PRODUCTION OF PEANUT PROTEIN J. POMINSKI, W. 0. GORDON1, E. J. McCOURTNEY, H. L. E. VIX, AND E. A. GASTROCK SOUTHERN REGIONAL RESEARCH LABORATORY, NEW ORLEANS, LA,
S
EVERAL publications of this laboratory have described iaboratory scale (6) and pilot plant production (1, 8) of peanut protein from hexane-extracted peanut meal. Results in a laboratory investigation of processing variables (6), including a study of the effects of the water-to-meal ratio on the protein extraction and nitrogen solubility, indicated that successive peptizations of the extracted meal increased the yields of protein products. The present investigation was conducted to obtain pilot plant data on this system of protein extraction. Data are included on the effects of grinding meal before peptiza tion and the use of different mehhods and equipment in separating, dewatering, and drying the residual meals. Such data would be applicable in countercurrent systems of producing peanut protein. PREPARATION AND ANALYSES O F MEAL
The kernels of two lots of Spanish peanuts were treated with 0.5% lye solutios. for the removal of objectionable skin color (2,a). Each lot was extracted separately with hexane in this laboratory's continuous countercurrent extraction pilot plant (6),and a portion of one of the two meals thus obtained was finely ground. Chemical analyses made of the three materials are given in Table I and screen analyses in Table 11. The three materials were used in seven runs to produce peanut protein, Unground meal was used in five of the runs; the same ground meal in one run; and a different lot of meal in the remaining run.
trifuging. I n the remaining six runs methods and equipmaat varied. Figure 1 is a flow diagram of the general pilot plant procesa used in this work for the production of protein from solventextracted meal; Table I11 lists the machines used in each run. The variations can be summarized as follows: I n three runs (Nos. 5, 6, and 7) the meal was successively p e p tized by carrying out two extractions. After the first peptization the spent pulp was separated by screening (run 7) or centrifuging (runs 5 and 6) and then resuspended in water and separated again. I n runs 1 and 3, where there was a single peptization, the spent meal was separated from the extract liquor by screening and in the remaining runs 2 and 4 by centrifuging. I n the runs 1, 3, and 7, where screens were used, the extract liquor had to be further clarified in a centrifu e. Spent pulp was dewatered by either pressing and drying or 8rying directly. The precipitated protein waa separated by settling and centrifuging or by centrifuging directly. In all runs, the recovered protein was dried in a circulating air tray dryer a t 125' F. The quantities of meal peptized and the water-to-meal ratios used in each run are included in Table IV.
TABLE I. MEALANALYSES Total Nitrogen, Moisture, % 3.58
Lipids, % 1.85
As is Dry 9.44 9.79
I1
6:25
2:i8
8150 8:97
I (Ground)
Nitrogen Solubility', % As is Groundb 82.2d 88.1 87.2d 76.3 &:a
a Determined a t pH 7.5,40 to 1 water-to-meal ratio and at room temperature for 3 hours. b Meal ground to pass 60-mesh screen. After precipitation of protein from clarified peptized liquor by means of sulfur dioxide, 0.161 mg. of nitrogen/ml. remained in supernatant. d This value changed only approximately 1% when tap water instead of distilled water was used.
Methods. I n all seven runs to produce protein the meal was peptized at p H 7.5 ( 4 ) a t room temperature in a solution of sodium hydroxide using tap water; and the protein product was precipitated by adjusting the p H of the clarified liquor to 4.5 (8) with sulfur dioxide. Average analyses of the tap water by the Sewerage and Water Board of New Orleans in parts per million covering the period of time of the runs were as follows: sodium carbonate as CaCO8, 34.2; chlorides as C1, 14.5; sulfates as SO1, 44.2; dissolved solids on evaporation, 147.8; calcium as Ca, 17.8; magnesium as Mg, 5.2; and total hardness as CaCOs, 65.5. In a control run (No, I ) the methods and equipment (with the exception of pressing and drying of the spent pulp) were those previously reported (1). The procedures included peptization in one operation, screening and spray washing, drying, clarification by centrifuging, and recovery of protein by settling and cen1
IC
Meal
EXPERIMENTAL
%
TABLE IT. SCREENANALYSES U.5.
Mesh No.
Mea1 No* I* % Through Screen Unground Ground"
Meal No, I1 (Unground). % Through Soreen
a Prior to screening the meal was dried at 180. F. for 1.5 hours, washed with hexane, and air-dried to avoid diffioulties in sieving.
