Effect of Cooking on Solubi Cottonseed-Meal Proteins
J
H. S. OLCOTTl AND T. D. FONTAINEZ Mellon Institute, Pittsburgh, Penna.
The industrial process of cooking cottonseed has been handled as an art, with determinations of proper temperature and time of cooking made by feel. As a result, commercial meals of widely differing characteristics are being produced. A study of the solubility in 3 per cent salt solution and in water of the proteins of commercial cottonseed meals indicated that they had been subjected to different cooking conditions. Growth experiments with rats suggested that those meals which had been heated more were less effective
sources of protein. The effects of autoclaving at different temperatures on the solubility of the cottonseed-meal proteins are used as a basis for the suggestion that, for optimal feed characteristics, cottonseed should be cooked at lower temperatures and for longer periods rather than at elevated temperatures for shorter times. A laboratory assay of commercial meals, based upon the solubility of the proteins, is proposed for use in mill laboratories as a method of controlling cooking procedure.
N THE commercial production of cottonseed oil, the cottonseed are decorticated, rolled, and cooked prior t o the pressing operation. According to Thornton ( 6 ) , “the function of cooking is t o permit the proper adjustment of moisture, rupture the oil-bearing cells, coagulate the proteins, coalesce the gummy materials, destroy molds and other lower organisms, and make the cake more palatable and more wholesome by inactivating the gossypol.” By experience, oil-mill superintendent,s have arrived a t procedures which give the highest yields of oil with minimum refining losses. Less attention has been paid t o the properties of the cottonseed-meal residue. As part of a program of study on cottonseed and its products ( I ) , it was found that the nutritive value of the proteins in commercial cottonseed meals varied with different samples. Inasmuch as it had been shown that autoclaving reduced the nutritive efficiency of the proteins of ether-extracted cottonseed (4),it appeared possible that some part of the variations in commercial meals might be attributable to differences in the amount and character of the cooking to which the proteins had been subjected. A method for estimating quantitatively the denaturation of the proteins so incurred was suggested by the results of previous studies ( 8 , 3 )in which water and salt solutions had been used to extract cottonseed protein fractions. I n this method the water-soluble nitrogenous compounds are assumed t o represent the native albumin plus the less significant nonprotein nitrogen fraction. Those extractable by salt represent, in addition, the globulins. Changes in these fractions induced by heat can be followed by simple solubility methods.
solution and of water, respectively. Several drops of chloroform mere added t o inhibit bacterial decomposition, and the mixtures were allowed to stand, with occasional shaking, for 16 t o 24 hours, and then filtered. Aliquot samples of the filtrates were analyzed (8) for nitrogen (semimicro-Kjeldahl). The amounts of nitrogen extracted in terms of percentage of total nitrogen are given in Table I. The variations in the solubility of the nitrogenous conatituents indicated that widely differing cooking conditions were used in the preparation of the meals.
Commercial Cottonseed Meals
Four of these meals were incorporated into otherwise complete rations in amounts sufficient t o furnish 12 per cent protein (N X 6.18). Male rats (Sprague-Dawley) a t weaning were furnished the diets ad libitum. The growth rates and food consumption data are presented in Figure 1and Table 11. Although the number of meals assayed is admittedly inadequate, the results suggest that, their nutritive value is in
I
TABLE I.
Men1 No. A Ba
2
Looahty
C
Da Eb
F
G H Ib Jb
Xb
Augusta Ga Augusta: Ga: Macon, Ga., Jackson, Miss. Ether-extd. cottonseed merrts (a)
Lb Mb
N” 00
protein content (N X 6.18), % 45.2 43.6 44.6 46.7 * 40.6 43.8 44.4 42.0 40.9 40.6 40.6 40.5 40.0 40.1 42.1 50-62
Total N Sol. in: 3% NaCl Water 46.7 7.8 45.3 8.4 8.3 42.7 38.0 6.7 35.8 5.9 35.2 7.3 9.2 34.7 6.3 34.4 34.0 6.1 33.0 5.9 31.9 6.0 30.0 6.6 27.2 5.9 7.5 22.0 9.6 7.1 75-SO
20-30
Used in growth experiments. b All samples sieved (20-mesh screen) except these.
