PEPTIZATION OF NITROGENOUS CONSTITUENTS OF
Solvent-Extracte Peanut
1
T. D. FONTAINE AND R. S. BURNETT Southern Regional Research Laboratory,
U. S. Department of Agriculture, New Orleans, La. removed from the meal by aeration. The meal was ground in a Wiley mill to pass a 50-mesh sieve and was then stored in tightly sealed tin cans at 25" C. A small amount of material, largely skins, which failed to pass the sieve was discarded. The extracted meal contained 10.68 per cent moisture, 8.19 per cent nitrogen, 0.36 per cent lipides (petroleum ether extract), and 4.55 per cent ash.
More than 80 per cent of the nitrogenous constituents in solvent-extracted peanut meal is peptized upon the addition of water (pH 6.6). Minimum peptization occurs i n the pH range 3.5 to 5; more than 80 per cent of the total meal nitrogen is peptized a t pH 1.5, and more than 90 per cent a t pH 7.2 and above. Calcium, barium, and magnesium chlorides (0.25 to 1.0 &-) are effective peptizing agents at pH values between 5 and 6. At lower concentrations they decrease the amount of nitrogen peptized in the pH range 6 to 9. Sodium and potassium salts i n general (except fluorides and acetates) are good peptizing agents at 1.0 N concentration. The twenty-seven salts investigated appear to offer no advantage over weak alkali (pH 7.2) as to the amount of nitrogenous constituents peptized. The importance of considering pH as well as salt concentration in evaluating peptizing agents for the nitrogenous constituents o f peanut meal is emphasized.
EFFECT OF SOLVENT pH ON PEPTIZATIQN
To determine the influence of p€I of solvent upon the peptization of the nitrogen in the meal, separate portions of the meal were treated with water and with varying concentrations of sodium hydroxide and hydrochloric acid in the following manner. The method used is similar to that previously described for soybean ( 5 ) and cottonseed ( 3 ) . Portions of the meal (2.5 grams), contained in separate 200ml. screw-capped centrifuge bottles, were treated with 100 ml. of solvent. To facilitate wetting, the meal was first stirred with approximately 10 ml. of the solvent before addition of the remainder. The meal suspensions were allowed t o stand for 3 hours a t room temperature (25" C.) with occasional shaking. Preliminary experiments demonstrated that continuous agitation is not necessary for the attainment of equilibrium. The suspensions were clarified by centrifugation for 15 minutes in a field exerting a relative centrifugal force of nine hundred times gravity at the bottle tip. For suspensions in the pI-1 range immediately on either side of the minimum peptization point it was necessary to centrifuge for 15 minutes a t 3500 relative centrifugal force to clarify the suspensions.
A
T P R E S E S T oil is removed from the peanut by mechanical
expression. The press cake remaining contains 5 to 9 per cent of oil and is used largely as a source of protein in livestock feeds. A wider industrial utilization of this proteinrich by-product of the peanut oil industry has not been feasible because specific information is lacking concerning the properties of the many components of the peanut. There is also no information as t o the effect of the treatment received in meal processing on these properties. Conversion of the peanut oil-pressing industry to more efficient and more readily controlled solvent-extraction processes has been hindered by the large installations of pressing equipment already in operation and by the apparent inapplicability of available solvent-extraction processes to peanuts. It remains to be demonstrated whether solvent extraction of peanuts will provide a meal that is sufficiently superior to the press meals to justify the expense of installing the required equipment. A knowledge of th. nature and properties of the nonoleaginous constituents of the peanut is becoming increasingly necessary if better utilization of this expanding southern crop is t o be realized. An extensive investigation of the chemical and physical properties of these constituents and of pressed and solvent-extracted meals is in progress a t the Southern Regional Research Laboratory. The information obtained is being applied both in the development of better methods of removing the oil and in the development of such products as adhesives, fibers, plastics, paper coatings, and cold water paints One phase of this work is presented here.
