Improvement in the Color of Peanut and Cottonseed Proteins T. D. FONTAINE’, S. B. DEIWILEIP, JR.1, AND G. W. IRVING, Jr.’ Southern Regional Research Laboratory, U. S. Department of Agriculture, New Orleans, La.
T
HE suitability of a given
ever, attempts to prepare a Data are presented to show that protein preparations can l i g h t colo r e d protein from be obtained from the meals of white-skin peanuts and preparation of protein meal of red-skin peanuts have blanched red-skin peanuts, without the use of bleaching for industrial use depends met with little succew beupon its color, solubility, visagents, that are as light or lighter in color than commercause of the presence of the cosity characteristics, tackicial samples of soybean protein. The color of proteins highly pigmented skins. ness, and adhesive strength. prepared from meals of unblanched red-skin peanuts and Whereas most of the pigThe relative importance of cottonseed is improved considerably through the use of ment in the peanut is coneach of these properties or controlled protcin extraction and precipitation techniques centrated in the skin, the combinations of them is deand by washing the moist protein precipitates with orhighly pigmented portions of termined by the particular ganic solvents such as dioxane, acetone, and methyl ethyl the cottonseed occur as pigapplication of the protein. ketone. Procedures are given for obtaining, from meal of ment “dots” which are disI n products such as fibers, unblanched red-skin peanuts and from cottonseed meal, tributed throughout the seed. films, paper coating adhesatisfactory yields of protein preparations that are lighter The spectrophotometric sives, gummed tape adhein color than those obtained heretofore from similar raw nature of some of the pigsives, flexible glues, cold water materials, and that approach in color very close to the ments contained in these pigp a i n t s , plywood glues, range of practical usefulness for the production of adment dots has been investiplastics, and related products, hesives and fibers. The use of heat in dryiqg is shown to gated by this laboratory (1, the ideal balance between exert inappreciable influence upon the color of dried pea2). Expression of the oil these properties must be denut protein. from cooked cottonseed does termined experimentally. not remove any appreciable Several of the properties amount of color, and the solubility of the proteins is greatly mentioned have been considered in detail in previous publications decreased (14). Solvent extraction of cottonseed with ethyl -for example, reports on the factors that influence peptization of ether removes a large percentage of the pigments but is not protein in solvent-extracted and hydraulic-pressed peanut meal economically feasible. While petroleum naphtha can be used (4, 8) and cottonseed meal (9, 16). As a result of experiments commercially as a solvent for removal of oil from cottonseed, described previously (IO), conditionshave been defined for producthis solvent does not remove an appreciable amount of color and ing hydraulic-pressed peanut meal from which the protein is the resulting meal is highly pigmented. readily extracted in high yield; once isolated, this protein has a Results are presented here to show that light-colored proteins high degree of solubility. can be prepared not only from white-skin and blanched red-skin Viscosity data on relatively concentrated solutions of peanut peanuts, but also from unblanched red-skin peanuts by controland cottonseed proteins were reported recently (6),together with ling the extraction conditions and pH of protein precipitation. data on the working range of solutions of modified and unmodiLight-colored proteins have been obtained also from cottonseed fied peanut proteins a t various concentrations, temperatures, by washing the freshly precipitated protein with various organic and pH values. This information has made possible the developsolvents. ment of peanut protein preparations that are suitable for the proPEANUT SKIN EXTRACTS duction of fibers, gummod tape adhesives, and flexible glues (3,6). Preliminary spectrophotometric examination was made of exFor many industrial purposes lack of color in protein preparatracts from peanut skins, which are responsible for most of the tions is not only advantageous but frequently a prerequisite to color in the meal. White skins were extracted with sodium their successful application. The present publication is conhydroxide (pH 12.2), and red skins with both sodium hydroxide cerned primarily with the methods developed for obtaining lightand 95y0 ethanol. colored proteins from peanuts and cottonseed and the applicaSpectral transmittance measurements of these extracts were tion of the trichromatic system of the International Commission made with a Coleman spectrophotometer (Model 10s DM, on Illumination in evaluating the color of these and soybean nominal slit width 7.5 millimicrons), using cells 1.27 cm. thick proteins. and either 95% ethanol or 0.02 N sodium hydroxide as a referThe seed coats of some varieties of peanuts are almost devoid ence standard. Determinations were made a t each 10 milliof color while others vary from light to deep red or even to dark microns between 380 and 770 millimicrons except where the purple. When peanuts are not blanched, as is usually the case in curves were flat, when some interpolations were made. commercial processing,the seed coat remains in the meal after the Figure 1 shows the results. There are no distinctive absorpoil is removed. I n the case of white-skin peanuts the presence tion bands in curve A for the alkali extract of white skins. of the seed coat in the meal is of no consequence since nearly pure The curve is relatively flat, since the extract had almost no color. white protein can be readily obtained from such material. HowOn the other hand, curve B,for the corresponding extract of red 2 Present address, Bureau of Agricultural and Industrial Chemistry. skins, show$ moderate absorption in the blue region, and has Beltavilie, Md. distinctive absorption bands at about 420 and 500 millimicrons. 2 Bureau of Agricultural and Industrial Chemistry, Washington, D. C .
