[Advances in Food Research] Advances in Food Research Volume 1 Volume 1 || Deterioration of Processed Potatoes
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Deterioration of Processed Potatoes
BY A . FRANK ROSS1 Cornell University. Ithaca. New York
Page I . Introduction . . . . . . . . . . . . . . . . . . . 257
I1 . Common Types of Deteriorative Changes . . . . . . . . . . 259 1 . Dehydrated Potatoes . . . . . . . . . . . . . . . 259 2 . Other Products . . . . . . . . . . . . . . . . 259
259 1 . Dehydrated Potatoes: Browning . . . . . . . . . . . 259
280 . 261
266 f . Raw Material Factors Affecting Deterioration of the Dehydrated
Product in Storage . . . . . . . . . . . . . . 268 g . Packaging and Other Factors . . . . . . . . . . . 271
2 . Dehydrated Potatoes: Graying and Development of Off Flavors in Storage . . . . . . . . . . . . . . . . . . . 272
3 . Other Products . . . . . . . . . . . . . . . . 272 . . . . . 273
1 . Changes Associated with Browning . . . . . . . . . . . 273 2 . Sulfite Retention during Storage . . . . . . . . . . . 278
V . Control of Browning . . . . . . . . . . . . . . . . 279 1 . Methods of Suliiting . . . . . . . . . . . . . . . 279 2 . Attainment of Low Moisture . . . . . . . . . . . . 280 3 . Use of Potatoes Low in Reducing Sugars . . . . . . . . . 281
a . Availability . . . . . . . . . . . . . . . . 281 b . Factors Idluencing the Reducing Sugar Content of Potatoes . . 282 c . General Considerations . . . . . . . . . . . . . 283
4 . Combined Treatments . . . . . . . . . . . . . . 284 VI . Summary . . . . . . . . . . . . . . . . . . . . 285
References . . . . . . . . . . . . . . . . . . . 286 I . INTRODUCTION
111 . Factors Influencing Rate and Extent of Deterioration . . . . . . . a . Temperature and Moisture during Drying . . . . . . . 259 b . Inhibition of Browning during Processing by Suliiting . . . . d . Temperature and Moisture Content during Storage . . . . 263 e . The Effect of Suliiting on Browning in Storage . . . . . . c . Raw Material Factors in Relation to Browning during Drying
I V . Chemical Changes during Storage of Dehydrated Potatoes
About four hundred million bushels of potatoes are produced annually
Formerly Biochedt, Maine Agr . Expt . Sta . All of the authors unpublished data cited in this review are from a joint project of the Quartermaster Corps, U . 8 . Army, and the University of Maine . M . T . Hilborn, L . C . Jenness, and Emily M . Bartlett also participated in this project.
258 A. FRANK ROSS
in the United States. Of this amount, between 5 and 10% is utilized in the manufacture of potato food products. The potato industry is of com- parable importance in many other countries. The production of dehy- drated potatoes increased rapidly during the war years but this has declined to a much lower, peacetime level. On the other hand, the manu- facture of certain other products, such as potato chips and frozen French fried potatoes is rapidly increasing.
Although the production of processed potato products utilizes a com- paratively small proportion of the potato crop, it is nevertheless an im- portant stabilizing factor in the potato industry. Unless highly acceptable products are prepared and these products retain their quality until they reach the consumer, the potato processing industry will not prosper. Hence, the deterioration of potato products during and after processing is of interest not only to military authorities and to the consumer, but also to those concerned with the production, marketing and conversion of potatoes.
Because of the special requirements of the Armed Forces, emphasis dur- ing the past several years has been placed on dehydrated potatoes. A comparatively small number of published papers dealing with other types of processed potatoes indicate the existence of certain phenomena common to all. Hence, certain of the data obtained with the'dehydrated product will be applicable to other products more in demand in the civilian mar- ket.
While this review is concerned primarily with deterioration during stor- age of potato products, some attention will be given to changes during processing, or in other words, to deterioration during drying, canning, fry- ing, etc. It is becoming increasingly clear that certain deteriorative changes that occur during storage are identical in nature with undesirable changes that may occur during processing. In the first case, the changes are brought about by mild conditions over a long period of time, whereas in the second, identical changes are the result of extreme conditions for a short period. Thus the potential storage life of a given sample may be materially shortened by processing under adverse conditions.