TABLEI. EFFECT OF pH OF SOLVENT ON PEPTIZATION OF NITROGENOUS CONSTITUENTS OF SOLVENT-EXTRACTED PEANUT MEAL HCl Added per Gram Meal, Millimoles 2.62 1.61 1.11 0.80 0.60 0.40 0.20 0.10 0.06 0.03 0 (water)
70 of Total p H of Sus- Meal N pension
Peptized
1.54 1.97 2.50 3.10 3.56 4.32 5.18 5.76 6.04 6.27 6.64
84.5 78.7 57.3 21.5 10.2 7.7 10.6 17.8 31.4 50.5 83.5
IiaOH Added per yo of Total Gram Meal, p H of ,Sua- Mea! N Millimoles pension Peptlzed 0.05 0.15 0.21 0.31 0.42 0.94 2.19
7.17 8.32 8.80 9.50 10.05 11.28 11.77
92.5 94.0 95.0 95.2 97.8 98.2 98.0
The p H values of the centrifuged solutions were determined by a glass electrode. All pH's reported are observed values. No salt correction was applied above pH 9.0 since the presence of various salts in unknown amounts in the meal makes impossible an accurate calculation of the proper correction. Because of the low salt concentration in all cases, however, the correction would be small. Total nitrogen was determined by the macro-Kjeldahl method on aliquots of the clear centrifugates, and the nitrogen values reported in Table I were calculated on the basis of the 100-ml.
PREPARATION O F PEAhUT MEAL
A composite sample of a single hybrid variety of peanuts (Virginia Runner, male X Improved White Spanish, female), grown in 1940 at the Georgia Coastal Plains Experiment Station, Tifton, Ga., was used in the present investigations. The peanuts were mechanica,lly shelled in October, 1941, and the shell fragments were carefully removed. After refrigeration at 4' C. for 18 hours, the cold nuts were ground in a sausage mill. The oil was extracted from the ground meats by percolation with petroleum ether (boiling range, 30" to 60" C.), and the residual solvent was
164
INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1944
165
the pH of suspensions between pH 5.5 and 6.5 result in large differences in the amount of nitrogen peptized. This fact may account for some of the apparent discrepancies in the literature for the amount of peanut meal nitrogen peptized by water alone. Although peanut meal is a fairly effective buffer, differences in the pH of the water used in making suspensions can produce significant differences in the pH of the suspension. Furthermore, suspensions made with freshly prepared peanut meals frequently exhibit higher pH values than suspensions made with meal that has been stored for some time. However, if the p H of the suspension is considered and controlled, the amounts of nitrogen peptized for a given pH value in fresh and stored meals are practically identical. For example, a sample of the meal used in obtaining the data of Table I was stored in a closed container at
Figure 1. pH-Peptization Curves for Solvent-Extracted Meals -0-0-
Ij
*
peanut;
-- --
volume of solvent added in each case. The results in Table I are compared graphically in Figure 1with published data obtained by the s a m e p r o c e dure for solventextracted soybean (4) a n d c o t t o n seed (3)meals. Table I and Figure 1 show that more than 80 per cent of the nitrogen i n solvente x t r a c t e d peanut meal is peptized upon the addition of water (pH 6.6). Minimum peptization occurs in the pH range 3.5 t o 5 , and more than 90 per cent of the total n i t r o g e n of t h e meal is peptized a t pH 7.2 and above. In these respects peanut meal closely r e s e m b l e s soybean meal but differs m a r k e d l y from c o t t o n s e e d . The curve for peanut meal illustrates the importance of careful pH control in investigating the peptization of the nitrogenous constituents of this meal. Small differences in
soybean ( 4 ) ;
cottonseed (3)
a-.-
I
Figure 2. Total Meal Nitrogen Peptized b y 0.25, 0.5, and 1.0 N Salt Solutions (except 1.0 N NaF) as Compared to Acid or Alkaline Solutions at Same pH Shaded areas, when on top, indicate decreased peptization by added salts; unshaded areas, when o n top, indicate inoreased peptization by added salts.
