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INDUSTRIAL A N D ENGINEERING CHEMISTRY
ceeds the cost of cornstarch, it is very much lower t,han the current market price of wheat starch (5 cents per pound) and is considerably less than the price of cornstarch (3.46 cents per pound). The starch produced from wheat by this process is of better color, contains less protein, and gives more viscous pastes than the average commercial wheat starch now available on the market. One large industrial processor has found it t o be excellent raw material for the production of sirups and sugars. While the wheat germ is not extracted in the pilot-plant procedure, there is no reason to believe that i t could not be recovered in continuous-plant operation and used for the production of wheat oil and oil meal. The fiber and oil meal, along with some gluten, could be used &s feed. The gluten recovered in this
Vol. 36, No. 5
process has lost its dough-forming characteristic as a result of the sulfur dioxide treatment but still remains a source of protein. An industrial producer of monosodium glutamate has found that the protein presenc in the gluten fraction gives the usual yield of glutamate, but that its low protein content makes it an unsatisfactory raw material for the commercial process. LITERATURE CITED
(1) Eynon, L., and Lane, J. H., “Starch, Its Chemistry, Technology, and Used’, p. 139, Cambridge, W.Heffer & Sons, Ltd., 1928. (2) Hopkins, C. Y.,Can.J . Research, 11, 751-8 (1934). (3) U. S.Tariff Commission, “Starches, Dextrines, and Related Products”, p. 42, Washington, Govt. Printing Office, 1940. P R E ~ E N Tbefore E D the Division of Agricultural and Food Chemistry at the 106th Meeting of the AMERICAN CHEMICAL SOCIETY, Pittsburgh, Pa.
TERNARYSOLVENTS FOR ZEIN
CYRIL D. EVANS AND RALPH H. MANLEY1
I
N THE commercial utilization of zein for coating purposes, the solvents are usually blends of two or more components formulated to meet the requirements of particular operating conditions. A study of ternary solvent systems for zein is, therefore, of practical interest because it affords data which can be used in controlling the rate of evaporation of solvent mixtures; it also provides a means of improving the compatibility of other resinous materials and plasticizers with zein-solvent systems, and offers opportunities to reduce the cost of binary solvents by the addition of low-cost diluents. Primary and binary *solvents for zein have been investigated by the authors (2, 6) and by Swallen (IO). There is little t o be found in the literature, however, on ternary solvents for zein, with the exception of some observations reported by Galeotti and Giampalmo in 1908 (4) on the solubility of zein in five ternary mixtures, all of which included ethyl alcohol and water as the binary zein solvent. The present work was undertaken to supplement earlier studies on primary and binary zein solvents in order that the general characteristics of ternary solvents for this protein might be available. The zein was from the batch used in earlier studies on primary and binary solvents (2, 6). I n all instances the protein was dried to constant weight in vacuum at 55” C. before use. The method of measuring its “critical peptization temperature”, or the temperature above which the zein is soluble in all proportions and below which it is soluble only to the extent of 2 or 391,, was previously described. Since small amounts of impurities in the solvents used were found to have a marked effect on their peptizing capacity, great care was exercised in their purification. Peptization temperatures were readily reproducible to within 1”C. I N BROADEST terms, solvents for zein may be classified as primary solvents, which are capable in themselves of dispersing zein; secondary solvents, which are not solvents for zein but may contribute t o the solvent power of primary solvents in binary systems; and diluents, which have no solvent power for zein and are not capable of contributing to the solvent power of primary solvents when used in binary or more complex mixtures. Primary organic solvents for zein are either acids, amides, amineb, or hydroxides, although not a11 compounds of these types are zein solvents (2). Propylene glycol is a good zein solvent at room temperature, but ethyl alcohol and glycerol are primary solvents only when heated t o elevated temperattures (7, 8 ) , and 1
Present address, General Milla h a . , Minneapolia, Minn.
Northern Regional Research Laboratory, U. S. Department of Agriculture, Peoria, 111.
amyl alcohol and sorbitol will not peptize zein a t any temperature. Likewise, water is not a primary solvent for zein, possibly because it denatures the protein at temperatures below those required to peptize it. The authors classified secondary solvents for zein (6) as activehydrogen compounds and showed that there is a positive correlation between the effectiveness of certain of these compounds 3 s zein solvents and their capacity to act as electron acceptors in forming hydrogen bridges. Chloroform, nitromethane, formaldehyde, and acetoacetic ester are good solvents of this type. Somewhat anomalousIy, because their hydrogens are so weakly active, benzene, toluene, and similar aromatic compounds are also secondary zein solvents. Compounds which do not contain the carboxyl, amido, amino, or hydroxyl group necessary to form primary solvents, and d o not contain any sufficiently active hydrogen to make them act as secondary solvents, may be classed as diluents. Hexane, diethyl ether, and ethyl acetate are representatives of this group. While the classification of ternary organic solvent systems for zein seems simple and clearly defined from the above outline, it is considerably more complicated. As previously indicated, the line of demarcation between primary solvents and nonsolvents is not sharp, as illustrated by the wide differences in solvent powers of propylene glycol, glycerol, and sorbitol. Likewise, the dividing line between primary solvents and secondary solvents is indefinite. Zein denatures so rapidly in water at elevated temperatures that water must be considered a nonsolvent despite its being a hydroxide. Water, however, has sufficiently active hydrogen to make i t an excellent secondary solvent. A mixture of 75% ethyl alcohol and 25y0 water is a good zein solvent at temperatures above 0” C.; the alcohol alone must be heated to 120’ C. or higher t o peptize the protein, To complicate the picture further, acetone, which is not a primary solvent at any temperature and is a fair secondary solvent when used with the lower aliphatic alcohols, is a good solvent in binary mixtures with water. Furthermore, the borderline between compounds which have sufficiently active hydrogen t o make them secondary solvents and thwe which are simply diluents is not sharply defined. Dichloropentane is a. little better than hexane as a diluent, whereas 2,2,4-trichloroethane is a very good secondary solvent.