Present address, 8311 Rayford Drive, Los Angeles, Calif.
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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
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gases traveled concurrently with the feed. The feed entered the dryer from a cyclone after being mixed with hot gases from its exit end. I n the runs in which the liquor had to be further clarified by centrifuging, two types of centrifuges were used: One was a solid basket vertical centrifuge (International Size 3, Model F) operated a t a relative centrifugal force of 1000 times gravity. The other was a Multimatic DeLaval disk-type bowl, continuous, vertical centrifuge with mechanically operated valves; this was operated at a relative centrifugal force of 8500 times gravity. Protein which had been settled was recovered by centrifuging in the solid-basket vertical centrifuge. Without settling, the DeLaval Multimatic continuous centrifuge was used for recovery of the protein RESULTS
Peptization. Table I V shows the data obtained for each run. Successive peptizations gave the highest yields This operation gave a yield of 45.4% (run No. 5 ) s o2 as compared to 36.4% for the control run. In a single peptization, grinding the meal increased the yield from PRESS LIQUOR 35.3y0 (run No. 3) t o 44.8% (run No. 4). In runs No. 2 and 3, use of a horizontal centrifuge instead of screens and increase of water-to-meal ratio, respectively, did not appreciably affect the yield of protein m compared to that obtained in the control run Table V shows some effectsof using shaker screens and the horizontal centrifuge in separating spent pulp from the peptized slurry. For runs 1 and 2, where a single peptization was used, the pulp discharged from the horizontal centrifuge had a moisture of 471%, moisture-free D R I E D MEAL R E S I D U E D R I E D PRoTEIN basis, as compared to'801% for the average moisture of the pulp discharged from the meens. The ratio of Figure 1. Flow Diagram f o r Extraction of Peanut Protein solids in screen effluent to those in the centrifugal effluent was 13:l. Although an increase from 7.2 to 9.8 gallons per minute in rate of feed to the centlifuge did not change Equipment. The shaker screens are equipped with 40- and the moistuie content of the pulp discharge, the effluent solids I w m e s h screens BS previously described ( 1 ) . An 18 X 20 inch Bird continuous horizontal solid bowl centrifuge, operated at a relative centrifugal force of 1450 times gravity, was used for separating the meal USEDIN PILOT PLANT RUNS T ~ R E: I 111 EQUIPMENT from the extract liquor. Some comparative effects Protein Recoverya _ _ of using shaker screens and the horizontal centriHandling NO Meal Recovery Clar.floaof Centrifufuge in the separation of spent pulp are given in PeptiSolids Pressing tion piecipitated gal Table V. R u n No rations seprtiator machine Dryer Centrifuge protein separator i n runs I and 7 in which the residue solids had 1 1 Screens Davenport Rotary Basket Settled Basket Settled Basket . . . . . . . . DeLavalb 1 Bird 2 been recovered by screening, a Davenport press, 3 1 Screens . . . . . . . . . . . Basket Settled Basket 4 1 Bird . . . . . . . . . . . None Settled Basket sise No, 3-A, and a Hersey pilot plant size rotary 5 2 Bird ....... None Settled Basket pulp dryer were used. This dryer used an inter6 2 Bird , ,,. , , . . R'o'taiy None None DeLaval 7 2 Screens Davenport Rotary DeLaval None DeLaval mediate feed arrangement in which entering hot a All proteins dried in tray dryer. b
Only used to clarify a small portion of ext,ract liquor.
AND DEWATERING OF K,ESIDT!AL MEAL TABLE IT'. DATAo s PROTEINRECOVERY __________-Protein Recovery, %
Rim No
Type
I
1
i
5 '1
I I
Meal Pounds 100
241 49.8 140.5 140 192.6
I (Ground) I I I1 250.0 Feed t o sareens or oentrifuge.
Water-toMeal Ratio 10: I d 15: 1 30: 1 30: 1 15:le 10:1e,a 16:l
Spent Meal Recovery After MoisAfter Moisl ~ ~ ~ dture ~ separation, o %. t,ure Pressing, % separator, MoistureMoisturegal./min. As is free basis As is free bask 7 9 . 6 a91 5.1 88.9 801 ,. ... 7.2 82.5 471 ... 720 87.8 22.5 11.7 83.9 521 .. ... 8.01 86.7 652 .. 7.8f 87.9 727 5.3/ 90.7 975 77:4 342
... . I .
Protein On
basis of
original mealb 36.4 35.8 35.3 44.8 45.4
.. ..
