PROPERTIES OF PEANUT MEAL Influence of Processing Factors T. D. FONTALNE, CAROLYN SAMUELS, AND GEORGE W. IRVING, JR. Southern Regional Research Laboratory, U. S. D e p a r t m p t of Agriculture, New Orleans, La.
P
EANUT meal is ordinarily prepared from mechanically expressed press cake and at present is used almost exclusively as feed. One of the principal reasons that peanut meal is not more widely utilized industrially is the lack of sufficient specific information concerning the properties of the nitrogenous constituents of the peanut. This type of information is now being made available (3,4,6, 7), however, and has focused attention on the need for specifio information concerning the properties of peanut meal which result from controllable processing factors, including temperature, moisture, and duration of the treatment. The effect of these factors upon the peptizability of the nitrogenous constituents of cottonseed meal was investigated by Olcott and Fontaine (6),and a more detailed investigation of the heat denaturation of soybean meal proteins was reported by Beckel, Bull, and Hopper (1). For many potential industrial uses it is essential that the protein constituents of peanut meal be readily extractable and that the extracted protein be substantially undenatured. The treatments which peanuts receive during commercial hydraulic pressing for the removal of oil vary in severity, but are usually sufficiently drastic to denature the protein considerably and reduce markedly their extractability. I n view of these facts, it will be of economic value to peanut processors to ascertain the processing conditions under which adequate oil removal can be obtained with a minimum of alteration in the physical and chemical properties of the meal proteins. This investigation is coniined primarily to the determination of the effect of temperature, humidity, and length of processing treatment on the peptizability of the nitrogenous constituents of solvent-extracted peanut meal and of flaked raw peanuts. 0
MATERIALS AND METHODS
The work was carried out with a Pearl variety of peanuts, grown in 1940 and 1942. These white-skin peanut6 were selected because they afford certain advantages over the usual red-skin varieties for many industrial purposes (3). The peanuts bf both crops were stored in bags a t a Georgia Experimental Farm until they were received a t the laboratory, and were then stored in cotton mesh bags a t room temperature (25" C.). The peanuts of the 1940 crop were received in June, 1941; those of the 1942 crop were received in February, 1943. The experiments reported in this paper were begun in March, 1943. The peanuts were shelled, cracked, and flaked. After flaking, the peanuts of the 1940 crop were solvent-extracted with Skellysolve F (a naphtha solvent) to reduce the oil content t o about 0.3%. The solvent-free meal was ground and stored in screwcap jars. The flaked peanuts from the 1942 crop were stored in a metal container a t 4" C. until used. The meal samples, which were subsequently obtained by heat treatment of the solvent-extracted meal, are designated as meal 1 and those from the flaked raw peanuts as meal 2. The solvent-extracted meal and flaked peanuts were heated simultaneously for 0.5, 1.0, 1.5, 2.0, and 2.5 hours a t each of the temperatures and humidities investigated. A steam-jackete! autoclave was used to attain temperatures of looo, 105", 110 , and 118" C. and steam was admitted to the chamber containing the samples'in order to obtain 100% relative humidity (R.H.). To obtain 100% R.H. a t 80" C., a glass tray containing water was placed in a small oven, and the temperature was allowed to
The peptizability of the nitrogenous constituents of white-skin peanuts (Pearl variety) does not d s e r significantly from the usual red-skin varieties. Storage of white-skin peanuts at room temperature for two years before removal of the oil by solvent extraction does not alter the peptizability of the nitrogenous constituents of the meal. The effect of heat, humidity, and length of treatment on the peptization of the nitrogenous constituents of flaked peanuts and solvent-extracted peanut meal shows that the critical denaturation temperature for peanut protein in the meal, as measured by peptization, lies above 118" C. (dry heat) and above 80' at 100% relative humidity. The heat treatments routinely employed in a majority of the peanut oil mills are insufficiently controlled to prevent rather drastic denaturation of the meal protein. The data presented indicate that, with proper temperature and moisture control during processing, satisfactory oil removal can be accomplished with a minimum of protein denaturation.