Only those data on dehydrated potatoes obtained with a fully blanched product are reviewed here since it has been shown that blanching is essen- tial to the production of a good quality product (Cruess and Mrak, 1940, 1942a, 194213; Cruess and Joslyn, 1942; Davis et al., 1942; Beckley and Notley, 1941; Chace et al., 1941) but nothing is to be gained by a blanch longer than that required to inactivate enzymes (Cruess, Smith, and Balog, 1943; Campbell et al., 1945). Consequently, a discussion of enzymatic changes is not included.
DETERIORATION OF PROCESSED POTATOEB 259
11. COMMON TYPES OF DETERIORATIVE CHANGES
1. Dehvdrated Potatoes
One of the most important types of deterioration in storage of dried potatoes which have been properly blanched is the development of 8 reddish brown to dark brown discoloration, commonly referred to as browning. Parallel to the development of color there is formed a bitter scorchlike (caramel) taste and an equally undesirable odor. The badly discolored pieces do not reconstitute properly. In strips or dice, the color development is most intense in the center of the piece. Browning may occur also during the drying process. This so-called scorch or heat damage has been a frequent cause of trouble in dehydration plants. It now appears that heat damage and browning in storage are very similar if not identical in nature, differing chiefly in the conditions under which they occur.
Other types of deterioration have been described by workers in England. Tomkins el al. (1944) described a gray discoloration in potato strips stored at 15C. (59F.) or below, and Burton (1945b), the development of an off-flavor in low moisture potato powder stored at high temperatures.
2. Other Products
Canned potatoes have been described as having a long storage life (Rendle, 1945). However, certain deteriorative changes have been re- corded (Rogers, 1945; Rhodes and Davies, 1945). The former worker described the development of an amber-pink discoloration during heat processing and its intensification at a storage temperature of 373C. (100F.). The discolored potatoes had a burnt flavor. Rhodes and Davies described a breakdown or crumbling of canned potatoes during storage with a resultant poor texture.
Browning is also a problem in potato chip manufacture and in the prep- aration of French fried potatoes.
111. FACTORS INFLUENCING RATE AND EXTENT OF DETERIORATION
I . Dehydrated Potatoes: Browning
The early work of Mangels and Gore (1921) indicated that potatoes are rather sensitive to heat dam- age and that the extent of injury is a function of time, temperature, and humidity. More recent investigations have confirmed these results and have provided additional information on the conditions necessary to avoid this type of diacoloration. Nichols et al. (1925) recommended a finishing
a. Temperature and Mdisture during Drying.
260 A. FRANK ROW
temperature of 62.So-68.3"C. (145"-155"F.) for potatoes. In a summary of dehydration work in Canada, Davis et al. (1942) reported that one of the greatest difficulties in dehydrating potatoes is the danger of discoloration near the end of the drying period. He recommended a reduction in tem- perature to 62.8"-65.5"C. (145"-150F.) after an approximate moisture content of 10% has been reached. In their tabulated data, a greater sensitivity to heat damage of long stored potato tubers was recogniaed. A finishing temperature of 65.5"C. (150F.) was recommended for early season material and one of 62.8"C. (145F.) for that stored for a long period of time. Davis et al. pointed out that most material can be exposed to a high temperature a t the start of the operation while rapid evaporation is taking place and the temperature of the material itself is not much above that of the wet bulb, but that progressively lower dry bulb temperatures are required as drying takes place. Cruess and Friar (1943) observed dis- coloration when potatoes were dried at high humidities, held too long at 60C. (140"F.), and when they were dried at high finishing temperatures. They considered a 65.5"C. (150F.) finishing temperature as above the "scorch line" or dangerously near it. These observations establish a rela- tionship between heat reddening and moisture-temperature conditions dur- ing drying but data G Z ~ the specific effect of a given temperature as the material reaches different moisture levels are lacking.
It would appear that with a given temperature schedule during drying, browning can be minimized by a low relative humidity and a high rate of air flow. Reports are in disagreement however, on the effect of these fac- tors. Caldwell e.! al. (1945) have pointed out that if drying is too rapid, the rate of evaporation may exceed the rate of transport of water from the interior and drying out of a surface layer or case hardening occurs, result- ing in a rise of temperature in the interior of the piece.
b. Inhibition of Browning during Processing by Suljiting. Nichols and Gross (1921) compared blanching in 0.1% sodium bisulfite with other methods and in general rated the sulfited samples above the others. Cruess et at. (1944a,b) reported data showing that dipping blanched potatoes in a 0.5% bisuifite solution prevented reddening or browning during finishing at 7323C. (165F.). It was concluded that sulfiting would permit finish- ing temperatures 11.1"C. (20F.) above those in commercial use. Cald- well et at. (1945) found that sulfiting, either with SO2 gas or by dipping in sulfite solutions prior to blanching, effectively reduced or prevented heat damage. In none of the above reports were data given on the amount of sulfite retained in the dry product.