-
1232
INDUSTRIAL A N D ENGINEERING CHEMISTRY
December, 1945
TABLEI. Protein No.0 1 2 3 4
ISOLATION OF PEANUT, COTTONSEED, AND SOYBEAN PROTEIN PREPABATIONS
Skim
Red
6 6
Red Red White Red Red
9
32 Red
10
Red
11 12 13 14 15 16 17 18 18A 18B 18C 18D 19 19A
Red White Red Red White Red Red Red Red Red Red Red Whjte White Red Red Red Red Red Red Red Red Red Red Red Red Red Red
20
20A 21 21A 21B 21C 22 22A 22B 22C 23 23A 23B 23C
Blanched No
Yea Yea No No
Yes Yes No NO Yes Yea No
No No No No No No No No No No No No No
Meal Usedb PE-17 HP-16 PE-17B PE-18 HP-11 HP-16 PE-17B PE-17 HP-11 HP-16 P PE-17B al8
PE
PE PE PE PE PE PE PE PE PE
PE PE PE
No
PE
No No No No No No No No No No No No
PE PE PE PE PE PE PE PE PE PE PE P E
Extraction Precipitation Agent pH Agent PH Peanut Preparations 4.8 Water HCI Water HCl 4.8 Water HC1 4.8 Water HCl 4.8 NaOH 918 HCL 4.8 NaOH 9.2 HCl 6.4 NaOH 9 . 8 HCl 4.8 NarSOr 7.6 HCl 4 NesSOr 7.4 HC1 5 .. 8 4 NatBOa 7.6 HC1 5.4 4.8 NatBO: NarSOa 7.6 HCI HCl NaOH 7 . 0 CHICOOH 6.0 NaOR 7.0 801 6.0 NaOH 7.0 HCl 6.0 NaOH 11.0 80s 4.6 NaOH 7 . 8 80: 6.0 NaOH 7.0 80t 6.0 NaOH 7.0 8Ot 6.0 7.0 $Or 6.0 NaOH 7.0 8Or 6.0 NaOH NaOH 7.0 Sot 6.0 NaOH 7.0 HCl 6.0 NaOH 7.0 HCI 6.0 7.0 HCI 4.6 NaOH NaOH 7.0 HCl 4.5 NaOH 8.2 HCl 6.6 NaOH 8.2 HC1 5.6 8.2 HCl 6.6 NaOH NaOH 8.2 HCl s.6 NaOH 8.2 HCl 4.6 NaOH 8 . 2 HCl 4.6 NaOH 8.2 HC1 4.6 NaOH 8.2 HC1 4.6 NaOH 10.0 HCl 6.6 NaOH 10.0 HCl 5.5 NaOH 10.0 HCl HCl 6 NaOH 10.0 66 ,. 5
..,.
..
