know the juiciness coefficient of the raw material in order to select the best method.

    The texture of the uncut whole fruit and of the edible tissue is im- portant. Skin hardness is decisive in resistance to phytopathological and entomological attack, and is important during transport. Finally,

  • TROPICAL FRUIT TECHNOLOGY 167

    the texture of the skin and the edible tissue determines the best meth- ods of cutting, peeling, etc.

    Table VII, based on experience gained during analysis and re- search (Czyhrinciw, 1955), gives data on the weight of the most im- portant fruits. Data on the proportion of the inedible part are from INCAP-ICNND (1961). Tables VIII and IX give data on specific gravity, porosity, and juiciness (Mosqueda and Czyhrinciw, 1964). Tables X and XI (Czyhrinciw et al., 1967) give data on texture. Table VII shows the average weight of some tropical fruits that belong to different botanical families. It can be seen that the largest tropical fruits weigh a thousand times as much as the smallest, reaching weights expressed in kilograms in papayas and pineapples. Temper- ate-zone fruits and subtropical fruits -for example, grapes (2-8 g), oranges (120-150 g), and apples (120-350 g), show only about one-

    Piriforme de Truli lo

    FIG. 2. Transverse and longitudinal sections of two varieties of guava (Rivas, 1964).

  • 168 N. CZYHRINCIW

    FIG. 3. Starch micrograins from unripe mango, 8 to 15 microns diameter. In polar- ized light (Chavez and Czyhrinciw, 1961).

    tenth the variation in weight. The few berries of the subpolar regions show even less variation.

    A high waste index is typical of tropical fruits. Table VII shows that it reaches 58% in avocado and 67% in passion fruit. The waste index for temperate-zone fruits, belonging to the same families, such as the Rosaceae, is generally 2-15%, reaching 50% only in the citrus fruits.

    Porosity of edible tissues varies from 5.2 %, in the mango, to 24.9%, in the Pomerac (Table VIII). It is not easy to eliminate such porosity without prolonged precooking, which greatly softens edible tissues and complicates the manufacture of tropical fruit cocktails. For com-

  • TROPICAL FRUIT TECHNOLOGY 169

    cel p

    FIG. 4. Ripe sapodilla (Achras sapote, L.) (c.) several layers of cork in skin; (ce1.p.) petrified cells; (cond. lat.) lactiferous ducts (Lindorf, 1966).

    FIG. 5. Pomegranate (Punicu granntum, L.) Petrified cells (ce1.p.) surrounded by smaller parenchyma cells (Lindorf, 1966).

  • 170 N. CZYHRINCIW

    FIG. 6. Breadfruit (Artocarpus communis, Forst.) Parenchyma with intercellular spaces (i) (Lindorf, 1966).

    TABLE VII AVERAGE WEIGHT AND PROPORTION OF INEDIBLE PART OF SOME TROPICAL FRUITS

    Weight in grams % Proportion of

    Fruit Min. MU." inedible pa&

    Avocado 500 1000 46-58 Banana 60 150 34-40 Cashew 32 80 18 Guava 30 100 4 Mammee apple 500 800 54 Mango 50 450 47 Papaya 2000 4000 25 Passion fruit 60 70 67 Pineapple 1000 4000 41 Plantain 220 450 31 Sapodilla 130 170 - Sapote 460 900 44-53" Soursop 1550 2000 41 West Indian cherry 1 5 25

    "Czyhrinciw, unpublished data. "Table of composition of aliments for South America (INCAP-ICNND).

  • TROPICAL FRUIT TECHNOLOGY 171

    TABLE VIII SPECIFIC GRAVITY AND PoRosrw OF THE EDIBLE PART OF SOME TROPICAL FRUITS

    Specific Porosity Reduction gravity in precooked in porosity

    Specific Porosity precooked fruits after precooking Fruit gravity (90) fruits ( %) ( %)

    Avocado Banana Manzana, ripe Banana Pineo, ripe Bullocks heart Guava Mango Hilacha, ripe Mango La India Papaya. ripe Papaya, unripe Passion fruit, ripe Passion fruit, unripe Pineapple, ripe Pineapple Los Andes Plantain, ripe Plantain, unripe Sapote Soursot,

    0.959 1.014 0.994 1.037 1.051 1.043 1.045 0.987 0.964 0.637 0.771 1.012 0.974 1.042 1.014 1.083 1.038

    5.4 15.7 14.5 21.2 17.0 13.2 5.2

    12.0 10.6 40.9 29.8 13.3 10.5 15.6 15.9 14.4 19.8

    1.003 1.060 1.083 1.050 1.067 1.052

    1.018 1.025

    -

    - -

    1.037

    1.109 1.077 1.085 1.070

    -

    3.2 6.7 7.8 9.5 7.3

    10.2

    2.6 2.8

    -

    - - 7.5

    7.3 7.8 6.9

    11.6

    -

    40.7 57.3 46.2 55.2 57.0 22.8

    78.3 73.6

    -

    - -

    43.6

    53.2 51.0 52.1 41.4

    -

    Mosqueda and Czyhrinciw (1964).

    TABLE IX JUICINESS OF THE EDIBLE PART OF SOME rROPICAL FRUITS

    ~~~

    Juice at Juice at

    Fruit 5 min (%) 5 min (Yo) juice ( 70) 9.6 atm for 14.2 atm for Total

    Banana Pineo, ripe

    Guava Mango Papaya Pineapple,

    ripe Pineapple,

    unripe Plantain,

    ripe Sapote Soursop Sugar apple

    4.0

    12.2 13.5 57.3 59.4

    55.6

    0.0

    29.4 38.5 42.3

    12.3

    16.2 17.1 12.9 12.2

    15.7

    3.6

    10.7 17.0 18.2

    16.3

    28.4 30.6 70.2 71.6

    71.3

    3.6

    40.1 55.5 60.5

    Mosqueda and Czyhrinciw (1964).

  • 172 N. CZYIHRINCIW

    TABLE X TEXTURE OF SOME TROPICAL FRUITS WITH SKIN

    Relatively Relatively Relatively hard semihard soft

    Scale texture Scale texture Scale texture ~~ ~

    0-5 Pineapple 11-25 Mango Hilacha, 101-300 Cashew (pendic-) ripe ulum)

    Plantain, unripe Banana Manzana

    Papaya, ripe Papaya, unripe

    Passion fruit Avocado Guava

    ripe

    5-10 Mango Hilacha, 26-100 Plantain, ripe 301+ Sapodilla unripe

    Soursop Banana Pineo, ripe

    Czyhrinciw et al. (1967). Determined by Precision Penetrometer.

    TABLE XI TEXTURE OF SOME TROPICAL FRUITS WITHOUT SKIN

    Relatively Relatively semihard soft texture texture

    A. 11-25 A. 101-300 Papaya, unripe Pineapple

    Mango Hilacha, ripe Plantain, ripe

    B. 26-100 B. 301+ Mango, unripe Banana Pineo, ripe Plantain, unripe Banana Manzana, ripe

    Papaya, ripe

    Czyhrinciw et al. (1967). Determined by Precision Penetrometer.

    parison, porosity is 25% in apples and 2% in potatoes (Smock and Neubert, 1950).

    Fruit beverages are now prepared in three ways: first, as transparent juices (apples and grapes); second, as semitransparent juices, contain- ing some homogenized tissue (oranges, grapefruit, and pineapple); and third, as nectars, in which the fruit is completely homogenized (pears, apricots, guava, mango, etc.). Transparent juices are usually

  • TROPICAL FRUIT TECHNOLOGY 173

    extracted by pressing, requiring a pressure of 5 to 25 atm to separate the liquid phase. Smock and Neubert (1950) gave the juiciness of apples as 68.2-77.3 %, and Reitersmann (1952) gave it as 55-75 96.

    At present, few tropical fruits are pressed for juice; of those men- tioned in this article, only pineapple, papaya, and cashew may be considered as juicy fruits, with about a 70% yield. The tenacious re- tention of liquid phase by the edible tissue of many tropical fruits is of great theoretical interest, for the same phenomenon is observed in pears, apricots, and strawberries of the temperate zone. Table IX, on fruit juiciness, suggests that attempts to produce nectars from other fruits would be justified, as would studies directed toward the pro- duction of other transparent bottled juices.

    From Tables X and XI, which give data on the texture of the whole fruit (with skin) and edible tissue, respectively, it is possible to class- ify fruits into three groups - relatively hard, semihard, and soft - from readings of a Precision Penetrometer expressed as 0.1 mm penetra- tion of the needle under a load of 50 g. The relatively hard group would be exemplified by apples and potatoes; the soft fruit by a ripe tomato (Table X).

    Physical properties vary not only with the maturity of the fruits but also with the type. Cegarra (1964) presented comparative data on 11 varieties of mango (Table XII).