5
Samples of commercial cottonseed meals were obtained from mills in fourteen different localities. Five-gram quantities were shaken with 200 ml. portions of 3 per cent salt 1
COMPARISON OF THE SOLUEJLITIES IN SODITJN CHLOWATER OF THE NITROGENCOMPOUKDS IN ConrMERCIAL COTTONSEED MEALS
RIDE AND IN
Present address, Western Regional Research Laboratory, Albany, Calif. Present address, Southern Regional Research Laboratory, New Orleans,
La.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1942
715
that a considerable portion of this fraction could be acProtein Av. ' Av. Crams Gain/ counted for as the albumin Weight Food ConGram Protein Cotton7 TotFl Meal in in Diet or water-soluble protein. Consumed seed dSd.in Diet", (N X 6.18), No. of Days Gain sumption, MealNo. 3% NaCl % % Animals Fed Gram; Grams Range Av. The globulin mixture was B 45.3 27.6 13.0 4 30 40 176 1.66-1.93 1.71 denatured slowly a t 100' and D 38.0 25.8 13.0 6 29 26 141 1.12-1.65 1.39 125 1.09-1.88 1 . 2 4 very rapidly a t 115' C . BeN 22.0 32.0 13.2 4 a0 20 0 9.6 28.6 13.0 4 30 21 143 1.01-1,23 tween these temperatures a The diets also contained Crisco, lS-l8.5%; sucrose, 61.0-66.0%; liver extract, 2%; salts, 2%; vitamin SUPwas a region in which the plements as described elsewhere (4). susceptibility of the proteins to changes in cooking conditions was apparently variable. The slight rise in nitrogen solubility observed between versely proportional to the amount of denaturation of protein 20 and 30 minutes of autoclaving a t 110" C. was reproducible. produced by the cooking. The increase in solubility on heating at 120' C. or above It may be pointed out that some of the discrepancies obwas noted in several experiments (also in Table 111) and served in previous nutritional studies of commercial cottonmay have resulted from hydrolysis of the proteins with the seed meals might be explainable in terms of these variations, consequent accumulation of water-soluble products. which have not heretofore been adequately appreciated. The experimental data plotted in Figure 2 are not directly comparable with commercial cooking practice. For example, Experimental Cooking ground or rolled meats subjected to sufficient steaming (3 In order to determine experimentally the changes in soluhours a t 100' or 45 minutes a t 108" C.) to bring the protein bility of the proteins during heat treatment, samples of a solubility to that of an average commercial meal contained uniform batch of ground cottonseed kernels (20 mesh) were appreciable amounts of unchanged gossypol as revealed by spread in thin layers on shallow trays and treated in a steamtheir extreme toxicity for rats. On the other hand, no free jacketed autoclave a t temperatures between 100" and 120' C. gossypol was detected in any of the commercial meals used in for time intervals varying from 10 minutes to 3 hours. The these investigations, as shown by equal growth increments intemperature was measured by a thermometer inserted into an duced by such meals before and after ether extraction. Apoutlet from the inner chamber and adjusted bv an escape valve. parently, commercial cooking procedures differ in one or more " T h e s'teamed particulars from the experiments described above. Inassamples were exmuch as wet heat alone (within limits) does not accomplish tracted with gossypol detoxication, the moisture content of the meats ethyl ether (12 during the heat treatment and the stirring to which they are hours in aSoxhlet subjected in the cookers are probably equally important extractor), dried, factors in facilitating physically the exposure of the cell conground, and asstituents to heat. sayed for nitroNot enough experiments with ground meats of differing gen and for solumoisture contents were made to permit the conclusion bilityof thenitrothat the results given in Figure 2 have more than relative genous material significance. They do indicate, however, that the cottonseed in salt solution proteins are extremely sensitive to temperature changes and water. The above 105-110" C. Such observations are in accord with the results of the salt solubility determinations are outlined graphically in Figure 2. Some of the FIGURE 1. GROWTH CURVESOF MALE RATS FED COMPLETE DIETSCONTAINwater-solubility ING COMMERCIAL COTTONSEED MEALS data are given W AS THE SOURCEOF PROTEIN (12 PER in Table 111. CENTLEVEL) 50 At least 20 per Figures in parentheses refer to number of rats 0 cent of the nitroaveraged. z een was con$ 40 0 verted into an insoluble form during the firat 10 minutes of & L heating. The data obtained with water extraction indicated TABLE 11. NUTRITIVE VALUEOF THE PROTEINS OF COMMERCIAL COWONSEED MEALS
*
30
c 4 I-
TABLE 111. EFFECTOF AUTOCLAVING ON WATERSOLUBILITY Y 20 OF NITROGENOUS CONSTITUENTS OF GROUND COTTONSEED I KERNELS 2 10Time Min.' 10
100' C. 10.0 9.9
% Total N Extracted5 105OC. llO°C. 116" C .