Nitrogen in proteinc 16.47 16.68 16.66 16. OB 16.09 16.536 17.05h
Nitrogen on Basis of Original Nitrogen -~ Actual Calcd. 61 .S 61.0 64:6 60.1 66.1 73.5 74.6
76.4 73.2
..
..
..
..
Yield protsin (m.f.b.)/meal (m.f.b.1. ;Moisture-free-basis. A control r a n in which a n additional 6 : l ratio of spray washing was used. peptiastion; spent meal from first peptization was repeptiaed at 8ame water-to-mal ratios a s initial peptization exaept for run 6, where i t was . _e Successive . 0
c
d
I ( 1. 7
Y 8
Rates on feed material from second peptization. Meal washed in Bird centrifuge with additional 2.7:1 (total amount) ratio of water: Produot from first peptization, In succassive peptizations which yield one final uniform material, such a product would not be available.
April 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
increased from 0.3 to 0.4% by volume. In both types of separstion, shown in runs No. 5 and 7, where there was a second peptization, the percentage of moisture retained in the spent pulp increased. I n screening, the smaller partiele sizes retained the greatest amount of moisture. This is in contrast to centrifugation, for which the smaller the particle size, the less the amount of moisture retained (6).
Figure 2.
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minute. In run No. 4, in which ground meal and the horizontal centrifuge were used, a feed rate of 11.7 gallons per minute gave an effluent containing 0.9% solids by volume. Repasing this liquor through the centrifuge a t the same rate did not reduce the solids, but passing through the machine a t 7.8 gallons per minute gave 0.2 to 0.4% solids by volume in the effluent. Pressing. In the control run and in run 7, soli& over the 40and 150-meah screens were mixed uniformly before pressing. Approximately one third of the total solids passed through the 150-mesh screen, and in further clarification of the extract liquor with the solid basket centrifuge 2.5 gallons of peptized liquor were retained with the solids separated. Calculations showed 7.5 pounds of recoverable soluble protein in 36.7 gallons of liquid in the total pulp prior to pressing and 4.8 pounds in the 23.4 gallons of recovered press liquor. Spray washing thus did not appreciably remove the soluble protein remaining in the pulp from this run, since the nitrogen content was lowered from 5.573 to 4.375 mg. of nitrogen per milliliter, as shown in the press liquor. I n this run, the screened material was pressed a t a rate of 377 pounds per hour, and the pressed product was friable and crumbly.
Arrangement of Protein Pilot Plant
Shaker screens, tanks, a n d vertical basket centrifuge are in background
Claracation. Previous experience had shown that where the solid basket vertical centrifuge was used to remove fine solids from the screened extract liquors, solids in the effluent might go up to 4y0 by volume. In this work, using this percentage as a maximum limit, it was found unnecessary further to clarify effluent liquors from the continuous horizontal centrifuge. Increasing the feed rate t o the horizontal centrifuge increased the amount of solids in the centrifugal effluent and increased the moisture content of the solids discharge. I n run 6, where the feed waa washed in a horizontal centrifuge, the maximum wash rate that could be used without obtainiqg a solids discharge that was too wet was 0.93 part of water to 1 part of original meal when the feed entered a t a rate of 5.6 gallons per
Figure 3. Continuous Horizontal Centrifuge Used to Separate Solid Spent Meal Residues and Peptized Liquor from Slurries
Spent pulps from the horisontal centrifuge in runs 2, 4, 5, and 6, which contained fine solids (those passing a 150-mesh screen) could not be pressed. Thus fine solids prevented thedeweteringof spent meal residues, and sepsration of the fine material from spent pulp left a TABLEV. COMPARISON OF SCREENS AND HORIZONTAL CENTRIFUQE FOR material that was readily pressable. SPENTPULPSEPARATIONO Drying. The dried meals (runs 6 and 7) had a moisture content of approximately 2.5%. The products obtained were free flowing and contained no balls. I n run Ne. 6 the feed material to the dryer bad been obtained by mixing the unpressed wet pulp with dried material to obtain a moisture content Shaker Bcreens of 70.201, (2367$, moisture-free basis), and in run 1 1 5.1 88.3 758 91.4 1063 88.9 801 3.9 1 7 4.8 88.0 733 91.7 1105 ... 2.0 7, the pressed pulp with a moisture of 77.4% (342%, 2 7 5.3 90.4 942 94.2 1624 90:7 975 0.9 moisture-free basis) had been dried directly. No Horizontal Centrifuge difficulties were encountered in handling these .. 1 2 7.2 82.6 471 0.3 1 5 8.0 .. 83.8 feeds to the dryer. Approximate temperatures 517 0.3 .. 2 5 8.0 86.7 652 0.28 during drying were as follows: inlet gas, 525" F.; a Moistures on a moisture-free basis are not subtractable since liquor retained by the solid gas a t dryer discharge end, 245' F.; product, pulp contains considerable amounts of solubies which are not negll 'ble. . b Determined by centrifugation for 3 minutes a t a relative oentrggal force of 900 gravi144' F. ties. Moisture-free basis. Protein Recovery. Analyses of the dried protein products in Table IV indicate that a protein of C