Tressler (1944) treated blanched potatoes in 0.1% bisulfite, dried at temperatures of 98.9"C. (210F.) and 85C. (185OF.) in the dehydrator and one of 623C. (145F.) in the finishing bin. The dry product contained
DETERIORATION OF PROCESSED POTATOES 261
153 p.p.m. SOa, was of good color, and was free of scorched pieces. The untreated product was of a dull color and contained scorched pieces. Friar and Van Holten (1945) found that about 300 p.p.m. SO1 prevented dis- coloration during dehydration at 73.8OC. (165OF.) whereas control samples darkened. The sulfited sample was only very slightly damaged even after two additional hours of drying at 73.8"C. (165F.) Green el al. (1946) made a study of the effect of different sulfiting practices on the color of the dried product. Since the samples were not examined until after 4% months' storage no distinction can be made between the discoloration which occurred during processing and that which occurred during storage. Samples sulfited after blanching, were of better color than those sulfited prior to blanching. Lots dipped in HSSOa and in "SO2 retained color equally well.
The reports cited above show conclusively that sulfiting is an aid in the prevention of heat damage, but most of the data are only qualitative in nature. Little consideration has been given to the variability of the raw material. The indiscriminate raising of the dehydration Wishing tem- peratures could cause trouble with some lots and might nullify the bene- ficial effect of sulfite. It should be kept in mind also that lots quite sen- sitive to heat damage deteriorate rapidly in storage and that merely preventing discoloration during drying is no assurance that the finished product will store satisfactorily.
Sulfiting destroys most of the thiamine (Morgan, 1935; Davis et al., 1942; Tressler, 1944) but decreases the loss of ascorbic acid (Davis et al., 1942; Tressler, 1944).
c. Raw Material Fact#rs in Relation to Browning during Drying. Until recently, little attention was paid to the effect of variations in raw material on sensitivity to heat damage. Davis et al. (1942) recommended a lower finishing temperature for stored potatoes than for early season ones. Black (1943) reported that potatoes stored at 1.6'4.4"C. (35'40F.) were more sensitive to heat than were new potatoes but no explanation was given. Friar (1943) encountered some lots of new potatoes of the White Rose variety that discolored seriously during dehydration while Cruess and Friar (1943) observed that potatoes which were immature or that had been stored a t low temperatures often became yellow during drying. It seems probable that at least some of the discoloration they noted was heat dam- age, yet no distinction ww made between the yellow color due to the pres- ence of carotinoid pigments in such potatoes (Caldwell et al. 1943; 1945) and that due to heat damage. Caldwell et al. (1945) reported extreme sensitivity to heat damage with physiologically immature stock, with potatoes that had been in cold storage for long periods of time, and with tubers in which dormancy was "broken" and sprouting had begun. They
262 A. FRAN'K ROSS
suggested that the great sensitivity of such tubers was due to their high content of sugars and (or) amino acids. No analytical data, however, were reported in the foregoing papers.
The behavior of potatoes from cold storage and possibly of those form- ing sprouts makes it appear likely that the presence of sugars was an im- portant factor. The possible cause of the rapid discoloration of dehy- drated potatoes from immature tubers is more obscure. The data of Appleman and Miller (1926) show that the sugar content of developing tubers decreases as maturity is approached, yet the sugar content of the most immature lots examined was about 570 total sugars on a dry weight basis and about 1% reducing sugars. Experience has shown that these levels of sugar would not cause undue sensitivity to heat damage during dehydration and storage (Campbell and Kilpatrick, 1945). On the other hand, the amount of amino nitrogen tends to increase as the tubers ap- proach maturity.
Wright et al. (1945) found a definite correlation between the color of dehydrated potatoes and the storage temperature of the raw stock. The amount of color in the dried strips of various lots increased as the tempera- ture at which the raw stock was stored approached 0C. (32F.). Those lots stored at 10C. (50F.) and 16.4"C. (60F.) were lightest in color. These differences were correlated with changes in the total sugar content of the tubers, and the discoloration during processing was attributed to caramelisation of the sugar.
Experiments with Ma...