Drying Agent Air 2S0 C Air: 2 5 O C: Air 2 6 O C Air)25'C: Air: 26O C. Air, 25" C. Air 26O C Air' 26* C' Air: 26O C: Air, 28' C. Air'26' Air 25O C C' Air: 2 6 O C: Air 2S0 C Air: 25O C: Air, 26O C. Air, 2 5 O C. Ethanol Lyophyliaed e Vacuum aOo C. Vacuum' 60° C. Air, SOO'C. Air, 2 6 O C. Ethanol Air 2 5 O C. Etdanol Air 2 5 O C. Didxane Acetone
ketone Air 2 6 O C. Didxane Acetone Methyl ethyl ketone Air 26O C. Didxane Acetone Methyl ethyl ketone
1233
tion, thirteen samples of cottonseed protein were prepared from petroleum- and ethyl-ether-extracted meals. Water, sodium chloride, sodium sulfite, and sodium hydroxide were the extracting agents at pH values from 6.3 to 11.0. Hydrochloric and acetic acids and sulfur dioxide were used to prec;pitate the protein at pH values from 7.0 to 4.0. Since some question had arisen as to the effects of drying upon color, certain of the foregoing samples were dried after precipitation by methods shown in Table I. The stability of the pigments to heat was determined by drying in different ways and a t various temperatures. Portions of the same moist protein cake were washed with various organic solvents not only to remove water, but also to ascertain the most effective method of removing color. Ethanol, dioxane, acetone, and methyl ethyl ketone were chosen because the pigments were soluble in these solvents. Six samples of commercially produced soybean protein also were included in the investigation for comparison.
SPECFROPH~TOMETRIC EXAMINA-
SOhltiOIlS Of the various proteins were prepared for ketone spectrophotometric analysis by dissolving 100 mg. in 25 ml. of 0.02 N ... ... 7.0 A$, 25' C. sodium hydroxide (pH 12.2). Oc... ... 4.0 Air, 26" c. casionally it was necessary to centri... 4.0 Air 2S0 C. fuge to obtain clear solutions of 4.0 Didxane ... . . .. ... 4.0 Acetone peanut and soybean proteins; for ... ... 4.06 Air 2 6 O C. clear solutions of cottonseed protein .... .. 4.0 Didxane 4.0 Methyl ethyl>etone it was nearly always necessary to .. ... 4.0 Acetone centrifuge. Protein solutions having ... ... 4.0' Air 26O C. transmittance readings of less than .. . ... 4.0 Didxane .. . ... 4.0 Methyf ethyl ketone 98% at lo00 millimicrons were con4.0 Acetone sidered too cloudy for proper evaluation. Spectral transmittance measa Protein numbers 1-12 correa ond to those of Table IV in a former ublication (4). were made as previously P E denotes petroleum-ether &kellysolve F o r Bbextracted meal: EE,ethyl-ether-ertracted meal; HP, hydraulic-predned meal. described for the analysis of the peaFroren then dried In vacuo. nut skin pigments. d Protei; precipitated at p H 4.0 then washed one time with water a t p H 4.8. e Protein washed one time with water. Figure 2 shows representative I Methods of preparation unknowm to authors. transmittance curves (400 to 700 millimicrons). They are essentially smooth. The curves for proteins Curve C, for the ethanol extract of red skins, is unlike curve B in 5, 8, and 26 indicate that considerable pigment was retained that it has two plateaus at 410-450 and about 570 millimicrons. in the protein, whereas proteins 4, 7, and 30 show only slight To determine the cause of this difference, a portion of the ethanol pigmentation, extract was dried at 65' C. in vacuo, and the solids were comCOLORIMETRIC EVALUATION OF SoLmioNs. Although specpletely redissolved in sodium hydroxide a t pH 12.2. The transtrophotometric data are recognized rn the fundamental basis for mittance curve for this solution (curve P ) has the same general the