PAU L L . P A V C E K AND T H E C O M M IT T E E ON FOOD C O M P O S IT IO N 1 F o o d a n d N u t r i t i o n B o a r d , N a t io n a l R e s e a r c h C o u n c i l , W a s h i n g t o n , D . C.
U
N DER the stimulus resulting from the increased demands by the Army and Navy for dehydrated foods, rather revolutionary advances along technical lines took place in the dehy
dration industry. Whereas during the last war dehydrated foods were unpalatable and possessed.poor storage life, many of the re
cently developed dehydrated products show promise of reaching into present civilian acceptance. Much of this superiority of the new dehydrated foods is due to recognition and application of basic principles related to varietal differences and degree of maturity in the raw product, as well as pioneering developments in washing, blanching, and drying. It was to be expected that improved techniques developed in the laboratory and the emphasis placed by the industry on fundamentals, such as inactivation of enzymes,
1 T h e m e m b e rs o f th e c o m m it t e e a re : C . A . E lv e h je m (ch a ir m a n ), P a u l L . P a v ce k ( s e c r e t a r y ), C h a r lo t t e C h a tfie ld , C . N . F r e y , A n c e l K e y s , L . A . M a y n a r d , E . M . N e ls o n , S y b il S m ith , L . B . P e t t , a n d E s th e r P h ip a rd .
prevention of rancidity, and formation of dark pigments, would result in superior products. Such superiority was reflected in the increased acceptance, which stimulated research and led to development of ultimate quality in dehydrated foods previously unassociated with them.
The growth of the dehydration industry during the last three years is indicated by the following figures: The production of white potatoes during the period 1942-43 was about 50 million pounds (dry weight); the 1944-45 production rose to 129 million pounds. Figures for the corresponding years in the case of beets are 3 million and 7 million pounds, for cabbage 7 million and 10 million pounds, onions 6 million and 21 million pounds, and sweet potatoes 8 million and 16 million pounds.
In the evaluation of dehydrated foods, the retention of nutri
tive value is an obvious criterion. Paradoxically, the literature on this phase of the subject is not very extensive. The few
pub-Ta b l e I . Vi t a m i n Da t a o n De h y d r a t e d Pr o d u c t s (i n Mi l l i g r a m s p e r 1 0 0 Gr a m s)
hydrated on a laboratory scale, and extrapolation of such data to commercially produced material is probably scientifically un
sound. Because of the paucity of data on commercial samples of dehydrated foods, the Army asked that the National Research Council, through its Committee on Food Composition, sponsor a survey to ascertain the nutritive value of the various products purchased for feeding soldiers in the foreign theaters. Natu
rally, the survey placed emphasis on products which were of great
est importance and acceptability to the soldier.
The survey was started early in 1944 and, when completed, involved almost a hundred commercial samples. The products included were: white and sweet potatoes, carrots, cabbage, beets, onions, navy bean soup, yellow pea soup, chicken noodle soup, green pea soup, tomato juice cocktail, cranberries, prunes, apri
cots, peaches, and apple nuggets. Special care was exercised to assure products directly off the production line so that storage losses could not complicate the picture. Samples were prepared from the usual 5-gallon packages in the case of vegetables and from the smaller cartons when soups and dehydrated fruits were being tested. Approximately 50-gram samples were sent to the collaborating laboratories, and large subsamples were requested to ensure a minimum of sample deviation. All results reported represent data from at least two laboratories and, where agree
ment was not good, a referee analysis was solicited.
As the survey progressed, it became evident that variations of considerable magnitude existed in the same product. For ex
ample, a tenfold variation in the ascorbic acid content and a simi
lar variation in the thiamine content of white potatoes was noted.
It was for such reason that complete operational and raw product
August, 1946 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 855 were solicited from the manu
facturer with the ultimate ob
ject in view of correlating these ranges of values with methods of blanching, time of drying, maturity, and variety of raw product and other im
portant factors. No attempt is made in this paper to corre
late these operational and raw product data with the varia
be satisfactory for these ___________________________
products. Carotene was de
termined on ether extracts
of the vegetable and reported as 0-carotene after suitable chroma
tographic separation. Saponification, either at room tempera
ture or on the water bath, was employed except in the case of sweet potatoes where the modification of Lease (5) was used.
Thiamine assay followed a thiochrome procedure (4), and was checked in some instances by the microbiological (10) and fer
mentation {11) methods.
Riboflavin determinations in all instances employed the Snell and Strong {IS) procedure. Microbiological assay {18) was also used for niacin.
Ascorbic acid was determined by the usual 2,6-dichlorophenol- indophenol method (6) ; in addition, total ascorbic acid values were obtained by the Roe. {9) dinitrophenylhydrazine method.
Since both reduced ascorbic and dehydroascorbic acids have biological activity, and since only a small proportion of the total ascorbic acid was in the dehydro form, total ascorbic acid values appear in the tables.
Table I presents vitamin data on the products tested. Re
sults are expressed on a 100-gram basis and include, in most cases, data on more than one sample of each type of product.
No identification as to source of the various samples is given in Table I although this information was obtained and was useful in correlating the variations found within the same type of prod
uct. Average values are also presented, but in many cases the wide fluctuations in vitamin values within one type of product indicate that more samples should have been tested before a valid average could be expected.
No attempt has been made in the present survey to follow' the over-all losses of vitamins during the blanching and dehydration steps. Such studies have been instigated by various commercial and experiment station laboratories {8) and should yield enlight
ening data on the extent of these losses. Extensive stability studies on commercial samples of dehydrated vegetables have been completed in the laboratories of the Continental Can Com
pany, and the first paper of this series has been published {2).