reach 80" before the samples were introduced. To bbtain 0% R.H. at 100" and 118" C., the samples were heated in a vacuum oven at less than 1 mm. pressure. I n all of the experiments either 50 grams of solvent-extracted meal or 70 grams of flaked peanuts were spread in a thin layer on kraft paper to ensure uniform and rapid transfer of heat. The samples taken from the oven and the autoclave were kept a t room temperature (25" C.) for 3 days t o allow the moisture contents t o reach equilibrium with atmospheric humidity. The heat-treated flaked peanuts were then solvent-extracted with Skellysolve F and were subsequently freed of residual solvent. All samples were ground in a Wiley mill and were stored in screwcap glass bottles until used. Because of variations in the moisture content of the ground meal samples, it was necessary t o determine the nitrogen content of each meal at the same time that peptization experiments were carried out. The procedure for determining the percentage of total meal nitrogen peptized was described previously (4). Briefly, 2.5gram portions of the meal, contained in separate 200-ml. screwcap centrifuge bottles, were treated with 100 ml. of solvent. The suspensions were allowed to stand for 3 hours a t room temperature with occasional shaking and were then clarified by centrifuging. The pH values of the centrifuged solutions were determined by a glass electrode, and the total nitrogen was determined on duplicate aliquots by either the semimicro- or macro-Kjeldahl method. The nitrogen values reported in all tables and graphs were calculated on the basis of total volume of solvent added in each case. PEPTIZATION OF SOLVENT-EXTRACTED MEALS
The pH-peptization curves for unheated solvent-extracted meals 1 and 2 are shown in Figure 1. They are almost identical; in addition, there are no significant differences between the whiteand red-skin varieties (4). It is obvious, therefore, that the effects observed in the experiments to be described are due to the treatments employed and not to differences in the variety of peanuts or in the crop from which the sample was taken. The fraction of the total meal nitrogen peptized by water, 0.0025 N sodium hydroxide, and 1.0 M sodium chloride, for the meals obtained after each heat treatment, is recorded in Table I. It is apparent that there is close correspondence between the data for meals 1 and 2 when water, sodium chloride, and sodium hydroxide are used as peptizing agents. To simplify presentation of the results, peptization values for meals 1 and 2 with one peptizing agent (1.0 M sodium chloride) are plotted in Figure 2. The sodium chloride peptization values are considered the best and simplest measure of protein denaturation, since the degree of peptization in sodium chloride solution is less affected by varia-
625
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
626 TABLE I. EFFECT
O F TEMPERATURE AND HUVIDITY ON P E R C E N T A G E O F T O T ~ L SODIVM HYDROXIDE, .4ND 1.0 Jf S I T R O G E N PEPTIZED BY WATER, 0.0025 SODIlAI CHLORIDE F R O Y SOLVENT-EXTRACTED P E A N U T MEALS1 4 N D 2