specification of color, even to an experienced observer they permit no more than a qualitative comparison of the chromaticishape and absorption minima, as does curve B; this indicates that ethanol extracts the same pigment(s) or pigment precursors as ties of various materials. To obtain a graphical comparison of does alkali, and possibly that the absorption characteristics of the colors of the foregoing protein solutions, the spectrophotothese alcohol-soluble compounds are altered in the presence of metric data were therefore converted, by means of I.C.I. trialkali. stimulus values (11,M),into trichromatic coefficients. Standard illuminant C, an approximation of average daylight, was ISOLATION AND EXAMINATION OF PROTEINS chosen &s the source of radiation. Table I1 lists the trichromatic By the methods indicated in Table I, forty-two samples of coefficients x, y for a number of peanut protein preparations. peanut protein were isolated from petroleum-ether-extracted and Data for all protein preparations are shown in F i p r e 3. hydraulic-pressed meals prepared from blanched and unblanched Many workers prefer to conceive of color in terms of a monored-skin peanuts and unblanched white-skin peanuts. In ad&chromatic system of color specification rather than in terns of a 6 . 4 HCI NaCl 1 N NaCl'1 N 6 . 4 HCI NaCI' 1 N 6.4 HCl NaCI: 1 N 6.4 HCI Cottonseed Preparations 26 EE NaOH 11.0 HC1 26 EE NaOH 11.0 HC1 27 ... PE NaOH 11.0 HC1 NaOH 11.0 HCl 27A .. PE 27B PE NaOH 11.0 HCl 28 EE NaCl 0 5 N 6.3 HCI 28A ... EE NaC1'0'5N 6 . 3 HCI 28B ... E E NaCl'0'5N 6.3 HCI 28C EE NaC1:O:SN 6.3 E C l 29 PE NaCl.0.5N 6.3 HC1 29A PE NaCl 0 6 N 6 . 3 HCl NaC1:0:5N 29B PE 6.3 HCI 29c PE NaC1,0.6N 6.3 HCI Soybean protein8 30, 31, 32, 33, 34, 35, commercial products!
24 24A 24B 24C
Red Red Red Red
No No No No
.
...
...
PE PE PE PE
4 0-4 8 d Air 25O C. 4:0-4:8 Didxane 4.0-4.8 4.0-4.8 Aoetone
TION OF SOLUTIONS.
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
1234
Vol. 37, No. 12
+
It is unnecessary to specify the third coefficient, b, since r b = 1. The brightness (or luminosity or transmittance) is defined as the ratio of the total energy passing through the
Q
+
three filters to the energy incident upon them. I n the particular case of the I.C.I. trichromatic system the three filters or primary stimuli are imaginary, as is the observer, who has fixed powers of visual perception. The trichromatic coefficients x, y, and z are calculated from spectrophotometric data. Accordingly, to aid in the interpretation of results, the trichromatic data were converted to the psychophysical values of luminous transmittance, dominant wave length, and purity (19, 16). These values are listed in Tables I1 and 111. Since only a few dominant wave length and purity values are given in Table 11, it is necessary to refer to Figure 3 for additional data, where lines of dominant wave length and purity have been superimposed upon the chromaticity diagrams. I n interpreting the chromaticity diagrams, it should be remembered that the lower the colorimetric purity of the protein solution and the nearer its 5, y plot approaches the plot for illuminant C, the less color it has.
t
01 380 Figure 1.
1 I
I
I
I
I
1
I
1
460 540 620 700 WAVE LENGTH-MILLIMICRONS
100
I
780
Spectral Transmittance Curves for Peanut Skin E x t r a c t s
A.
Sodium hydroxide extraat of white skins Sodium hydroxide extract of red skins Ethanol extract of red skins D . Ethanol extract of red skins evaporated to dryness, and pigment redissolved in sodium hydroxide
I
B.
C.