    The specific heat of fruits must be known for calculations on refrig- eration and freezing, in addition to the heat produced by respiration. The specific heat can be calculated from theoretical formulas. Man-

    TABLE XI1 PHYSICAL PROPERTIES OF 1 1 VARIETIES OF MANGO

    Average Edible Specific Total weight Skin Seed part gravity Porosity juiciness

    Variety (td (%) (%) (%) edible (%) ( %) Martinica 475 8.39 8.62 83 1.026 13.85 20.4 Glenn 425 6.48 13.39 80.13 1.053 7.80 46 Irwin 367 8.96 9.18 81.86 1.053 7.68 48 Selection 80 328 12 19 69 1.031 12.37 30 Selection 85 269 9.48 9.23 81.29 1.053 10.53 30 Kent 500 8.20 12 79.80 1.042 8.85 30 Zill 362 9 12.56 78.44 1.064 6.38 33.4 Sensation 243 9 15.13 75.87 1.050 8.16 34 Smith 711 10.40 10.32 79.28 1.053 6.32 26 Lippens 260 10.33 12.33 77.34 1.042 8.85 43 Blackman 259 14.41 16.60 69 1.064 5.85 32

    Cegarra (1964).

  • 174 N. CZYHRINCIW

    zano (1964) determined the specific heat of the mango to be 0.889 cal; of the guava, 0.808 cal; and of the banana, 0.840 cal. These values are in very close agreement with the calculated values.

    V. SOME CHEMICAL PROPERTIES OF FRUITS

    A. COLOR, AROMA, AND FLAVOR

    Fruits show their type and maturity by their color, in the skin as well as in the edible tissues. Most skins of tropical fruits are green or yellow, rarely reddish (Table V). The edible tissue is usually yellow, sometimes white, with pinkish shades in some varieties. The green is from chlorophyll, which often disappears with maturity, leaving other pigments, such as xanthophyll and the carotenoids (Simmonds, 1959), to give the yellow color. Some fruits, such as the cherimoya and the soursop, retain the green color. Chlorophyll, when heated, darkens through the formation of pheophytin; this is another reason for the peeling of some fruits before further processing.

    Tropical fruits, which are deficient in anthocyanins, are not red or violet, except for a few like the West Indian cherry. Anthocyanins are red pigments, soluble in water, with the intensity of their color de- pending on pH. They appear mostly in the northern fruits, disappear- ing in fruits found toward the equator. Santini and Huyke (1956a) found malvin (an anthocyanin) in the West Indian cherry (Semeruco). Pruthi et al. (1961) found 1.4 mg pelargonin (belonging to the antho- cyanin group) per 100 g of tissue in the skin of certain varieties of passion fruit. The color of the pomegranate is also due to anthocyanin.

    The edible yellow tissues of tropical fruits are very rich in a large group of carotenoid pigments. Morgan (1966) found, in the carot- enoids of fresh pineapples, 50 Yo violaxanthins, 13 % luteoxanthins, 9% @-carotene, and 8% neoxanthins, in addition to smaller amounts of (-carotene, hydroxy-a-carotene, cryptoxanthins, lutein, auroxanthins, and neochromes. Pruthi (1963) reported eight forms of carotene in passion fruit, with @-carotene dominant.

    Carotenoids are fat-soluble and heat-resistant, but are easily de- stroyed by oxygen in the presence of sunlight in manufactured prod- ucts. Some carotenoids are precursors of vitamin A in the human body. INCAP-ICNND (1961) gives data on activity of vitamin A in micro- grams in the majority of the important fruits, calculated from the content of carotenoids by the use of a conversion factor (Table XIII).

  • TROPICAL FRUIT TECHNOLOGY 175

    TABLE XI11 ACTIVITY OF VITAMIN A"

    Vitamin A activity in Fruit Pd100 g

    Avocado 15-60 Banana, ripe 30-65 Banana, unripe 290 Cashew 120 Coconut 0 Guava 80 Mammee apple 30 Mango 630 Papaya 110 Pineapple 15

    Plantain, unripe 380 Soursop 5 Tamarind 20 West Indian cherry 10 Yellow mombin 70

    Plantain, ripe 165- 175

    "Extracted from INCAP-ICNND (1961).

    The color of fruit tissue changes during storage in the fresh state and during processing. These changes, which may or may not be desirable, are the work of enzyme action or other processes. These processes include autoxidation of phenols during prolonged cooking, partial caramelization, the Maillard reaction, and reactions with iron utensils or with mineral impurities in the processing water. Special studies have been made on nonenzymatic browning in fruit products (Stadt- man, 1948; Reynolds, 1963).

    Thus, it can be seen that color indicates not only the freshness and quality of the raw material but also the quality of the finished product.

    The flavor and aroma of fruits are due to many substances, volatile and nonvolatile, found in differing proportions in the skin and edible tissues of fruits. Not all these substances have been identified, either because they are present in very small amounts or because they can- not easily be isolated. The intensity of the flavor may depend partly on the variety of the fruit, on its growing conditions, and on its ma- turity. Some of these substances are specific for each species and even each variety; others are common to all fruits.

    The many specific substances which determine the flavor of some fruits are given in the following references, omitting common sub- stances such as sugars, which give sweetness; organic acids, which give acidity; and tannins, which give astringency.

  • 176 N. CZYHRINCIW

    1. Bananas

    Hultin and Proctor (1961) have found the following substances in aqueous distillate of the banana: acetic acid, methyl alcohol, ethyl alcohol, methyl acetate, ethyl acetate, 2-hexenal, 2-pentanone, and possibly isoamyl alcohol, isoamyl acetate, and 2-octanone. McCarthy et al. (1963), from chromatographic analyses of bananas, found that the bananalike flavor is due to the ainyl esters of acetic, propionic, and butyric acids. The distinctive fruity and estery tones are attributed to butyl acetate, butyl butyrate, hexyl acetate, and amyl butyrate. Wick et ul. (1966) also studied the flavor and biochemistry of volatile banana components.

    2. Pineapple

    Kirchner (1950) states that the summer pineapple has 190 mg of volatile oil per kg of tissue, and the winter pineapple has 15.6 mg/kg. The components of the volatile oil are given in Table XIV. Rodin et al. (1966) studied the sulfur-containing components of pineapple. The total volatile sulfur content of pineapple flavor concentrate was found to be 0.4-1.0% (13-32 ppb of whole pineapple). Silverstein et al. (1965), using mass spectrography and infrared and nuclear magnetic resonance spectroscopy, isolated and identified chavicol (p-allyl- phenol) and y-caprolactone from fresh pineapple.

    3. Passion fruit

    Four components, n-hexyl caproate, n-hexyl butyrate, ethyl capro- ate, and ethyl butyrate, make up 95% of the oil of passion fruit. Of these four, n-hexyl caproate accounts for 70% of the volatile passion- fruit essence (Hiu and Scheuer, 1961). The oil is present as 36 ppm of the juice.

    4. Papaya

    Katague and Kirch (1965) analyzed the volatile components of papaya chromatographically.

    It is interesting that the content of volatile oil in whole oranges and lemons is 0.3 to 0.67%, according to Braverman (1949). This indicates that efforts to extract essential oils from tropical fruits are unlikely to be practical, for these oils are small in quantity.

  • TROPICAL FRUIT TECHNOLOGY 177

    TABLE XIV COMPONENTS OF THE VOLATILE OIL OF THE PINEAPPLE"

    Summer fruit Winter fruit

    Ethyl acetate Ethyl alcohol Acetaldehyde Ethyl isovalerate Methyl n-propyl ketone E thy1 acrylate Ethyl n-caproate

    Ethyl acetate Acetaldehyde Methyl isocaproate Methyl isovalerate Methyl n-valerate Methyl caprylate Methyl ester of 5 carbon hydroxyacid Sulfur-containing compounds

    "Kirchner (1950).

    The basic sweet-acid and semiastringent flavor of fruit is due to sugars, organic acids, and tannic substances. Rapid determination of maturity for industrial purposes is done by refractometric analysis of the approximate content of sugars. Table XV gives data on the content of sugars, acids, and tannic substances (Czyhrinciw et d., 1967). Joslyn and Goldstein (1964) give data on fruit astringency.

    Fruits contain invert sugars (glucose and fructose) and saccharose. Some banana varieties have 20-50% of their sugar content as invert sugars; mango has 20-30% of its sugar as invert sugar. Sapodilla con- tains 3.7% glucose, 3.4 % fructose, and 7.02% saccharose, practically 50% invert sugar (Popenoe, 1939). Merory (1960) found 3.9% invert sugar and 7.5% saccharose in pineapple.