120° C. 11.3 12.9 20 ii:g 10.9 12.9 10.6 li:l 13.0 30 9.3 45 10.4 11.9 12.9 60 10:s l0:O 10.1 11.9 14.0 a The autoclaved meats were extracted with ether prior to the extraction with water. Before autoclaving, 25-30% of the total nitrogen was soluble in water.
..
..
W
I I
&
n . r
0
I
IO
20
!
! I
30 40 50 60 70 T I M E OF A U T O C L A V I N G I N M I N U T E S
80
90
FIQVRE2. E F F ~ COF T AUTOCLAVIN~ ON THE SOLUBILITY OF THE NITROQENOUS CONSTITUENTS OF GROUND COTTONSEED KERNELS IN 3 PERCENTSODIUM CHLORIDE SOLUTION The autoclaved meats were extracted with ether prior to the extraction with salt solution.
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Vol. 34, No. 6
feeding quality of t,heir cake and meal by analyzing at interTABLE IV. EFFECT OF TIMEOF STANDINQ AND ETHER EXTRAC- vals the nitrogen solubilities of the products TION ON SOLUBILITY OF NITROGENOUS COXSTITUENTS OF COMThe data in Table IV indicate that analyseci may be run 2 to MERCIAL COTTONSEED MEALS 3 hours after the meal is brought into contact with the 3 per % Total N Extd. by 3% NaCla cent salt solution. The mixtures filter readily; a mediumHours of Standing Run 1 Run 2 grade filter paper can be used. It is not necessary to remove 32.1 32.1 33.5 34.1 the residual oil before the extraction. Inarimuch as results 34.0 34.4 35.1 are calculated in terms of the ratio of soluble nitrogen to 36:8 35.5 total nitrogen present, no corrections for moisture or oil con% Total N Extd. by: tent need be made nor is it necessary to standardize the acid. Hz0 3% NaCl The data may be handled in terms of titration values. Thus A s received Ether extd. As received Ether extd. if 1gram of meal is equivalent to x ml. of acid in the Kjeldahl Meal B 7.7 8.3 46.4 45.3 Meal 0 7.0 7.0 9.3 9.6 analysis, and 20 ml. of the extract (5 grams meal in 200 ml. a The variations are within the limits of those which may be expected in solution) are equivalent t o y ml. of the same acid, the followsuch determinations; see also Oloott and Fontaine ( 8 ) . ing equation holds: recommendations of Thornton (6) that cottonseed be brought as quickly as possible to 225' F. (107.2' C.) and cooked for a short time or that, of two choices, it is better to cook for long periods and a t relatively lower temperatures than a t elevated temperatures for short times. Commercial meal PIT was obtained by the cooking method described by University of Tennessee investigators (6) in which relatively high temperatures are employed for short periods, contrary t o the above recommendation with which the experiments described here are in agreement. At least in so far as the nutritive value of the residual meal is concerned, the high-temperature cooking procedure requires further investigation. The observations described above lead to the suggestion that cottonseed millers may exercise some control over the
% total nitrogen extractable = 2CtOy/x The role of gossypol in the nutrition of cottonseed will be discussed in another publication. (1)
Literature Cited Olcott, H. S., and Bass, L. W., Cotton and C