Peptizing Agent
R.H.
%
Water
100 100 100 100 100 0
NaOH
100 100 100 100 100 0
NaCl
100 100 100 100 100 0
0
0
0
Temp.
c.
80 100 105 110 118 100 118 80 100 105 110 118 100 118 80 100 105 110 118 100 118
0.5Hour PH % Solvent-Ex 6 . 7 6 89.3 6.84 71.0 6 . 8 5 58.0 6.79 49.1 6.74 24.5 6.74 81.9 6.75 8 0 . 5 7.76 9 5 . 1 7.87 7 4 . 8 7.86 60.9 7.72 51.6 7.57 3 1 . 5 7.60 96.3 7.64 92.8 6.33 93.1 6.30 70.9 6.32 5 8 . 7 6 . 2 3 48.8 6.19 27.0 6.27 97.3 6 . 2 8 92.4
1.OHour PH '4
7.73 7.83 7.78 7.55 7.29 7.57 7.66 6.31 6.26 6.27 6.14 6.03 6.25 6.32
91.1 65.z 49.0 35.4 12.3 96.9 93.8 90.7 61.4 49.0 30.5 13.9 94.4 97.9
1 5 Hours PIT %
7.72 7.80 7.70 7.56 7.18 7.56 7.66 6.31 6.24 6.22 6.10 5.95 6.27 6.33
91.5 62.2 48.4 36.8 15.5 97.3 96.7 90.8 59.4 45.7 30.5 16.3 95.2 95.1
2 . 0 Hours -___ PH
73
2 . 5 Hours PH %
6.77 6.77 6.72 6.60 6.32 6.75 6.77 7.75 7.75 7.64 7.37 7.00 7.62 7.72 6.30 6.23 6.19 6.08 5.82 6.27 6.34
86.8 48.7 43.4 13.4 14.9 83.9 88.9 91.1 52.5 47.0 22.7 17.5 93.3 93.1 90.4 51.5 44.5 18.0 20.0 93.6 93.4
6.77 6.74 6.70 6.52 6.21 6.76 6.80 7.75 7.67 7.57 7.32 6.87 7.64 7.71 6.33 6.20 6.18 6.00 5.72 6.28 6.34
86.9 44.8 29.3 10.4 17.6 81.4 90.1 92.9 48.1 40.1 25.5 20.6 95.6 94.2 90.2 49.1 34.2 14.5 22.2 94.4 93.8
Solvent-Extracted Peanut Meal 2b 6.95 86.2 6.93 86.6 6.92 86.6 6 . 9 4 85.4 6 . 9 3 85.4 80 7 . 0 3 6 6 . 6 6.99 61.1 6.96 52.7 6.92 48.4 6 . 8 3 47.6 100 7 . 0 5 5 6 . 5 6 . 9 6 43.4 6.89 43.1 6 . 8 8 42.1 6.82 32.6 105 6 . 9 8 46.1 6 . 8 8 31.4 6.81 3 7 . 8 6 . 7 4 13.6 6.66 1 1 . 5 110 6.91 29.2 6.70 11.9 6.55 15.9 6.41 17.2 6.32 19.9 118, 6 . 9 8 8 8 . 8 6 . 9 6 89.1 6.99 88.5 6.97 8 9 . 5 6.94 87.6 100 6.95 8 8 . 1 6 . 9 3 85.6 6.94 8 7 . 1 6.92 88.3 6.94 8 8 . 4 118 NaOH 80 8.06 90.5 8 . 0 9 91.7 8.07 91.1 8 . 0 5 9 1 . 2 8 . 0 6 91.0 100 8 . 2 1 72.0 8.14 63.8 8.07 54.4 7.96 50.3 7 . 9 1 50.1 105 8.16 60.6 8 . 1 4 45.1 8.08 44.9 7.91 4 4 . 5 7 . 8 5 36.0 110 8.10 48.1 7.96 3 4 . 1 7.75 4 0 . 4 7.70 22.6 7 . 5 9 13.2 118 7 . 9 3 31.0 7.56 1 3 . 8 7 . 3 4 1 7 . 9 7.20 18.7 7 . 0 5 21.9 8.04 92.8 8 . 0 3 9 2 . 3 8.02 9 2 . 1 8 . 1 1 9 3 . 7 8.04 91.5 100 118 8.00 92.7 8 . 0 6 90.3 8 . 0 8 93.8 7.87 9 4 . 3 7 . 9 9 89.7 100 80 6 . 5 7 8 9 . 8 6.54 91.5 6 . 5 3 9 1 . 2 6.51 NaCl 100 6.57 66.5 6.53 80.9 6.49 5 3 . 9 6 . 4 3 100 105 6.58 55.6 6.49 44.8 6.44 43.9 6 . 4 0 100 6 . 4 8 48.3 6.37 33.3 6 . 3 3 37.4 6 . 2 4 110 100 118 6.44 3 0 . 1 6 . 2 1 15.2 6.10 19.6 5.94 100 100 6 . 5 8 8 8 . 8 6 . 5 7 86.6 6.57 91.1 6.54 0 118 6.55 9 3 . 8 6.55 91.6 6.56 9 4 . 1 6.55 0 water, pH 6.77, 90%; NaOH solution, p H 7.75, a Corresponding values for meal 1, unheated: 94.8%; NaCl solution, pH 6.33, 95%. b Corresponding values for meal 2, unheated: water, pH 6.95, 88.8%; NaOH solution, p H 8.08, 93 47'. NaCl solution p H 6.55 92.8%. Heat treatments were carried out on flaked raw peanuts wdichDkere solvent-extraoted beiore peptization measurements were made. Water
.