100
KHCOJ ..,
100
__
n
r
NaF
KF
NaE
NaCl
LS2OS
NaI
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INDUSTRIAL AND ENGINEERING CHEMISTRY
room temperature for 11months. The peptization of the nitrogenous constituents a t p H 4.2, 7.9, and 9.0 was then determined. The values found were 7.8, 92.1, and 93.4 per cent, respectively. The figures in Table I agree closely with those reported recently by Higgins and associates ( 1 ) who studied the peptization of the nitrogen in several samples of solvent-extracted peanut meal over a more limited range (pH 6.98 to 7.24). The inability of these investigators to find a correlation between peptization and p H can be attributed to the fact that they were working in the pH range of maximum peptization where small changes in p H do not show up as differences in peptization. Of the seed meals which have been investigated in this manner, only two others-namely, tepary and soybean (5)-appear to exhibit as high a peptization of nitrogen on the addition of water alone as is found in the peanut.
containing sodium dihydrogen phosphate, potassium dihydrogen phosphate, and sodium metabisulfite lie within this pH range and yet the amount of nitrogen peptized is relatively low. Magnesium sulfate and sodium dithionite are only slightly less effective peptizing agents than are calcium, magnesium, and barium chlorides. The sodium, potassium, and lithium halides (except fluoride), sodium and potassium sulfates, sodium thiosulfate, and sodium salicylate are inferior in peptizing power to the preceding salts but are effective peptizing agents a t certain concentrations. Sodium and potassium acetate and the fluorides and bicarbonates of these metals, as well as disodium hydrogen phosphate and sodium sulfite, either have no effect or actually decrease the amount of nitrogen peptized.
loo
EFFECT OF SALTS ON PEPTIZATION
Vol. 36, No. 2
s
The amount of nitrogen peptized in solutions containing different concentrations of various salts is given in Table 11. Salt solutions of the concentrations indicated were prepared and equilibrated with the meal, and the nitrogen peptized was determined by the procedure described. The results are presented in Figure 2 to compare the amount of nitrogen peptized by different salt concentrations with that peptized without the addition of salt a t the corresponding pH. The latter results were estimated by interpolation from the curve for peanut meal in Figure 1.
OF SALTSON PEPTIZATION OF NITROGENOUS TABLE11. EFFECT CONSTITUENTS OF SOLVENT-EXTRACTED PEANUT MEAL
pH of Suspension and % ’ of Total Meal Nitrogen Peptized -0.25N-0.5Nr--l.ONSalt PH % PH % PH % 6.15 36.9 6.50 37.8 NaF 6.24 4 1 . 3 6.17 6 3 . 1 6.09 89.5 NaCl 6.08 82.8 6.05 86.7 6.10 49.3 NaBr 6.15 8 5 . 0 6.14 83.7 6.16 7 5 . 1 NaI 7.30 37.1 6.85 37.4 6.60 3 4 . 3 KFa 6.22 59.7 6 . 2 3 87.0 KCla 6.16 38.5 6.26 91.1 6.25 82.1 6.20 47.8 KBra 6.32 88.6 6.38 91.7 KIa 6.25 67.5 5 . 9 5 50.8 5.82 86.3 LiCl 6 . 0 5 37.1 6.14 85.8 6 . 1 5 87.2 6.20 6 8 . 8 NanSO4 6.32 88.2 6.34 86.8 6.30 6 3 . 3 K&04a 5.63 90.6 MgSOa 5.68 34.5 5.60 4 9 . 3 5.26 87.0 5.40 49.6 5.50 36.2 MgClz 5.00 75.3 5.15 32.2 5 . 1 0 41.6 BaCh 5.00 41.0 5.04a 84.65 5.10 28.6 CaClz 6.90 38.0 7.18 43.4 6.67 33.6 Na acetate 7.35 48.4 7.06 4 1 . 8 Na acetatea 6.80 3 7 . 3 7.02 41.5 7.32 50.8 6 . 7 8 35.7 K acetatea 4.95 18.7 4.72 24.7 5.20 17.0 NaHnPOa 4.95 27.2 5.15 20.3 5.33 17.3 KHzPOs 8 . 0 7 91.0 8.30 91.0 7.80 90.6 NazHP04 7.90 90.4 7.90 90.1 7.85 8 6 . 8 NaHCOa 8.37 91.5 8.26 90.6 8 . 1 3 88.9 KHCOaa 8.50 90.6 8 . 2 7 90.3 8.08 91.0 NanSOa 6.58 97.8 6.46 93.7 6 . 3 5 91.0 Na salicylate 6.17 89.8 6.17 89.6 6.17 86.1 NasSzOa 5.25 79.2 3.98 31.6 3.82 23.3 NaaSaO4 4.37 27.7 3.75 25,o 4 . 7 5 25.9 NanSzOs 0 Determinations made on meal after storage for 11 months. All others made on freshly prepared meal.