    Many organic acids, such as citric, tartaric, malic, and oxalic, are found in fruits, either free or as salts (e.g., oxalate crystals) and esters. Jansen et al. (1965) found that approximately 6% of the citric acid in the avocado exists as an asym-monoethyl ester. Meyer (1960) men- tioned citric and malic acid in plantains and pineapples; the avocado has traces of tartaric acid. Wolf (1958) mentioned citric and malic acids in bananas. In guava, citric acid prevails, and tartaric and levomalic acids are also present (Santini and Huyke, 1956b). Tartaric acid is dominant in the tamarind. Traces of oxalic, acetic, butyric, succinic, etc., acids are also found in fruits. Bananas, for example, contain 6.4 mg oxalic acid per 100 g pulp; Hawaiian canned pineapple contains 6.3 mg/100 g (Anon., 1949).

    Gortner (1963) reported that the malic acid content of pineapples is quite sensitive to changes in sunlight or conditions favoring water evaporation, whereas citric acid does not change in response to culti- vation factors.

  • 178 N. CZYHRINCIW

    TABLE XV CHEMICAL DATA ON CERTAIN FRUITS

    Total Acidity, sugarsb cibic Tannins

    Fruit ( %) ( %) (CLgl100 g )

    Avocado Banana Pineo Guava Mango Hilacha Papaya Passion fruit Pineapple Red cashew Sapodilla Sapote Soursop Tamarind Yellow cashew

    1.84 20.00 6.15

    11.38 6.36

    12.00 10-13

    9.12 10.96 11.69 11.52 34.50 10.89

    0.18 0.30 1.28 0.50 0.07 4.64 0.50 0.64 0.07 0.12 1.04

    11.53c 0.33

    25 17

    190 23 37 45 25

    220 57 68 76

    158 115

    Cryhrinciw et al. (1967). bAs dextrose after inversion. As tartaric acid.

    The pH of unripe banana varies from 5.02 to 5.6; in ripe banana, from 4.2 to 4.75 (von Loesecke, 1949). Garces (1967) stated that pH varies from 5.0 to 5.35 in the soursop, from 5.5 to 5.8 in the sapodilla, from 5.3 to 5.65 in the giant granadilla, and from 3.75 to 3.95 in the pineapple. Cegarra (1964) stated that pH varies from 4.5 to 5.35 in the mango, and Rivas (1964) reported a pH of 3.6 to 4.1 in the guava.

    The irregular distribution of tannic substances in cross sections of unripe and ripe plantain tissue has been demonstrated (Fig. 7).

    It is possible to characterize the flavors of fruits, to a certain degree, by a formula which involves determining the ratio acids-sugars- tannins. Riaz-ur-Rahman et al. (1956) stated that the ratio of sugar content to acid content varies from 7.7 to 17.9 in 11 varieties of guava. Smock and Neubert (1950) reported the basic flavor ratio (acids:sugars: tannins) in six varieties of apples to be 1:25:0.25.

    Mosqueda (1967) proposed classifying tropical fruits according to their basic flavors, which vary greatly. Such a classification would be of importance to fruit technology for it would permit classifying fruits, according to strength of flavor, for various uses. The first two groups, of milder flavor, would be used as table fruits. The third group would be processed, and the fourth group would be processed with some treat- ment to modify flavor, such as dilution with water or mixture with other fruits.

  • TROPICAL FRUIT TECHNOLOGY 179

    It is proposed that each fruit be classified by an arbitrary number consisting of three digits, the first of which represents acidity, calcu- lated as percent citric acid; the second, astringency, calculated as percent tannic acid; and the third, sweetness, calculated as percent dextrose. The possible range of each digit is from 1 to 9, with 9 being the maximum tolerable strength of flavor that does not fatigue the palate. By this scale, it is possible to classify fruits into four groups: simple (less than 300); moderate (300-500); accentuate (500-800); and penetrate (more than 800). According to past experience with tropical fruits, acidity is the most important criterion for the classification of flavor. Therefore, the names of the categories have been based on this quality.

    Table XVI shows a group of tropical fruits classified on this scale (Mosqueda, 1967). Included for comparison are two varieties of apples and one of pear. The acidity of the pear has been recalculated as percent of citric acid. It should be evident that this scheme of classi- fication would be useful for characterizing different varieties within a species.

    B. VITAMINS AND MINERAL SALTS

    Some mention has already been made of the importance of fruits as sources of vitamins (see p. 159) and minerals. Table XVII gives further data.

    FIG. 7. Sections of unripe and ripe plantains. Reaction of ferric chloride solution showing distribution of phenolic substances (tannins) (Czyhrinciw, 1952).

  • 180 N. CZYHRINCIW

    TABLE XVI CLASSIFICATION OF SOME TROPICAL FRUITS BY FLAVOR^

    Fruit Flavor indexb

    Avocado Papaya Sapodilla Sapote Pear

    Banana Guava Mango Hilacha Yellow cashew Red cashew Apple

    Soursop Pineapple Apple Grape

    Passion fruit Tamarind Cubarro

    Simple jlauor, 0-300 211 122 132 132 143

    314 472 312 352 482 343

    732 512 582 654

    >922 >976 >923

    Moderate jlauor, 300-500

    Accentuate ~ ~ U U O T , 500-800

    Penetrate jlauor, ouer 800

    Mosqueda (1967). bNumbers of citric acid, tannins, and total sugar content.

    Jaff6 et al. (1950) determined that Pomerac contains an average of 10 mg of vitamin C per 100 g, and sapodilla 4.5 mgllOO g. Ascorbic acid in the West Indian cherry varies from 1375 to 2259 mg/lOO g (Arostegui and Asenjo, 1954). Berries of the West Indian cherry from the state of Lara, Venezuela, average 600-800 mg/100 g (unpublished). Bukin (1963) stated that the dog-rose, with 700-4500 mg/lOO g, is the species richest in vitamin C. Bradfield and Roca Amalia (1964) found almost 3 % vitamin C in the Camu-camu (Myrcieria paraensis Berg) from Peru. Success in synthesizing this vitamin, however, will prob- ably limit interest in its natural sources.

    Vitamin C is not distributed uniformly in fruit tissues. For instance, Braverman (1963) stated that the ratio of the vitamin in the epicarp to that in the flesh and center of the guava of Israel is 9:4.

    Vitamin C, in addition to being important in the diet, is an anti- oxidant, sometimes being added to improve the flavor or color stability

  • TROPICAL FRUIT TECHNOLOGY 181

    of fruit products. Bauernfeind (1953) reported that high pH, oxygen, and heating can easily destroy this substance, which is stable in media of low pH. Proper processing conserves 80-90% of vitamin C, so that analysis of the content of this vitamin might serve as a check on proper organization of a production line.

    Vitamin B is relatively low in fruits, compared with other foods. However, the large consumption of, for instance, bananas, which may contain thiamin and riboflavin in amounts ranging upward from 0.04 mg/100 g, introduces significant amounts of these substances into the diet.

    The total content of mineral salts in fruits varies from 0.3%, in pine- apple, cashew, and mammee apple, to 1%, in coconut. According to INCAP-ICNND (1961), phosphorus in coconut is 83 mg/100 g; in avocado, 42 mg/100 g; in unripe plantain, 40 mg/100 g; in ripe plan- tain, 34 mg/100 g; in unripe banana, 35 mg/lOO g; and in mombin, 31 mg/lOO g. Calcium is abundant in mombin, with 26 mgllOO g; guava, with 22 mg/1OO g; in soursop, with 24 mg/lOO g; and in papaya, with 20 mg/1OO g. Maximum iron content is found in mombin, with 2.2 mg/ 100 g; in coconut, with 1.8 mg/lOO g; in cashew, with 1.0 mg/100 g; and in plantain and bananas, with 0.8-0.9 mgllOO g.

    Most fruits are very low in sodium (for example, 0.4-0.5 mg/100 g

    TABLE XVII VITAMIN c CONTENT OF SOME TROPICAL FRUITS~

    Fruit

    Avocado Banana Cashew Cherimoya Giant granadilla Guava Mammee apple Mango, ripe Mango, unripe Mombin Papaya Pineapple Plantain Soursop Tamarind West Indian cherry

    17 15

    219 30 20

    218 16 53

    128 28 46 61 20 26

    6 1790

    INCAP-ICNND (1961).

  • 182 N . CZYHRINCIW

    in the banana), but Wenkham et al. (1961) found that papaya has 3.6- 76 mg/100 g. Papaya can have a salty flavor. Its chloride content is related to the distance from the sea at which it is grown.