100 100 100 100 100 0 0 100 100 100 100 100 0 0
tions in the pH of the meal-solvent suspension than are the peptization values obtained with the other solvents investigated (Table 11). It is obvious that, in 1.0 M sodium chloride-meal suspensions, changes in pH similar in magnitude to those found in the experiments reported in Table I have an almost negligible effect upon the amount of nitrogen peptized. The peptizability of the nitrogenous constituents of heattreated solvent-extracted meal 1 does not differ materially from that of heat-treated flaked peanut meal 2, except, possibly, after treatment at 110' C. and 100% R.H. for 1.5 hours where slightly higher peptization values are obtained in the case of meal 2 . This increase was also observed in cottonseed after 0.5-hour treatment a t 110' C. and at 100% R.H. ( 5 ) . It is significant that heating for as long as 2.5 hours a t 100' and 118" C. and 0% R.H., or a t 80" C. and 100% R.H., results in only a slight change in the peptizability of the protein of peanut meal and meats. At higher temfieratures, however (118' C. and 100% R.H.), the peptization values indicate that complete denaturation of peanut protein is attained rapidly. By contrast, soybean protein shows considerable denaturation after 2.5-hour heating a t 720" C. and 0% R.H. and also after 2.5-hour heating a t 80" C. and 100% R.H. (1). The results in Figure 2 indicate that, after prolonged heating of peanut meal and meats, there is a slight but gradual increase in the amount of peptizable nitrogen. This increase is probably due to protein degradation. The amount of nitrogen peptized by 1 .O 3f trichloroacetic acid (nonprotein nitrogen) was determined for several of the meals which had been heated for 2.5 hours at
Vol. 36, No. 7
various temperatures (Table 111). The increase in the'nonprotein nitrogen content of the heated samples paralleled the increase in severity of the heat treatment a t 100% R.H. At 0% R.H., however, there was little change in the nonprotein nitrogen values, indicating, as would be expected, that in the absence of water no protein degradation takes place. I n hydrochloric acid suspensions at pH 4.20 to 4.25 of the heated peanut meals described, significantly less nitrogen is peptized than in 1.0 Af trichloroacetic acid suspensions. This unusual behavior is noteworthy, inasmuch as nitrogenous substances which are soluble in 1.0 Jf trichloroacetic acid are generally considered to be nonprotein in character, this difference in solubility is widely used analytically to determine the relative amounts of protein and nonprotein nitrogen in mixtures. The occurrence in urine of a protein soluble in trichloroacetic acid solution waq recently reported ( 2 ) . PEPTlZATlON OF HYDRAULlC-PRESSED MEALS
The practical significance of the results presented above are apparent when compared with similar data on samples of meal taken during a carefully controlled 3-day mill run in which 330 tons of peanuts were crushed for oil ( 3 ) . The flaked peanuts were heated for approximately 15 minutes in each stack of a four-stack cooker. The temperature of the cooked meats upon leaving each of the stacks was, respectively, 80°, 95", 107", and 110" c. Samples A-512, 8-513, and -4-514 (Table IV), representing daily composites of the meal produced on each of three succeeding
P"
Figure 1. pH-Peptization Curves for Solvent-Extracted White-Skin Peanut Meals -x-x-,
1940 crop; -.eo-. 1942 crop
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
July, 1944
I
I 0
I
627
I
0 TlME IN HOURS
TlME IN HOURS
Figure 2. Effect of Temperature, Humidity, and Length of Treatment on PeptizabiIity 9f Nitrogenous Constituents of Flaked Raw Peanuts (left) and of Solvent-Extracted Peanut Meal ( r i g h t ) in 1.0 M Sodium Chloride The heat-treated flaked peanuts (left-hand graph) were extraeted with Skeliysolve F before peptization measurements were made.
days during the test run, and thirteen other commercial peanut meals were examined with res by 1.0 M sodium chloride s the three meals obtained from duced under milder cooking c meals except 0-143. It is also treatments routinely employed in a majority of the peanut oil mills are insufficiently controlled to prevent rather drastic denaturation of the meal protein, as indicated by markedly decreased protein peptizability.