...
0
...
The most effective salts used for the peptization of the nitrogenous constituents of peanut meal were calcium, barium, and magnesium chlorides. They peptize approximately eight times as much nitrogen in 1.0 N concentration, and approximately three times as much nitrogen in 0.25 N concentration, as is peptized at the same p H values in the absence of the salts. The effect does not result entirely from the fact that the pH values of the suspensions containing these salts lie close to the minimum peptization range (pH 3.6 to 5.2) where larger increases mgiht be favored. This is substantiated by the fact that meal suspensions
4
Figure 3. Total Meal Nitrogen Peptized by 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, 0.25, 0.5, and 1.0 N Salt Solution as Compared to Acid or Alkaline Solutions at the Same pH Shaded areas, when o n top, indicate decreased peptization by added salts; unshaded areas, when on top, indicate increased peptization by added salts.
The results indicate that salts of sodium and potassium are about equal in effectiveness as peptizing agents. I n the case of the halides, the amount of nitrogen peptized increases in the order fluoride, chloride, bromide, iodide. It is noteworthy that 1.0 N solutions of sodium salicylate p e p tize as much nitrogen a t pH 6.6 as is peptized in strongly alkaline solutions (pH 11) in the absence of the salt. From a practical standpoint it is significant that more than 80 per cent of the total nitrogen of peanut meal can be peptized between pH 5.0 and 6.2 in 1.0 N solutions of such salts as sodium chloride, bromide, iodide, and sulfate, lithium chloride, magnesium sulfate and chloride, and calcium chloride; less than 45 per cent of the total nitrogen can be peptized in the same p H range if these salts are not added. The importance of considering concentration, and particularly pH, in evaluating peptizing agents cannot be overemphasized. This is evident in the results given in Figure 2. Conditions must be carefully controlled and the results critically examined to avoid the erroneous assignment of peptizing properties to certain compounds. Thus, if pH were not considered and conclusions mere based entirely upon the amount of nitrogen peptized under a given condition, then disodium hydrogen phosphate, sodium sulfite, sodium bicarbonate, potassium bicarbonate, etc., whose solutions contain high percentages of the total nitrogen, might be regarded as effective peptizing agents; whereas it is obvious that they are less effective than dilute sodium hydroxide solutions
INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1944
161
IO0 D
WN
90
6
80
gI70 0
z
E
60 50
40
TABLEIV. EFFECT OF 0.04 N SOLUTIONS OF CALCIUM, BARIUM, AND MAGNESIUM CHLORIDES AT DIFFERENT p H VALUESON PEPTIZATION OF NITROGENOUS CONSTITUENTS OF SOLVENTEXTRACTED PEANUT MEAL
830 20
Acid or Alkali per Gram Meal, Millimoles
pH of Suspension and % of Total Meal N Peptized -CaCla---BackVMgC1-
%
PH
PH
%
PH
%
Hydrochloric Acid Added
Figure 4.
pH-Peptization Curves for Solvent-Extracted Peanut Meal in 0.04 N Salt Solutions A CaCla;
0 BaCIz; X MgClz; 0 no added salt.
2.62 1.61 0.60 0.40 0.20 0 (water)
1.70 2.14 3.65 4.15 4.72 5.38
85.7 82.2 19.1 14.0 14.2 14.8
1.68 2.15 3.70 4.16 4.65 6.45
84.0 82.4 18.1 14.8 15.0 16.5
1.72 2.15 3.70 4.25 4.85 5,80
86.7 84.0 15.6 12.7 13.4 16.5
6.60 8.05 8.82 9.25 10.20
18.6 26.0 28.2 27.8 80.6
Sodium Hydroxide Added
of the same pH. Similarly, a t a concentration of 0.25 N , sodium chloride would not be considered an effective peptizing agent while, a t a concentration of 1.0 N , sodium chloride definitely increases the amount of nitrogen peptized. These facts make it difficult to compare the present results with those previously reported in the literature ( I , 8) for peanuts. EFFECT O F SALT CONCENTRATION ON PEPTIZATION
The effect of lowering the concentration of several of the most effective peptizing agents upon the amount of nitrogen peptized was determined. The results are given in Tables I1 and 111 and in Figure 3. All four of these salts-namely, calcium, barium, and magnesium chlorides and magnesium sulfateexhibit a similar tendency to reduce the amount of nitrogen peptized in extremely low concentrations (0.01N ) . This tendency is more apparent in the case of the magnesium salts than in the case of calcium and barium chlorides. However, a t salt concentrations between 0.02 and 0.04 N the amount of nitrogen peptized is approximately equal to that peptized a t the same pH when no salt is added; a t higher concentrations, progressively increasing amounts of nitrogen are peptized as compared with solutions of the same pH when no salt is added. At still lower concentrations of these salts it would be expected that peptization values approaching those obtained with water alone would be obtained.