    Gardner et al. (1939) gave data on the mineral content of fruits. It is interesting that those workers found banana and pineapple almost equal to apple in contents of sulfur, calcium, magnesium, and silicon.

    c. CARBOHYDRATES, PROTEINS, FATS, AND CALORIC VALUE

    Among carbohydrates, the sugars, abundant in most fruits, get the most attention. The relation of sugars to the flavors of fruits is shown in Table XV. The starch content of fruits is of interest to technology, and tropical fruits can be divided into two groups on the basis of starch content.

    The first group is the fruits that contain starch when unripe, with starch decreasing with maturity. Such fruits are the plantains and bananas, with 15-25% starch; the mango, with 4-6%; and the tama- rind, passion fruit, and cashew, with traces. The shape of the micro- grains of starch in the unripe mango has been investigated by Chavez and Czyhrinciw (1961). Starch is found in unripe fruits of many of the Rosaceae of the temperate zone. The second group contains fruits which have no starch even when unripe, such as the pineapple, pa- paya, and guava. Starch in breadfruit (Artocarpus communis Forst) forms upon ripening.

    Cellulose, hemicellulose, and lignin form the cell walls and fibers of fruit tissue. The most fibrous of the fruits are guava (5.3% fiber) and coconut (3.8%). Other fruits range between 0.5 and 1.0% fiber. In 11 varieties of Venezuelan mango, fiber content varies between 0.41 and 0.77% (Carrillo, 1940).

    Pectic substances, found in the cell walls and juice as soluble pectin and insoluble protopectin, form gels under certain conditions (pH, sugar concentration, and cooking). The total content of pectic sub- stance varies a great deal. Elwell (1939) stated that the guava and banana are rich in pectin, whereas pineapple and pomegranate are poor in pectin. Kertesz (1951) found 0.31-0.39% pectin in natural banana pulp. Unripe plantain pulp contains 0.53-0.77% pectin; ripe pulp contains 1.0%. The mammee apple has 0.14%; the ripe rose guava, 0.46 %; and the yellow guava, 0.53 %. Garces (1967) determined the pectin content of bananas (pineo) as 0.5-0.72%; soursop, 0.36- 0.38 %; sapodilla, 0.31-0.39 %; giant granadilla, 0.37-0.44 %; and cayena pineapple, 0.01-0.06%. Bhatia et al. (1959) studied the

    possibility of extracting pectin from papaya, and Pruthi et al. (1960) studied guava pectin.

    I

  • TROPICAL FRUIT TECHNOLOGY 183

    Citrus fruits are richer in pectin. Braverman (1949) reported that the raw skin of such fruits has 1.5-3.0% pectin; the white lemon has 2.5-5.5 70.

    There is relatively little protein in fruits. The richest in protein among tropical fruits are coconuts, with 3.5% protein; avocado, with 1.5%; and plantain and bananas with 1.2%. Since most fruits have only about 0.5% protein, little work has been done on their amino acids, although Pruthi and Srivas (1964) studied free amino acids in passion-fruit juice, and Gawler (1962) studies those of pineapple juice. The chief point of interest in amino acids is their reaction with sugars, producing browning, during the preparation of concentrates.

    Little fat is found in fruits, the majority having only 0.1-0.2%. Those with the most are coconut, with 27.7%; avocado, with 10%; and mombin, with 2%. Chandler (1958) reported up to 26% in certain varieties of avocado.

    The above review indicates the essentially low caloric value of fruits, which in the majority is 30-70 ca1/100 g. Those with the highest values are, again, coconut (296 ca1/100 g), plantains and bananas (91- 132 ca1/100 g), and avocado (102-152 ca1/100 g).

    D. ENZYMES

    Enzymes are organic catalysts; that is, they promote chemical reac- tions without becoming incorporated into the substances. Since they are part protein, they are very sensitive to oxygen, humidity, tempera- ture, and changes of pH; high temperatures inactivate them. Thus, the preservation of fresh fruits or their processing may greatly affect enzyme equilibria. Enzymes are distributed irregularly in vegetable tissue (Czyhrinciw, 1951).

    The blanching or precooking process in industry is directed toward inactivating enzymes. Since peroxidase is relatively heat-stable, this process can be controlled by determination of the remaining peroxi- dase activity. According to our determinations (unpublished), the activity of the peroxidase in l-cm3 pieces of papaya is destroyed in 1 min at a water temperature of 7W-75"C. After 1 min at 60C, only 20-25% of the activity remains. At 100C, 6 minutes are needed to inactivate peroxidase in %-inch cubes of ripe pineapple. Peroxidase activity, expressed as PZ (the peroxidase index of Willstiitter) is 0.003-0.009 in ripe papaya, 0.05 in ripe pineapple tissue, and 0.084 in yellow orange skin. Sastry et al. (1961) found the PZ value, on a dry weight basis, for sugar apple (Annona squamosa) pulp to be 0.06.

    Garces (1963) gave data on the inactivation of enzymes by high temperature (Table XVIII). She further reported (1967) the following

  • 184 N. CZYHRINCIW

    TABLE XVIII INACTIVATION OF ENZYMES IN FRUIT PULP DILUTED 1:1

    Fruit

    Enzyme Mango Guava Papaya Avocado

    Ascorbic acid oxidation 75C 95C 85C - 3 min 3 min 3 min -

    Peroxidase 80C 65C 70C 85C 3 min 7.5 min 3 min 10 min

    Pectinesterase 75C 98C 90C 85C 5 min 5 min 7.5 min 7.5 min

    Phenolase 80C 85C - 85C 5 min 7.5 min - 5 min

    Garces (1963).

    data for the inactivation of pectinesterase in other fruits (pulp diluted 1:l): pineo bananas, 95C for 3 min; soursop, 85C for 3 min; and giant granadilla, 85C for 3 min. She stated that, for retention of ascorbic acid, soursop must be precooked at 80C for 5 min, giant granadilla at 90C for 5 min, and pineapple at 75C for 5 min.

    Enzyme content varies with fruit maturity. Papain, from the pa- paya, is a proteolytic enzyme found abundantly only in the unripe fruit, while very similar bromelin from the pineapple is found in the ripe fruit. Phycin has lately been recommended as being far superior to those enzymes for tenderizing meat and clarifying beverages (Whit- aker, 1957). Krishnamurty et al. (1960) studied the preparation of papain from papaya.

    Further studies on this general subject are those of Chang et al. (1965), on papaya pectinesterase inactivation by saccharose, and of Hultin et al. (1966), on the purification and properties of banana pectin methyl esterases. Rieckenhoff and Rios (1956) found pectin methyl esterase activity in guava, but very much less than in tomatoes or citrus flavedo. Reymond and Phaff (1965) studied the purification and properties of avocado polygalacturonase, and Knapp (1965) worked on avocado polyphenolases.

    Invertase in fruits may be important in alcoholic fermentation, since it differs from yeast invertase by being partially inactive during fermentation. Also, it must be inactivated by heat before invert sugar and saccharose in fruits can be determined (von Loesecke, 1949).

    Joslyn and Ponting (1951) demonstrated the importance of enzymes to fruit technology, with particular reference to color changes during storage and processing. Heid and Joslyn (1963) studied the desirable

  • TROPICAL FRUIT TECHNOLOGY 185

    and undesirable effects of enzymes in food processing. Acker (1962) studied enzyme action in foods of low moisture content, particularly dried fruits.

    E. OTHER SUBSTANCES

    Food chemistry identifies other substances in fruits that affect the flavor of the raw material and finished product. Fidler (1962) stated that many ripe fruits contain specific flavor substances; mango, for instance, can contain turpentine. Heating avocado pulp, in pre- paring sauce, causes it to form a very bitter substance, a technological problem not yet solved for that fruit. Also, the heating of papaya pulp produces a somewhat distasteful not fruity aroma, although this does not occur with the short process of heating used in preparing fruit cocktails.

    Anderson (1949) and Tatterfield and Petler (1940) investigated the distribution of a toxic alkaloid of the aporphine group in the Anno- naceae (cherimoya, soursop, etc.). With these fruits it is necessary to select raw fruits of very good quality, and to separate the skin and seeds with great care. Small (1943) reported that the content of this alkaloid in plants varies with selection and growing conditions. The cashew nut is very nutritious, containing much protein, fat, and starch. Popenoe (1939) mentioned, however, that the nuts are roasted over a charcoal fire to decompose the toxic cardol and anacardic acid of the shell, making the nut safe to eat.

    The sapodilla contains a gumlike substance which renders the passage of the cooked pulp through a finisher somewhat difficult. Research is needed on all of the above problems.

    VI. TECHNICAL PROBLEMS

    A. PRESERVATION OF FRESH FRUITS AND FREEZING

    Low temperatures (above OOC) are used to keep fruit in its natural condition for many days. Fruits are frozen only when the fruit is to be processed immediately after defrosting, because defrosted fruits lose their natural texture and begin to deteriorate. Low temperatures slow chemical and biological processes in fruits, particularly res- piration.