Figure 1.
Trilinear Diagrams for Critical Pepttmtion Temperatures
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INDUSTRIAL AND ENGINEERING CHEMISTRY METHYL PCETATE x BY wr.
ETHYL ALGOUOL
zmw
WPlTER
WATER
xBlw
ETWL PLCOHOL
%arm.
Vol. 36, No. 5 TOLUENE
METWL OELLOSOLVE a BY WT
ETHYL eLconoL a BY WT
METHYL CELLOSOLVE fWWT
Figure 2. Trilinear Diagrams for Critical Peptization Temperatures
I N RECENT years numerous patents have been issued on the subject of complex zein solvents. Hansen (6) found that triethanolamine may be added to alcohol-water solvent systems for zein to improve the transparency of fdms formed from such mixtures. He also described the use of leveling solvents such as tert-butyl alcohol and ethylene glycol monomethyl ether for use with aqueous alcohol solutions of zein to keep the protein from precipitating during the unequal evaporation of the water and lower alcohol from the films; he also proposed a large number of high-boiling alcohols, amides, and amines as components of zein solvents because of their plasticizing value. Sturken (9) was granted a patent covering the use of acetic acid as a stabilizing agent in zein-glue dispersions in aqueous alcohol and formaldehyde, Veatch (ii) patented the use of benzene and of benzenetoluene mixtures as components of solvent systems for zein to improve their compatibility with waxes. Coleman (1) was granted numerous patents covering binary and ternary solvent systems for zein. The authors (3)previously reported the use of aldehydes as gelation inhibitors in aqueous alcoholic zein dispersions. The first seven trilinear diagrams of Figure 1 indicate the wide range of alcohol-water-acetaldehyde and alcohol-water-butyraldehyde mixtures and the somewhat smaller range of alcohol-waterformaldehyde mixture, which can be used to produce good zein solvents. The dotted lines in the three alcohol-water-formaldehyde diagrams show that the addition of formaldehyde is limited because the aqueous solution used (commercial formalin) contains only 37% of the gas. Ternary solvent systems for zein composed of acetone, water, and formaldehyde are similar in solvent characteristics t o the ethyl dcohol-water-formaldehyde mixtures, but are distinctly superior in their resistance t o gelation. Acetone-water systems containing as little as 5% formaldehyde are markedly resistant t o gelation, wheress zein dispersions in ethyl aloohol and water
containing low concentrations of formaldehyde gel readily, unless the water content is kept below 5-100/o. The addition of rosin or shellac to binary solvents, such as alcohol and water, substantially lowers the critical peptization temperatures of zein in these mixtures. The presence of rosin in such systems greatly reduces the tendency of the protein dispersion t o set to an irreversible gel. The trilinear critical peptization temperature diagrams (Figures 1 and 2), prepared in the manner previously described @), illustrate the foregoing generalizations relative to ternary solvent, systems for zein and suggest the wide range of compositions available for commercial purposes. Each system was thoroughly investigated throughout the range of zein solubility, and the critical peptization temperatures were determined for a series of particular solvent compositions covering this entire area. After the individual peptization temperatures were determined, lines were drawn connecting like temperatures to give the contour isotherm lines shown in the linear graphs. LITERATURE CITED
(1) Coleman, Roy E.,U. S. Patents 2,185,110-26(1939). (2) Evans, C.D.,and Manley, R. H., IND.ENG.CHBM.,33, 1416 (1941). (3)Ibid., 35, 230-2 (1943). (4) Galeotti, G., and Giampalmo, G., 2. Chem. Znd. Kolloids, 3, 118-26 (1908). (5) Hansen, D.W.,U. 9.Patents 2,074,332and 2,102,623(1937); 2,115,716-17 (1938). (6) Manley, R.H., and Evans, C. D., IND.ENQ.C E ~ M 35, . , 661-5 (1943). (7) Manley, R. H.,and Evans, C. D., J. Biol. Chem., 143, 701-2 (1942). (8) Osborne, T.B., J . Am. Chem. Soc., 19,525-32 (1897). (9) Sturken, Oswald, U. 8. Patent 2,115,240(1938). (10) Swallen, L. C.,IND. ENQ.CEEM.,33, 394-8 (1941). (11) Veatch, Collins, Zbid., 2,134,769 (1938).