0.10 0.21 0.42 0.94 2.19
6.25 7.78 9.12 10.55 11.50
16.7 17.8 20.8 70.7 91.7
6.60 8.16 9.25 10.75 11.60
17.4 20.2 24.8 75.6 90.0
These results indicate that in low concentration calcium, magnesium, and barium salts decrease the amount of nitrogen peptized in the pH range 6 to 9. I n high concentrations these same salts are among the most effective agents for increasing the amount of nitrogen peptized in the pH range 5 to 6. Knowledge of this behavior may be of considerable value in the commercial extraction of peanut proteins. DISCUSSION
The results presented illustrate the typical peptization behavior of the nitrogenous constituents of solvent-extracted peanut meal under simple reproducible conditions. I n considering the applicability of the data to possible industrial purposes, however, certain points should be borne in mind. The suspensions used in these investigations were rather dilute as the meal to solvent ratio was 1 to 40. The peptization data represent the amount of nitrogen present a t equilibrium in the total volume of solvent added and not the amount of nitrogen that can be extracted or removed under these conditions. This is due to the fact that, after centrifuging, the meal retains a fraction of solvent together with the nitrogen which it has peptized. Under all extraction conditions, however, the amount of recoverable nitrogen will be TABLE111. EFFECT OF CONCENTRATION OF CALCIUM, BARIUM, less than, but proportional to, the amount of peptized nitrogen. AND
MAGNESIUM SALTSON PEPTIZATION OF NITROQENOUS CONSTITUENTS OF SOLVENT-EXTRACTED PEANUT MEAL pH of Suspension and % of Total Meal N Peptiaed
?-or mality
0.01 0.02 0.04 0.06 0.08 0.10
-CaCl-
PH
%
5.55 5.38 5.25 5.22 5.20 5.17
12.0 12.0 14.6 16.3 18.4 20.4
-BaClz-
PH
%
5.65 5.50 5.34 5.28 5.25 5.23
11.8 12.6 14.7 16.4 18.0 20.0
-MgCln
PH
%
6.00 5.90 5.75 5.70 5.65 5.60
20.0 16.0 16.9 18.4 20.0 22.3
-MgSO4-'
PH
%
6.96 5.88 5.78 5.74 5.72 5.70
21.2 18.2 18.6 22.0 24.7 27.1
ACKNOWLEDGMENT
The authors wish to express their appreciation to B. B. Higgins, Georgia Agricultural Experiment Station a t Experiment, Ga., for the hybrid peanuts used in this work; and to W. A. Reeves and R. R. Mod of this laboratory for a number of the analyses reported. LITERATURE CITED
EFFECT O F pH ON SALT PEPTIZATION
The amounts of nitrogen peptized over a wide p H range by 0.04 N solutions of calcium, magnesium, and barium chlorides are shown in Table Iv and Figure 4. A concentration of 0.04 N was selected because of its proximity to the minimum peptiza-
(1) Higgins,B. B., Holley, K. T.,Piokett, T. A., and Wheeler, C.D., Ga. Expt. Sta., BUZZ.213, 14 (1941). (2) O'Hara, L. P.,and Saunders, F., J . A m . Chem. Soo., 59, 362 (1937). (3) OlCott, H.s.9 and Fontaine, T.D.9 Ibid., 61,2037(1939). (4) Smith, A. K., and Circle, S.J., IND.ENG.CHEM., 30,1414 (1938). (6) Smith, A. K., Circle, S. J., and Brother, H. G . , J . A m . Chem. SOC.,60,1316 (1938). \