    Fruits damaged mechanically, phytopathologically, or entomologi- cally are subject to further deterioration. Microorganisms in general,

  • 186 N. CZYHRINCIW

    and particularly mold, easily penetrate into the edible interior tis- sues from wounds in the skin, thus stimulating decay.

    Evaporation of water content is regulated by the proper relative humidity and air temperature in the storage space. With intense evaporation, fruits wither; their natural resistance to superficial micro- organisms (fruit immunity) is lowered; the equilibrium of the enzy- matic systems is lost or shifts to an undesirable level; and the tissue elasticity is affected, which may cause distaste to the consumer of fresh fruits, or complications in technical processes, such as mechani- cal peeling.

    Fruit respiration is regulated by the temperature, within certain limits, and by the composition of the atmosphere in the storage space (increased COz, ethylene gas, etc.). Lowered temperatures, within certain limits, not only slow respiration, but help maintain the natural equilibrium of the enzymatic systems.

    Respiration is a natural process in all stored fresh vegetable prod- ucts (cereals, fruits, and vegetables). Some solid substance is lost, and heat, COz, and ethylene are produced. Under too low a temperature, the enzymatic reactions involved may go over to an abnormal state, and the fruits will begin to deteriorate. Desrosier (1959) states that the minimum preservation temperature of bananas is 13.3"C; of avocados, 7.2"C; of the mango, 10.0"C; of the papaya, 7.2"C; and of the pineapple, 7.2"C. Fidler (1962) considers that the minimum tempera- ture is 3C for English apples, and lO"-ll"C for bananas, papaya, mango, avocado, and pineapple.

    Biale (1960) presented data on the respiration of some fruits at various temperatures (Table XIX). He reported that most tropical fruits have a higher degree of respiration than fruits from other cli- mates, and he also presented data on ripening processes and on changes in certain fruit substances. Desrosier (1959) gave data on the storage temperature and humidity, preservation time, and freezing point of certain fruits (Table XX). All the conditions noted above vary somewhat with different varieties. Such conditions have been studied primarily in the preservation of bananas (von Loesecke, 1949).

    The development of the microflora of the fruit surface is controlled by proper humidity and lowered temperature of the air in the storage space. Shchez Nieva and Rodriguez (1958) determined that wild guavas may have 454 million microorganisms per pound on their surfaces. Washing the fruits reduces the microorganisms to 18 mil- lion per pound.

    Kapur et al. (1962) mentioned that mangoes of the Alphonso and Raspuri varieties, with added COz, can be stored for 35-45 days at

  • TROPICAL FRUIT TECHNOLOGY 187

    TABLE XIX RESPIRATION OF CERTAIN FRUITS IN RELATION TO TEMPERATURE"

    Respiration Fruit Temperature ("C) (ml CO,/kg/hr)

    Banana (Gros Michel) 12.5 23 15.0 38 20.0 64 25.0 79 31.0 130

    Mango (Alphonse) 2.0 7.7 4.5 10.0 9.0 18.7

    10.5 35.4 20.0 44.5 2.0 2.6

    11.0 4.2 30.0 34.0 7.5 27.0

    10.0 41.0 15.0 76.0 20.0 165.0 25.0 200.0 30.0 120.0

    "Extracted from Biale (1960).

    Pineapple (Cayenne)

    Avocado (Fuerte)

    TABLE XX STORAGE CONDITIONS FOR CERTAIN TROPICAL FRUITS"

    Storage Relative temper- humidity Storage Freezing

    Fruit ature ("C) ( %) time point ("C)

    Banana 11.7- 15.6 85-90 1-3 wk -1.0 (green) -3.3 (ripe)

    Mango 10.0 85-90 15-20 days -1.2 Pineapple, green 10.0-15.6 85-90 3-4 wk -1.65 Pineapple, ripe 4.4-7.2 85-90 2-4 wk -1.15 Papaya 7.2 85-90 15-20 days -1.05 Pomegranate -0.6-0.0 85-90 2-4 mo -2.2

    "Extracted from Desrosier (1959).

  • 188 N. CZYHRINCIW

    between 5.5 and 10C. Pruthi and Girdhari (1955) stated that the optimum conditions for passion fruit storage are temperature, 5.5- 7.2C, relative humidity, 85-90 %, and storage time, 4-5 weeks. Mathur and Srivastava (1956), Bogin and Wallace (1965), Hansen (1966), Scott and Roberts (1966), Burg and Burg (1966), and Dolendo et ul. (1966) have all studied chemical changes, respiration, ripening conditions, etc., in the storage of tropical fruits. Monvoisin (1953) indicated that the freezing point of unripe banana pulp is -O.PC, and that of ripe pulp is -3.3C.

    Mathur et ul. (1958) showed that peeled fruits, cut up or divided into sections, can be preserved for 10%-12 months with excellent results if they are kept in syrup with added ascorbic acid (0.05% by weight of syrup) at -17.8%. The fruits were kept at -28.9C for the first 48 hours. Monvoisin (1953) also reported on freezing pineapple at -15 to -18C, the fruit being cut into l-cm thick slices and put into 40-50% saccharose syrup. Many other fruits will probably be frozen someday.

    Tressler and Evers (1957) presented a study on freezing food prod- ucts, in particular fruits, dealing with the processing of bananas, pineapple, papaya, guava, avocado, and mango.

    B. SEPARATION OF THE INEDIBLE PART (SKIN)

    Removing the inedible part of the raw material is basic to food tech- nology. Since fruits differ in size and shape, peeling is difficult, and is often done by hand. In the pineapple industry, mechanization has been carried to a high point, and machines are available that can peel and core 100 pineapples a minute, each machine requiring three attendants. In less industrialized countries, however, cost and com- plexity preclude machinery, and pineapples are peeled by hand. The hands of workers require protection from the bromelin in the pine- apple, and from papain when papaya is processed (Fig. 8).

    The mango is tasty and nutritious, but preservation of this fruit re- mains at the home-canning stage because of difficulty in removing the skin and the seed. The seed is large, and the skin contains sub- stances that fatigue the palate (Sherman et al., 1958; Singh, 1960). However, the ripe mango can be peeled by freezing it at -10 to -15C until ice crystals form in the tissue; the fruits can then be peeled by a machine such as is used to peel potatoes (Fig. 9). These machines con- sist of a cylinder with an inside abrasive surface and a rotating bottom plate. The disintegrated skin is flushed away with water, and the weight loss is only 15-20%. The short and rapid freezing does not

  • TROPICAL FRUIT TECHNOLOGY 189

    FIG. 8. Peeling unripe papayas. (Courtesy Tiquire Flores Co., Venezuela.)

    cause any change in the properties of the fruit. Unripe mangoes need no freezing, for their texture is like that of the potato.

    This same method can also be used for other fruits. Good results have been obtained with sapodilla and medium-sized soursop. Loss of weight did not exceed 10-20%.

    FIG. 9. Ripe peeled mangoes after freezing (Czyhrinciw, 1967, unpublished).

  • 190 N. CZYHRINCIW

    Guavas used in fruit cocktails can be peeled chemically by placing them in baskets and immersing them for 2-3 minutes in boiling 1.5- 2.0% NaOH solution. The skin is disintegrated and separates from the fruit. The fruits are then thoroughly sprayed with water at room temperature, and any residual skin is cut off by hand. Loss of weight is 10-12%, compared with 15-22% from hand peeling.

    Mechanization of the peeling of other tropical fruits is still in the experimental stage. Some machines have been developed for paring coconuts for preparing shredded and dried coconut meat, but most countries that export such products (Ceylon, the Phillipines, etc.) rely on hand paring with a special knife. Bananas are also peeled by hand- a woman at a conveyor belt can peel 300 lb of fruit an hour.

    The problem of skin separation should be studied in relation to the aromatic, gustatory, and pectic substances present in the skins of some fruits. Ripe plantains baked in their own skins have a richer flavor, and guava paste has a better and stronger flavor when the fruits are cooked whole. Woodroof presented a complete survey of receiving and preparing fruit for processing (Joslyn and Heid, 1963).

    c. OBTAINING JUICES, PULPS, AND CONCENTRATES

    Most fruit is bottled or canned as juices or nectars; this is particu- larly true in the thirsty tropics. The production of concentrates, flours, sauces, marmalades, baby foods, wines, cordials, etc., requires the preparation of edible tissue in the form of pulp.

    Juices and nectars can be classified into three groups according to content of the structural part of edible tissue: transparent (clari- fied), semitransparent, and nontransparent (see page 172). Table XXI gives an analysis of some tropical fruit beverages made in various factories.