Tressler {
14
) also reported on the stability of dehydrated vegetables during storage.
It is recognized that additional losses may occur w'hen dehy
drated products are prepared for consumption. Such losses were followed on Army samples of dehydrated vegetables by Fenton (S). Preliminary reports on this work show'ed some destruction or loss of the water-soluble vitamins during preparation, but the percentage losses were not of great magnitude. In this connec
tion it should be emphasized that these more labile factors had already been lost in appreciable amounts during blanching and
Ta b l e II. Mi n e r a l a n d Pr o x i m a t e An a l y s e s o n De h y d r a t e d Fo o d s
dehydrating, and the further cooking losses are to be considered subordinate to them.
Mineral and proximate analyses on a few samples of dehy
drated products w'ere made to indicate in general w'hat values could be expected. Table II gives the results of these studies.
As in the case of the vitamin retention picture, no studies w’ere undertaken to follow the over-all losses of minerals or of the proxi
mate components. Such studies also are to be encouraged.
From the data on vitamin content it is evident that large vari
ations exist within the same product. These divergencies are understandable when the water solubility and heat lability of such factors as thiamine and ascorbic acid are considered, together with the variable practices of blanching and drying employed in the industry. Furthermore, it is well knowm that the various nu
trient contents of individual samples of freshly harvested fruits and vegetables are by no means constant (1).
The effect of sulfiting on the thiamine content of potatoes and cabbage is clear-cut. In the case of sulfited diced white potatoes, the one sample analyzed contains one sixth the thia
mine present in the average of the ten unsulfitcd products. The thiamine content of sulfited cabbage is also considerably less than that of the untreated material. This reduced amount of thiamine disappears almost completely during subsequent storage of these products (7) so that such sulfited products are practically devoid of thiamine after short periods.
The ascorbic acid content, on the other hand, is considerably enhanced, especially in cabbage where an average 100% increase is evident in the sulfited material. The presence of sulfite, if maintained during storage, also assures better retention of this factor.
Table I show's clearly that sweet potatoes and carrots are out
standing in their contribution of carotene. The former, in addi
tion, is a fair contributor of ascorbic acid.
White potatoes are superior to most of the other products tested in niacin content, and the amounts consumed by the men in certain theaters of W'ar contributed appreciably to the niacin intake. On the other hand, certain products such as onions are consumed only in limited amounts so their dietary contributions are quite meager.
Table II indicates that the chief contribution of dehydrated vegetables and fruits is to caloric intake in the form of carbo
hydrates. Some of the products, such as bean and pea soups, contain appreciable calcium and phosphorus ds compared with the other products listed. The moisture figures are not to be considered typical, although most of them fall within the 4 or 5%
Limit specified by the Army for dehydrated vegetables. Samples for these determinations, in contrast to those sent out for vitamin analysis, were not prepared immediately; therefore, some gain or loss of moisture may have taken place.
In general, it is perhaps fair to state that the major point in favor of dehydrated products is their concentrated form and adaptability to storage. The common observation is that those products showing good vitamin retention are usually those pos
sessing superior palatability and acceptance. From this stand
point alone the criterion of high vitamin content in the product is to be encouraged.
A C K N O W L E D G M E N T
In this survey the assistance of the laboratories of V. H. Cheldc- lin, Joseph H. Roe, P. B. Pearson, G. 0 . Kohler, E. M. Nelson, and C. A. Elvehjem is acknowledged in connection with the vita
min assays. A. Kramer is responsible for the mineral and proxi
mate data, and his contributions to the survey are also acknowl
edged. been destroyed er otherwise removed from a stabilized continuous phase, the droplets would all touch when the ratio of dispersed to continuous phase volume was increased to 74.02;
25.98 or, roughly, about 3:1. Inversion in an unstabilized system would then occur, with the dispersed phase becoming the continu
ous phase. Stamm and Kraemcr (9) studied the rates of break of unstable systems as influenced by various factors, and Roberts (7) investigated their inversion behavior. Hauser and Lynn (5) among others state that phase volume ratio (hereafter called phase ratio) has an important influence on the stability of emulsions generally. A recent development in breaking unstable emulsions has bceh reported by the Selas Corporation (8) whereby separation is effected through the use of a porous medium which permits the passage of only that phase which wets it.
In the investigations de agitation, variation in type and violence of agitation, upon which phase of the system under study wet the container walls first, and so on. Many of these variables could not be practically controlled in industrial scale operations. Certain qualitative observations, and also a re
covery procedure for accelerating the clarification of these emulsions, however, were unaffected by these factors. The object of this paper is to describe the latter findings.
E X P E R I M E N T A L P R O C E D U R E
Experimental work involved preparation of emulsions by various methods and observation of their qualitative behavior during break. For the systems studied (Tables I and II), a range of phase ratios from 20:1 to 1:20 was usually explored.
Agitation methods of emulsion preparation were chosen to cover A method is discussed for accelerating the break of
emulsions containing no surface active agents such as are sometimes encountered in steam distillation, solvent extraction, and other processes. The method in
volves agitating the emulsion with one to four times its volume of dispersed phase material and then allowing the system to stand idle, whereupon the originally cloudy phase clarifies rapidly. This method was effective in some systems, called totally recoverable, regardless of which of the two phases present was dispersed. In all other cases, called semirccoverable, the method was effective only when one of the two phases was dispersed. Successful clarification was usually attained with a polar but not a nonpolar dispersed phase. A totally recoverable system, therefore, usually showed that both phases present con
tained polar components, whereas a semirccoverable sys
tem contained a nonpolar and a polar phase.