80
w
u z
2 i-
5 60 v)
z a trichromatic system. I n a monochromatic color system it may be considered that the specimen is compared with heterogeneous radiation, such as average daylight, combined with homogeneous (monochromatic) radiation, the wave length of which can be varied a t will. The intensity of the heterogeneousradiation, and the intensity and wave length of the monochromatic radiation, are adjusted until a match is obtained. The color is then defined in terms of its luminosity (total radiation required to produce the match), dominant wave length (wave length of the monochromatic radiation), and purity (ratio of monochromatic to total radiation). I n a trichromatic color system it may be imagined that a colored specimen is illuminated by light from a standard source, such as average daylight. Light from the same source also passes through three standard primaries or filters (aa red, green, and blue) and is then recombined into a single beam. The amount of light passing through each filter (R for the red filter, G for the green, and B for the blue) is independently adjusted until the sample is matched. Then the chromaticity of the specimen is defined as
‘=R+G+B
andg =
G R+G+B
E
g40 W
0
U
2 20
I
400
I
I
I
480 560 640 WAVE LENGTH-MILLIMICRONS
I
720
Figure 2. Spectral Transmittance C u r v e s for Alkaline Solutions of Peanut, Cottonseed, and Soybean Proteins 4 6 7 8 13. Peanutproteins Zb. dohonseed protein 30. Soybaan protein (Curve numbem cornempond t O protein numbem in
’
Table I)
As the pigment concentration increases, there is a progressive shift to longer dominant wave lengths. This phenomenon was previously observed to occur a t wav; lengths longer than 570 millimicrons by Newhall and associates (la) in the cme of the Munsell colors and by Detwiler and associates (7)in the case of soybean oils containing varying concentrations of carotenoid pigments. OPTIMUM COLOR C O N D I T I O N S
TABLE11. ILLUSTRAT~VE I.C.I. TRISTIMULUS DATA ON The calculated values given in Tables I1 and I11 and shown ALHALINB SOLUTIONS OF PEANUT PROTEIN PREPARATIONS graphically in Figure 3 for the trichromatic coefficients (z and y) Protein
No.0
4
Z
1 0.3661 2 0.3180 3 0.3181 4 0.3198 6 0.4123 Correspond t o those
Y
0.3684 0.3289 0.3302 0.3337 0.3940 in Table I.
Luminous Transmittance. %
Dominant Wave Length, rns
68.3 96.9 96.6 97.1 49.1
578.6 671.0 570.0 570.0 581.4
purity,
%
2z:g 5.8 7.2 48.3
and for the psychophysical values of luminous transmittance, dominant wave length, and purity show the differences in color between the white- and red-skin peanut and cottonseed proteins prepared under different conditions. The protein obtained from unblanched white-skin peanuts was lighter than that prepared from unblanched red-skin peanuts but was no better in color than the protein prepared from blanched red-skin peanuts. The
December, 1945
INDUSTRIAL AND ENGINEERING CHEMISTRY
proteins prepared from white or blanched red-skin peanuts had about t,he same color characteristics as did tht. samples of commercial soybean protein that were examined. Cottonseed protein, in contrast to peanut and soybean proteins, is generally much more highly colored. The effect of bleaching agents has been investigated only indirectly in these experiments-namely, in those cases where sulfur dioxide was used for protein precipitation, or where sodium sulfite was used for extraction of the protein and sulfur dioxide was accordingly liberated whcn the extracts were acidified to precipitate the protein. This mild treatment with sulfur dioxide does improve slightly tho color of the protein obtained from white-skin peanuts and from blanched red-skin peanuts by precipitation a t or near the pH of minimum protein solubility (compare proteins 2 and 10, 3 and 11, 4 and 12); but it exerts no bleaching action upon the color of the protein obtained in a similar manner from unblanched red-skin peanuts (compare proteins 1 and 8). The results in Tables I1 and I11 and Figure 3 make it obvious that, with two exceptions, none of the treatments employed for the separation of protein from the meal of unblanched red-skin peanuts was so effective as blanching in improving the color of the final product. However, in the case of proteins 13 and 14, prepared from the meal of unblanched red-skin peanuts by extraction a t pH 7.0 and precipitation of the protein a t pH 6.0 with acetic acid and sulfur dioxide, respectively, the proteins were lighter in color than were those prepared by precipitation with hydrochloric acid a t pH values lower than 6.0 (compare proteins 13 and 14 with 20). I n the case of the protein precipitated a t pH 6.0 also, sulfur dioxide exerted an appreciable bleaching action. The improvement in protein color obtained by precipitation a t pH 6.0 was probably due to the elimination in the final product of part of the seed-coat pigments, inasmuch as proteins 15 and 19, prepared from practically unpigmented white-skin peanuts by precipitation a t pH 6.0,had practically the same color characteristics as proteins 4 and 12 prepared from the same material by precipitation at pH 4.8. Apparently, the red-seed-coat pigments of the peanut are more soluble a t pH 6.0 than a t pH 4.5 or are less strongly adsorbed on the protein a t pH 6.0. The yield of protein obtained by precipitation a t pH 6.0 was approximately three fourths of that obtained by
1235
A- COTTONSEED PROTEIN
0.310 0.310
1
I
I
0.320
x
I
I
0.330
-
I
0.