    The Gustametric Chart of Rietz (1961) permits comparison of the flavors of some tropical fruits and of the juices and nectars made from them. It can be seen that the majority of tropical fruit juices and nec- tars fall between 65 and 91, values that probably reflect consumer preference. Flavor intensity is less in transparent and semitransparent juices than in the raw material, and is greater in the nectars (papaya: fruit = 39, nectar = 70; guava: fruit = 83, nectar = 146). This difference may be due to the disintegrated tissue, which is all present, serving as a transporting agent of flavor substances.

    Clarification of the juice is difficult. In addition, most tropical fruits have a large content of carotenoids which are retained in the struc- tural tissue during pressing. Colloidal particles, which cause turbidity

  • TROPICAL FRUIT TECHNOLOGY 191

    TABLE XXI CHARACTERISTICS OF NATURAL FRUIT BEVERAGES

    Nectars Semitransparent (mango, papaya,

    Product juices guava, tamarind)

    Soluble solid

    Acidity as

    Average relation of soluble solid to acidity as citric acid 34.4 37.0

    substances, % 14.5-16.5 15.0-16.5

    citric acid, % 0.4-0.6 0.25-0.6

    Viscosity 3-5 10.0-40.0 Structural phase

    by 5 min centrif- ugation, YO 2.5- 15.0 15.0-40.0

    In centipoises.

    in the juice, carry flavor substances and natural antioxidant sub- stances. Therefore, fully clarified juices from these fruits will lose a substantial part of their flavor, their attractive coloring, and vitamin A content, as seen in guava and pineapple.

    Tamarind and cashew juice have strong flavors, and tamarind is highly acid, so that they must be diluted with water. This makes it possible to prepare acceptable clarified juices from these fruits. Such juices may be bottled, for they do not form a sediment displeasing to the consumer. Bottled drinks are preferred to canned ones, which may explain the popularity of artificial drinks over natural juices. Mos- queda (1966) studied the production of clarified tamarind juice, and Jain et al. (1956) and Marvaldi (1966) worked on cashew juice.

    Disintegration is held to mean the reduction of edible fruit tissue to a semiliquid slurry or pulp. Fruits of the temperate zone are usually cooked in a little water before going to the pulpers, where they are disintegrated and the skin, seeds, and a large part of the fiber re- moved. Shchez Nieva et al. (1959) reported on the use of Cowless- type disintegrators for the mango. The seed can then be separated by centrifugation (see Fig. 10). Such disintegration may be applied to other tropical fruits and vegetables, in which case, the cooking pro- cess can be omitted, with resulting conservation of the unstable flavor and aroma components. However, such a process must take into ac- count the enzymatic reactions in the fruits, particularly those of the oxydase-phenolase group.

  • 102 N. CZYHKINCIW

    FIG. 10. Mango seeds separated by centrifugation (Czyhrinciw, 1967, unpublished).

    Finishing of the pulp, before conditioning and pasteurization, is a most important process. Shnchez Nieva and Rodriguez (1958) explain the importance of removing granular particles from guava pulp. Such lignified, hard inclusions also occur in other fruits - pears, for example.

    The low pH of the majority of fruits, plus citric acid added during conditioning, permits pasteurization of the finished product, instead of sterilization.

    Tressler and Joslyn (1961) surveyed the production of juice and pulp from tropical fruits, particularly pineapple and passion fruits giving much data on juice concentration. Northcutt and Gemmill (1957) reported on the canning of banana purke, and Lawler (1967) gave information on technical progress in banana-purke canning in Honduras. Coussin and Ludin (1963) studied the manufacture of pomegranate juice and concentrate.

    Table XXII shows the organization of the production line for pre- paring juices and pulps from fruits. Factories may easily diversify their production to include sauces, creams, marmalades, etc. Passion

  • TROPICAL FRUIT TECHNOLOGY

    Beating0 Cutting

    193

    Be

    TABLE XXII FLOW CHART OF PROCESSES IN THE PREPARATION OF JUICES AND NECTARS

    Ripe Ripe Unripe pa ya mango ma

    1 Freezing

    !O

    gration

    Disinte- gration I I Centrif-

    I ugation I Centrif- ugation

    I

    Guava

    1 Pre-

    COC ing

    Soitrsop Cashew Sapodilla Tamarind apple

    I Seed

    removal b y hand

    Freezing I Freezing

    Mechan- ' 1 Mechan- ical I ical

    peeling' peeling" I

    1 Soaking

    t Finishing (pulping)

    I I

    Conditioning C

    Pasteurization

    er-

    ting

    "Mechanical peeling in the type of machines used for peeling potatoes. bTo aid in separation of seeds from edible tissue. cDilution with treated water to reduce acidity or viscosity; addition of citric acid;

    addition of sugar.

  • 194 N. CZYHRINCIW

    fruit is particularly interesting in that the high acidity of the pulp makes it a natural concentrate, which must be diluted with water in preparing the finished product (juices, wines, marmalades, etc.).

    The manufacture of guava and mango concentrates has already begun in different countries. Pruthi et al. (1963) have had success in manufacturing cashew concentrate.

    D. DEHYDRATED PRODUCTS

    High temperatures cause losses of flavor and color, particularly in pineapples and passion fruit, and darkening, particularly in ba- nanas. Attempts to produce guava flour with the L. M. Mitchell Drum Dryer failed because the product was dark in color, and the flavor of the reconstituted pulp was inferior (Luna, 1963). Flour can be manufactured perfectly well from unripe mangoes by the same equipment, such flour being suitable for cattle feeding. Table XXIII shows the composition of two samples of the finished product. The product retained its good flavor over a period of two years.

    Czyhrinciw (1952) presented a quick-cooking method for producing flour from unripe plantains; the flour contains 2.6% protein, 1.5% ash, 70.0% starch, 2.2% sugars, and 6.9% water. Flour made from unripe bananas without precooking, unfortunately, loses its agree- able flavor within a few months. Rahman (1963) presented an eco- nomical method for making flour from unripe plantains. However, the plantains should be peeled first, if the product is intended for human consumption. Cancel et al. (1962) suggested preparing ba- nanas in thin slices and frying them at temperatures from 176.7- 188.2C.

    TABLE XXIII COMPOSITION OF FLOUR MADE FROM UNRIPE MANGOES

    Sample 1 Sample 2

    Fat, 70 Proteins, % Ash, 740 Fiber, % Glucosides, % Starch, % Ascorbic acid (mg1100g) Carotene (mg/100 g)

    2.17 3.92 3.52 3.39

    87.00 40.35

    271.00 1.15

    2.63 3.45 3.13 6.10

    84.69 38.69

    528.00 2.86

    Chavez and Czyhrinciw (1961).

  • TROPICAL FRUIT TECHNOLOGY 195

    Nother et al. (1958) studied the production of pineapple-juice pow- der; Siddappa and Nanjundaswamy (1960) studied the hygroscopic properties of tropical fruit flours; and Bates (1964) studied foaming and stabilization in these flours. Other studies on dehydrated bananas, mango, guava, etc., have been made by Balasubrahmanyam et al. (1960), Jain et al. (1962), Girdhari et al. (1960), Padmini et al. (1963), and Pruthi and Girdhari (1959). Child (1964) studied desiccated coconut.

    Vacuum-drying and freeze-drying have an important role to play in preserving tropical fruits. Joslyn reported on different drying methods (Heid and Joslyn, 1963); Burke and Decareau (1964) dis- cussed problems of freeze-drying.

    The stability of flours made from tropical fruits is still a serious problem. The method of packing should be tailored to the product. In addition, the utmost care should be taken to guard any dehydrated product against insects of the genus Ephestia. This insect has a life- cycle of 9-10 weeks, and in the tropics may reproduce with explosive rapidity throughout the whole year. The larvae cause great loss in stored products by fouling them.

    E. SWEET PRODUCTS

    Good marmalades, jams, and jellies can be made from most tropical fruits. Although government regulation of sweet fruit products dates back to 1660 in France, there is still no widely accepted definition of any of these products (Rauch, 1952). Marmalades and jams are made by cooking fruit pulp with sugar (65-67%) and are nontransparent, whereas jellies are made by cooking clarified fruit juice with sugar, and are transparent or semitransparent. All have a liellylike tex- ture, which comes from the formation of gels when a solution of pectin is heated and pectin polymolecules are formed, bonded together by sugar and acids.

    Citric or apple pectin must be added when they are prepared from pulps diluted with water. Rieckehoff and Rodriguez (1960) studied the addition of pectin in making guava products. Pectin need not be added to guava pulp with a final sugar content of 70-75%, but is needed with a sugar content of 65-67%.

    Industrial experience has shown that, to manufacture 1 kg of mar- malade from pineapple, guava, mammee apple, or passion fruit, it is necessary to use 0.7-0.75 kg pulp, 0.55 kg sugar, and 10-15 g pectin (citric or apple at 100-150 index).