I t is important to note that meal 0-143 probably represents the best example of what can be consistently produced by careful control in an oil mill, as far as the quality of the protein is concerned. Although oil content of this meal is relatively high (Q%), the peptizati properties of the meal compare favorably with those of solvent-extracted meal. When these facbs are the results in Table I, it is logical to conclude that b perature and moibture were carefully controlled in the on of meal 0-143 and that satisfactory oil removal was accomplished with a minimum of protein denaturation. The present work and previously published results (7) point to TABLE 11. TOTAL NITROGEN OF UNHEATED SOLVENT-EXTRACTED the conclusion that critical denaturing temperatures for peanut PEANUT MEAL, PEPTIZED BY 1.0 M SODIUMCHLORIDEAT protein are above 118" C. (dry heat) and above 80" at 1 0 0 ~ o VARIOUSDH VALUES R.H. Since there appears to be little need for excessively high ,---Meal 1 temperatures and moisture contents t,o rupture the oil cells of the Total N PH peptized, % peanut, it $odd seem advisable to employ in the mill the lowest 5.53 94.8 5.65 89.6 moisture content and lowest temperature compati hle with ade5.80 94.3 6.00 92.8 quate oil removal. In this manner the meal proteins can be pre6.10 95.4 6.35 93.3 6.33 95 0 6.55 92 8 served in a substantially undenatured state and thus be available for wider industrial utilization. TABLE 111. TOTAL NITROGENSOLUBLEIN 1,O M TRICHLOROACETIC ACID FOR SOLVENT-EXTRACTED MEALS HEATED2.5 ACKNOWLEDGMENT HOURSAT VARIOUSTEMPERATURES AND HUMIDITIES" of Total NThe authors wish to express their appreciation to Alva F. Faust R.H., % Temp., C Meal 1 Meal 2 and R. H. Robinson of the Analytical, Physical Chemical and 80 '00 5.23 5.59 Physical Division of this laboratory for making a considerable 5.44 100 5.97 100 1 00 105 5.83 6 19 number of the nitrogen determinations reported in this paper. 110 6.58 100 6.61
------.
7-%
1is 7.05 8 16 100 5.62 5.64 0 a Total nitrogen soluble in 1.0 M trichloroacetic acid for unheated meals: meal 1, 5.65%; meal 2,5.83%.
100
TABLEIV.
TOTALNITROGENPEPTIZED BY 1.0 M SODIUM COMMERCIAL HYDRAULIC-PRESSED MEALS
LITERATURE CITED (1)
Beckel, A. C., Bull, W. C., and Hopper, T. H., IND. ENG.CHEM.,
(2)
Beckman, W. W., Hiller, A., Shedlovsky, T., and Archibald, R.
(3)
Burnett, R. S., and Fontaine, T. D., IND. ENQ.CHEM.,36, 284-8
34, 973-6 (1942).
CHLORIDE FROM
Sample No. 4-512 -4-513 A-514
0-101 0-102 0-103 0-104
0-105
pH 6.16 6.18 6.18
Tote1 N Peptized, ?% 68.0 64.6 64.6
6.03 6.06 5.75 5.70 6 03
59.8 53.5 41.1 39 0 48.6
Sample No. 0-106 0-107 0-108 0-109 0-120 0-121 0-133
pH 6.03 6.05 5.90 5.98 6.25 6.10 6.14
Total N Peptized, % 39.7 51.3 37.9 60.2 60.2 46.6 35.5
0-143
6.62
85.7
M., J . B i d . Chem., 148, 247-8 (1943). (1944).
(4) Fontaine, T.D., and Burnett, R. S., Ibid., 36, 164-7 (1944). ( 5 ) Higgins, B. B., Holley, K. T., Pickett, T. A., and Wheeler, C. C., Ga. Agr. Expt. Sta., Bull. 213, 14-18 (1941). (6) Olcott, H. S., and Fontaine, T. D., IND.ENO.CHEM.,34, 714-16 (1942).
(7) Pickett, T. A., Ga. Agr. Expt. Sta., Circ. 142, 1-8 (1943). PRmraromm before the meeting of the bmeriaan.8il Chemiats' Sooiaty, New Orleans, La., 1943,