0.340
I
1
0.335 0.335 Figure 3.
I
"0.375
I
0.415
1
x
I
0.455
I
I
0.495
I
0
Chromaticity Diagram for Alkaline Solutions of Peanut, Cottonseed, and Soybean Proteins
The lower the colorimetrio urity of the protein aolution and the nearer its r,y plot mpproaohes tge plot for illuminant C, the l e m m color it ham.
1236
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 37, No. 12
The colorimetric data on the cottonsocd protein preparations given in Table 111and Figure 3 show that in only one case was a light-colored protein obtained without additional treatment. I n this case (protein 28), the protein was precipitated at pH 4.0 from a sodium chloride extract of ethyl-ether-extracted cottonseed meal. Subsequent washing of the moist protein cake with organic solvents further improved the color, dioxane and methyl ethyl ketone being slightly more effective than acetone (compare proteins 28, 28A, 28B, and 28C). The best of the cottonTABLE 111. L u ~ r ~ oTRANSMITTANCE os OF ALKALINE SOLUTIONS seed proteins (28A and 28B) compare favorably in color with some samples of peanut and soybean protein (Figure 3). OF PEANUT, COTTONSEED, AND SOYBEAN PROTEIN PREPARATIONS Luminous Luminous Luminous Protein 29, prepared from petroleum-ether-extracted cottonProtein Transmit- Protein Transmit- Protein Transmitseed meal under exactly the same conditions as protein 28, was No.0 tance, % No.0 tance, % No.. tame, % much darker in color than the latter. As shown in Figure 3 for ---Peanut-Cottonseed---Peanut26 67.8 19 95.3 1 68.3 proteins 29A, 29B, and 29C, washing of this moist protein cake 19A 95.8 26 65.1 2 95.9 27 41.9 with solvents was relatively more effective in reducing the 20 67.2 3 96.6 27A 61.3 20A 67.1 4 97.1 amount of color present than was solvent washing of the protein 45.5 21 57.4 5 49.1 28 27B 84.5 21A 69.0 6 91.5 prepared from ethyl-ether-extracted meal. However, since the 28A 87. e 21B 62.6 7 92.9 initial color of protein 29 was high, the best of the solvent-washed 87.6 21c 63.1 8 59.7 28B 86.3 22 61.7 9 66.0 proteins obtained from i t (29A) was markedly inferior in color to 29 61.9 22A 74.5 10 93.5 29A 78.4 22B 65.4 11 94.1 those of the 28 series. Similarly, the color of cottonseed protein 29B 78.4 22c 67.6 12 95.6 prepared from alkaline extracts of petroleum-ether-extracted 23 53.9 28C 77.5 13 84.9 62.8 14 91.6 meal was greatly improved by washing with dioxane (compare 23B 23A 56.2 .--Soybean15 95.3 30 90.3 23C 59.7 16 58.0 proteins 27 and 27A), but since the initial color of protein 27 was 31 96.2 24 82.5 17 68.2 extremely high, the solvent-washed product was considerably 32 93.1 24A 86.3 18 85.5 33 92.0 24B 89.0 18A 86.4 darker than the proteins of the 28 series. It may be concluded, 54 94.4 24C 87.1 18B 85.7 a5 92.5 18C 85.2 therefore, that the best conditions found in these experiments 18D 84.8 for obtaining cottonseed protein with a color which approaches a Protein numbers correspond t o those in Tables I and 11. that of commercial proteins consists in the dioxane washing of the moist protein cake obtained at p H 4.0 from a sodium chloride extract of ethyl-ether-extracted cottonseed meal. precipitation at pH 4.5. Thus i t is possible by this method to obtain from the meal of unblanched red-skin peanuts good yields of protein which is only slightly inferior in color quality to that obtainable from meals of white-skin or blanched red-skin peanuts, and which approaches in color close to the range of practical usefulness for the production of adhesives and fibers.