    Elwell (1939) presented comparative data on the manufacture of

  • 106 N. CZYHRINCIW

    jellied products. For example, when the temperature reaches 105C in apple pulp, the desired concentration of 65 940 sugar, and the poten- tial for gel formation, have been reached. Comparable temperatures are 106.lo-107.2"C for grape jellies and 107.8"C for guava jelly. Guava needs more sugar than does apple, since it is poorer in pectin. Marmalades made only from quinces or apples are not likely to need extra pectin.

    Consumer preference in tropical countries dictates a lower acidity in marmalades and jellies made there (0.3-0.6%) than in the temper- ate zone. Thus, there is between 110 and 225 times as much sugar as there is acid, in contrast to the usual 75 to 90 times of the northern countries. The low content of natural pectin and acidity requires the addition of pectin from other sources.

    Gomez (1963), in studying the quality of marmalades, found it to be necessary to control water dilution of the pulp; less dilution gives a more natural taste. He recommends ash determinations and alcohol precipitations in quality control of the finished product. For a better product, Luh et al. (1964) recommend raw material of good quality and use of the vacuum cooker.

    Manufacture of candied fruits has recently increased greatIy (Fig. 11). Unripe papaya and pineapple are promising raw materials. Fruits need no prior treatment with sulfurous acid if they are to be used immediately, but diced fruit for export must be treated for tempo- rary preservation (Fig. 12). Chakraborty et al. (1962) studied the cashew apple in candy making.

    Methods are also being developed for canning fruits in syrup. Guava, mango, and, especially, unripe papaya are excellent for can- ning (Figs. 13, 14). Fruit cocktails, especially a mixture of pineapple and papaya with a little guava, have been manufactured and have found ready consumer acceptance.

    F. FERMENTATION PRODUCTS - ALCOHOLIC AND ACETIC

    In the more northerly regions, alcoholic fermentation is usually applied to the production of beverages from grape juice or from cereals. In the tropics, rum is produced from sugar-cane molasses. In recent years wine has been produced from imported grape-juice concentrates, which, without going into detail, is regarded as a pseudo- industrial process since it deals with partially processed, denatural- ized, raw materials.

    There are great possibilities for making wines in the tropics from local fruits. Sinchez Nieva (1951) draws attention to pineapple and

  • TROPICAL FRUIT TECHNO1,OGY 197

    FIG. 11. Venezuela.)

    Manufacturing candied fruits froin unripe papayas. (Courtesy Selecta Co.,

    tamarind wines; Dyal Singh (1956) refers to fruit wines in India; Czyhrinciw (1966) studied the making of wines from passion fruit and mango. Amerine and Cruess (1960) reported on the technology of wines made from pineapples, pomegranates, etc. As for countries in the temperate zone, Canada, in 1958, used more than 700 tons of loganberries and blackberries for winemaking. Wines made from apples and other fruits are well known in Europe. The Ukraine for- merly had two research centers concerned with winemaking: one at Odessa, for grape wines, and one at Uman, for wines made from ap- ples, strawberries, raspberries, etc.

    Making wine from fruits other than grapes differs from the tradi- tional process mainly in the initial stage, preparation of the must for fermentation. This usually requires peeling and mechanical disinte- gration of the fruit. Also, must from fruits other than grapes is more

  • 198 N . CZYHRINCIW

    FIG. 12. Preparation of pineapples to be preserved in sulfurous acid (for export). (Courtesy Infrut Co., Venezuela.)

    often conditioned by the addition of water, sugar, and citric or tannic acids. Conditioning may involve diluting the pulp, making up for a lack of natural sugar, or controlling the acidity or astringency of the final product. Sugar is usually added in two or three batches during the first few days of fermentation.

    Further study is warranted on the practicability of manufacturing wines, semidry and sweet, in a range of colors and having the specific flavors of fruits such as passion fruit and cashew apple. Various alco- holic fermentations, made with substantial amounts of added cane sugar, appear to indicate that many tropical fruits contain invertase (saccharase) of sufficient potential. The invertase content of the fruit, even though this enzyme is also present in the yeast, must be studied

  • TROPICAL FRUIT TECHNOLOGY 199

    in relation to the addition of sugar. Satisfactory fermentation curves have been demonstrated in mango and passion-fruit musts; in both cases, Fleischmanns active dry yeast was used (Fig. 15).

    Muller et al. (1964) investigated, by gas chromatography, numerous volatile substances in dry passion-fruit wine. Griinwald (1967) also investigated the fermentation dynamics of passion-fruit wine, and concluded that the flavor and aroma substances appear in like propor- tion in the raw material and the finished product. The esters, in par- ticular, were determined by gas chromatography. Tables XXIV and XXV give data on passion fruit and mango wines.

    Production of vinegar from tropical fruits would be of interest in some countries. Arispe (1967) has prepared vinegar from several, giving analyses and technical data. The production of vinegar from pineapple waste has special interest (see Table XXVI).

    G . AGE OF ELABORATED PRODUCTS

    Organoleptic criteria for determining the age of food products have been known for a long time, as witnessed by the Italian who said: Todays bread; last years wine. It is true that fresh bread and cake are tastier, and probably more nourishing than when they are several days old. Staleness results from evaporation of water, the regrouping

    FIG. 13. Cooking of fruits in syrup. (Courtesy of Tiquire Flores Co., Venezuela.)

  • 200 N. CZYHRINCIW

    FIG. 14. Fruits in syrup (sterilized). (Courtesy of Tiquire Flores Co., Venezuela.)

    of certain chemical components, autoxidation, etc. On the other hand, liquors and wines become smoother and mellower when their chemical reactions have some time to proceed. Unfortunately, the majority of products made from tropical fruits do not improve with age.

    Ascorbic acid (vitamin C), being an active reducing agent, can serve as an index of the stability of products elaborated from raw material containing this substance. Stadman (1948) and others have regarded this substance as a natural indicator of autoxidation; the age of cer- tain products might be correlated with the loss of ascorbic acid. Czyhrinciw (1954) studied the dynamics of vitamin C and the organo-

  • TROPICAL FRUIT TECHNOLOGY 20 1

    15

    - 14 5 13.- 0

    leptic properties of papaya nectars stored 8 months at 29.4 and 32.2C finding the average loss of vitamin C to be 17.2%. He stated that the tentative storage life under tropical conditions is proposed as being 2 years for papaya nectar and 1.5 years for bananas in heavy syrup. Braverman ( 1963) mentioned that extensive changes in products of fruits, especially in color and flavor, run parallel to losses of ascorbic acid during storage.

    Most manufactured products are at their best when young, but a few days (a few hours for bread) are needed to stabilize the struc- ture and reach uniformity. More study is needed on determining the age of food products, especially in tropical countries, where storage is difficult. Hearne (1964) discussed problems of storage, and Parpia (1956) reviewed food storage in India.

    The development of metal containers with protective linings of tin and enamel, of glass containers, and, lately, of plastic and of aluminum containers, is of great interest to food technology, for corro- sion during storage is a serious problem. Internal corrosion of cans,

    ..

    Days

    FIG. 15. Rate of alcohol production during fermentation of passion fruit and mango wines. Passion fruit win-; mango wine------- (Czyhrinciw, 1966),

  • 202 N. CZYHRINCIW

    TABLE XXIV SENSORY ANALYSIS OF THE WINES FROM PASSION FRUIT AND MANGO

    Wine Passion fruit Mango

    Color Typical white wine Typical white wine (slightly yellow)

    Flavor Pleasant, vinous Pleasant, vinous special fruity touch

    Body Good Good Other indices Without defects Without defects Type of wine Sweet dessert wine Fine white table wine

    Czyhrinciw (1966).

    going on a long time, may produce enough hydrogen gas to swell the cans. In humid places, external corrosion makes the cans un- sightly. Britton (1952) reviewed the main criteria of tinplate quality: the thickness and porosity of the tin layer. For the tropics, we believe that 1.5 tinplate is to be preferred to 1.25. Cruess (1948) gave informa- tion on the rate of increase with age of the tin content of canned vegetables.

    Jakobson and Mathiesen (1946) consider that the mean storing capacity of the products is more than doubled when the storing tem- perature is decreased by 10C. The temperature coefficient is about the same for lacquered cans as for unlacquered ones (aluminum). Various investigators, including Felin (1952), also dealt with low- temperature storage of preserved products.

    Acidity or the concentration of the product is not always strictly correlated with corrosion. Especially active substances are the antho- cyanins -certain amino acids, tannic substances, oxalic acid, etc. Numerous observations of the corrosive activity of various products show that because of their different origins or because of different processing methods they are not really comparable, although de- signed to be so.