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gated. The data obtained are applicable to countercurrent systems of peptization. The yield of protein was appreciably improved by the successive peptizations and also by grinding the meal before peptization. Successive peptizations gave a yield of 46.5% as compared to 36.4% using a reported method (1) in which spray washing was employed. Laboratory data can be used in calculating pilot pIant yields of protein. Peptized protein solutions can be clarified and precipitated protein can be continuously separated from protein slurries by use of a vertical centrifuge containing a disk-type bowl with mechanically operated valves. A horizontal centrifuge was more effective than screens in separating and dewatering undissolved solids from peptized slurries t o obtain a relatively clear effluent. The solids from the horizontal centrifuge could not be further processed for water removal by pressing due to fines present which pass a 150-mesh screen. Solids, from which these fines had been separated, were readily pressable. These pressed solids could be dried directly in a rotary dryer while those containing the fines had to be admixed with dried material before being dried. The dried products were free flowing and contained no balls.
Figure 4.
Pressed Meal Residue Is Examined Preparatory to Drying
lower nitrogen content is obtained on the second extraction of the unground meal. (The wet protein from the solid basket centrifuge varied from 36.0 to 43.4% in water content and that from the DeLaval centrifuge approximated 407,.) The actual and calculated yields (Table I V ) checked fairly well. Yields were calculated for runs 2, 3, 4, and 5 from a formula previously reported (6) using the laboratory data shown in Table I and pilot plant data for values of V,. Ti, is the ratio of milliliters of peptized liquor in the residue per gram of original meal and is equivalent to pounds of peptized liquor in the residue per pound of original meal. V , was 1.76, 2.84, and 1.46, for runs 2, 3, and 4, respectively, and varied with means of dewatering and particle size. The value of V , for run No. 5 was not required since the equivalent dilutiou of the successive peptization run was large enough to make negligible the amount of soluble nitrogen remaining in the spent pulp. Thus for a successive peptization run, the yield in the pilot plant may be calculated from Iaboratory data.
Figure 5.
Rotary Dryer Used for Drying Spent Meal Residues ACKNOWLEDGMENT
The authors wish to thank Vidabelle 0. Cirino and J. F. Jurgens for meal and protein analyses. LITERATURE CITED
(I) Arthur, J. C., Jr., Crovet,to, A. J., hlolaison. L. J., Guilbeau, W. F., and Altschul, A. M., J . Am. Oil Chemisfs’ Soc., 25, 398400 (1948).
SIGNIFICANCE O F DATA FOR A COUXTERCURRENT SYSTEM
It is apparent that these data are applicable to a stepwise countercurrent system. I n a countercurrent system a t least two shaker screens or horizontal centrifuges in series would be used instead of one machine for the two peptizations, and the peptized liquor from the second peptization would thereafter be used for the initial peptization of the meal.
( 2 ) Burnett, R. S., Chem. Eng. News, 24, 478-80 (1946). (3) Burnett, R. S., U. S. Patent 2,483,740 (March 8 , 1949). EWG. CHEM.,36, 164-7 (4) Fontaine, T. D., and Burnett, R. S., IXD. (1944). (5) Gastrock, E. 4., and D’Aquin, E. L., Oil M i l l Gaz., 53 (4), 13-21 (1948). ( 6 ) Pominski, J., Laborde, E. J., Cirino, V. O., Vix, H. L. E., J. Am. Oil Chemists’ Soc., 28, 508-12 (1951).
RECEIVED for review J a n u a r y 11, 1952.
SUMMARY
I n the pilot plant, practical methods of peptizing peanut meal and dewatering and drying of the spent residue were investi-
ACCEPTED February 21, 1962. Southern Regional Research Laboratory is one of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. 8. Department of Agriculture. T h e mention of trade names does not indicate a n endorsement by the U. S. Department of Agriculture oyer similar products not mentioned