As illustrated by protein 24 (Figure 3), a light-colored protein comparable in color to that obtained by extraction at pH 7.0 and precipitation at pH 6.0 (protein 13) was also obtained from iunblanched red-skin peanuts by extracting the meal with 1.0 N sodium chloride. The sodium chloride extract was diluted with an equal volume of water, and the protein was precipitated at pH 4.0. The color of this protein was further improved by washing the moist protein cake with various solvents as shown by 24A, 24B, and 24C (Figure 3). Although the lightest of the solvent-washed proteins (2418) was slightly lighter in color than the best of the proteins prepared by alkali extraction of meal from unblanched red-skin peanuts, none of the solvent treatments yielded proteins with such good color as proteins prepared from white or blanched red-skin peanuts. The effectiveness of ethanol, dioxane; acetone, and methyl ethyl ketone in removing color from various peanut proteins was investigated in some detail (Table I11 and Figure 3); it was considered of considerable practical value to determine if lightcolored protein could be prepared from the protein of unblanched red-skin peanuts precipitated at low pH values (between 4.0 and 5.5), which result in higher yield and greater ease of handling. Although significant improvement in the protein color was obtained by washing with any one of these solvents, and particularly with dioxane (compare proteins 21 and 21A, 22 and 22A, 23 and 23A), none of the solvent-washed proteins precipitated a t pH 4.5 or 5.5 from alkaline extracts of meal of red-skin peanuts wm so light in color as protein prepared by precipitation a t pH 6.0 or protein from meal of blanched or white-skin peanuts. These results show that, if the peanut proteins are extracted at alkaline pH values in the presence of red skins and precipitated at pH 4.5 or 5.5, the pigments either react with the protein or are so strongly adsorbed by it that solvents cannot remove the major part of the color. Under the conditions investigated, the method of drying the protein obtained from meal of unblanched red-skin peanuts has no appreciable influence upon its color (compare proteins 18, MA, 18B, 18C, and 18D, Figure 3).
ACKNOWLEDGMENT
The authors wish to express their appreciation to Dorothy Nickerson, Color Measurements Laboratory, Agricultural Marketing Administration, U. s. Department of Agriculture, for her helpful suggestions in the preparation of this paper; to Morrice Curet and Carolyn Samuels for many of the calculations;, to Charlotte Boatner for suggesting the use of dioxane; to W. D. Harris, Agricultural and Mechanical College of Texas, for suggesting the use of acetone; and to R. S. Burnett and A. L. Merrifield €or supplying some of the proteins used in these experjments. LlTERATURE CITED
(1) Boatner, C. H., Oil & Soap, 21, 10 (1944). (2) Boatner, C. H., Caravella, M., and Samuels, C. S., J . Am. Chem. Soc., 66,838 (1944). (3) Burnett, R.S.,IND. ENO.CHEM.,38, 861 (1945). (4) Burnett, R.S.,and Fontaine, T.D., Ibid.. 36,284 (1944). (5) Burnett, R. S., Parker, E. D., and Roberts, E. J., fbid., 39, 982 (1945). (6) Burnett, R. S.,Roberts, E. J., and Parker, E. D., Ibid., 37, 276 (1945). (7) Detwiler, S. B., Jr., Bull, W. C., and Wheeler, D. H.,Oil & Soap,20, 108 (1943). (8) Fontaine, T. D.,and Burnett, R. S., IND.ENQ.CHEM.,36, 164 (1944). (9) Fontaine, T. D., Irving, G. W., Jr., and Markley, K. S. (un-
published results), (IO) Fontaine, T. D., Samuels, C. S., and Irving, G. W.,Jr., Zbid.,
36,625 (1944). (11) Hardy, A. C., “Handbook of Colorimetry”, Cambridge, Technology Press. (1936). (12) Judd, D.B., J . O p t . Soc. Am., 23,359 (1933). (13) Newhall, 9. M.,Nickerson, D., and Judd, D. B., Ibid., 33, 385 (1943). (14) Olcott, H.S.,and Fontaine, T. D., IND.ENQ.CHEM,,34, 714 f 1942).
(15) Olo&-H. S.,and Fontaine, T. D., J. Am. Chem. Soc., 61,2037 (1939); 62,1334,3519 (1940). (16) Opt. SOC.of Am., Colorimetry Cornm., J. Am. Opt. Soe., 33,544 (1943).