    Corrosion can often alter the color or flavor of a product. Some ac- quire a metallic taste, which indicates how high the content of tin and/or iron is. Czyhrinciw (1954), working on the corrosion of tin- plate, ranked fruit products in increasing order of corrosive ability as follows: tropical fruit cocktail, passion-fruit juice, tamarind juice, pineapple juice, papaya juice. Concentrated papaya pulp was the most corrosive. The products were stored 12-20 months at 25-35C.

    Boyle et al. (1957) recommended enameled cans (citrus or T enamel) for guava nectar. Sherman et al. (1958) state that mango may

  • TROPICAL FRUIT TECHNOLOGY 203

    TABLE XXV PHYSICAL AND CHEMICAL MEASUREMENTS OF PASSION FRUIT AND MANGO WINES

    Passion Fruit Mango Maracuya Hilacha

    Wine (Age 8 mo) (Age 15 mo)

    Density Number of wines Alcohol at 15C, % Brix scaleb Total acid as citric, Yo PH Volatile acid, % Tannic substances, % Esters as ethyl

    acetate, % Aldehydes as

    acetaldehyde, % Furfural, % Higher alcohols, %

    1.0200 3 12.53 14.5 0.81 3.26 0.018 0.023

    0.038

    0.0035 0.0004 0.072

    1.0002 3 13.68 5.0 0.79 3.20 0.027 0.008

    0.040

    0.0050 0.0001 0.027

    Czyhrinciw (1966). *Determination after distilling off two-thirds of the volume and diluting to original

    volume with distilled water.

    TABLE XXVI PROPERTIES OF VINEGAR FROM SOME TROPICAL FRUITS

    Vinegar from Vinegar from Properties pineapple waste passion fruit

    Specific gravity (at 15C) 1.014

    Total acidity (acetic acid), g/100 cc 5.18

    Nonvolatile acidity (citric acid), g/l00 cc 0.35

    Volatile acidity, g/l00 cc 4.83 Alcohol, % 0.30

    1.011

    5.1

    2.0 3.1 0.2

    Reducing sugars

    Soluble solids, % 4.00 3.0 Esters, mg/100 cc 6.30 6.0

    Tannins, mg/100 cc 35.00 32.0 Oxidation number 178.00 320.00

    (invert sugars), 7% 0.15 -

    Aldehydes, mg/100 cc) 20.60 12.0

    Arispe (1967).

  • 204 N. CZYHRINCIW

    be canned with syrup in tin cans. Rodriguez (1962) suggested packing guava paste in cardboard boxes.

    H. PRESERVATION BY IRRADIATION

    Irradiation, the newest method of food preservation, is still in an early stage of development. Romani (1966), Maxie and Abdel -Kader (1966), and Sommer and Fortlage (1966) discussed theoretical prob- lems and experimental results of this method. Fergason et al. (1966) studied the effects of y-radiation on bananas. Dharkar et al. (1966a,b) studied irradiation of mangoes, developing a heat-irradiation process for sterilizing mango and sapodilla slices in cans. These methods look promising.

    VII. CONCLUSION

    During the last ten years a great development in tropical fruit technology has been carried out in research centers in California, Hawaii, Florida, Puerto Rico, Brazil, Venezuela, India (at Mysore), the Philippines, and other places. Much, however, remains to be done.

    There are certain characteristics of tropical fruits which can be correlated with latitude. For example, the anthocyanins in fruits de- crease toward the equator. In addition, the number of botanical fami- lies, the diversity of fruit form, sensitivity to temperature, and rapid growth to the first fruit-bearing, all increase in fruits of lower latitudes. Tropical fruits have increased carotenoid content and a higher per- centage of inedible part. The potential resources of tropical fruits are enormous.

    The great diversity in flavor and chemical composition of tropical fruits gives many possibilities for industrial enterprise, although it must be remembered that the parallel diversity in form and size will greatly complicate the technology.

    The giant granadilla has a flavor resembling that of pears. The pas- sion fruit and the pineapple can be developed further. The papaya has little astringency, while the cashew and the yellow mombin are very astringent. Acid fruits, such as the lemon and the vinagrillo (Averrhou blimbi, Oxalidaceae) should be given attention. The high sugar content of ripe plantain (up to 21.1 %) and of the mango (up to 25%) merit their study as food products. The exotic flavors of these fruits are almost totally unknown in the north, and food products based upon them should find a ready market. In addition, the vitamin

  • TROPICAL FRUIT TECHNOLOGY 205

    C and carotenoid content would be a point of interest to the public. The shortage of anthocyanins, which give the pleasing red color to fruits, suggests that such fruits as Piritu or Cubarro (genus Bactris, Palmaceae) should be cultivated.

    Excellent beverages may be made from mango, passion fruit, giant granadilla, cashew, tamarind, and soursop. Cupana (Paullinia cupana, Sapindacea) can be cultivated for beverages; Guarana types have been successful in Brazil. Schery (1956) mentions the high content of caffein and tannins in this fruit. Miller et al. (1957) submitted formulae for combined nectars of banana-guava, papaya-banana, and papaya-pineapple.

    Fruit sauces and condiments may be made from mango, tamarind, etc., to compete with tomato catsup. Guava and papaya catsup formu- lae have been submitted by Miller et al. (1957). Pruthi and Bedekar (1963) and Bedekar and Pruthi (1963) studied the salting of raw mango slices for pickling and for chutney, an Indian product popular the world over.

    The potential is great for producing marmalades, jams, and jellies; fruits in syrup; and particularly fruit cocktails. The exotic flavors of mango and other fruits should be appreciated in the north. Pomerac (Fig. 16) is a promising fruit.

    Wines and cordials can be made from many tropical fruits (mango, cashew, passion fruit, etc.) Passion fruit makes a good cordial, and an excellent red cordial can be made from Piritu or Cubarro. Wiistenfeld

    FIG. 16. Pomerac (Ohia).

  • 206 N. CZYHRINCIW

    (1953) reported on pineapple and banana liqueurs, and Reitersmann (1952) on banana liqueurs. Vinegar production has already been men- tioned.

    Pulp concentrates, sliced semiproducts, and fruit flours may become important. Ross (1960), Seale and Sherman (1960), Sherman et aZ. (1958), Boyle et a2. (1957), Cruess (1961), Miller et a2. (1957), Kanhiro and Sherman (1956), and La1 (1956) have given formulae for many different products. Baby foods are also becoming important.

    The science of food technology should coordinate studies on the following:

    1. Wild farming, and semiwild botanical species of industrial value. At the beginning, efforts should be made to eliminate the differences of opinion between growers and industrialists. Adam (1962) stated that the processor is primarily interested in the quali- ties of color, flavor, and texture, whereas the grower is more con- cerned with yield, disease resistance, and ease of cultivation and harvesting; yet, the processor can no more ignore the growers re- quirements than the grower can affect indifference to the ultimate use of his crops.

    2. Influence of chemical composition on the technical aspect. The study of pectic substances, astringents (tannins), enzymatic sys- tems, complete identification of sugars and acids, and the identifi- cation of gustatory and aromatic substances should be studied, in addi- tion to the ordinary analyses of carbohydrates, proteins, fats, vitamins, mineral salts, and moisture.

    3. Physical properties. Weight, specific gravity, porosity, juici- ness, texture, freezing point, specific heat, etc., deserve study.

    4. Bacteriological aspects. 5. Preservation in the fresh state at reduced temperatures and

    freezing. Temperatures, humidities, and storage times must be estab- lished for the various products.

    6. Irradiation. 7. Mechanization of processes. 8. Retention of natural color and flavor in manufacturing pro-

    9. Corrosive properties of tropical products. 10. Age of finished products, packing, and storage; temperature-

    11. Radioactive contamination. 12. Extension of available assortments. 13. Utilization of industrial wastes. 14. Historical aspects.

    cesses.

    humidity.

  • TROPICAL FRUIT TECHNOLOGY 207

    15. International trade and export. It should be noted that few tropical fruits or fruit products are known outside their own areas. The Fruit World Map (1963) of the international fruit and vegetable trade, for example, shows only the important banana and pineapple centers. Other fruits are not even mentioned.

    16. Quality standards for the raw material and finished products. 17. Production planning and cost accounting. 18. Bibliography. 19. Technical publicity. 20. Technical education.

    Work on any of the factors listed above would contribute enor- mously to the development of tropical fruit-producing countries. This applies with equal force to tropical vegetables.

    ACKNOWLEDGMENTS

    I express my thanks to the following professors of the Faculty of Sciences of the Central University of Venezuela for their help and advice: Dr. Leandro Aristeguieta, Professor of Botany; and Dr. W. G. Jaffk, Professor of Biochemistry. I am also indebted to Dr. C. 0. Chichester, Department of Food Science and Technology, University of California, Davis, California, for his suggestions in preparing this text.

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