Water-Soluble Zein by Enzymatic Modification in Organic Solvents' (1993)

Cereal Chem. 70(2): 115-121 Water-soluble zein was produced using a dual-phase, sequential enzy- modified zein to 99% for enzyme-modified and ultrafiltered zein. At less matic modification and ultrafiltration. Zein was first partially hydrolyzed than DH20, solubility was also a function of pH and membrane pore in an organic solvent by a protease, followed by an aqueous phase size. Foaming properties were affected by DH, membrane pore size, and hydrolysis with the same protease. Ultrafiltration of the reaction mixture pH of measurement. At a water activity of 0.97, moisture sorption was with a 10,000 and/ or a 30,000 molecular weight cut-off membrane yielded 2.6 g of water per gram of solids for the enzyme-modified and ultrafiltered fractions with an average of 5,400 Da. A significant improvement in hydrolysates, compared to less than 0.25 g of water per gram of solids certain functional properties of zein was observed, controlled largely by for unmodified zein. the degree of hydrolysis (DH). Solubility increased from 0% for the unToday's formulated food products require cost-effective proteins with specific functional properties. Functional properties of proteins are those physicochemical attributes that lend desirable physical characteristics to a food and are responsible, in part, for certain textural and sensory properties of those foods. These functional properties include solubility, water and fat absorption, gelation, emulsion stability, whippability, and foaming and sensory properties (Kinsella 1976). Compared to soy protein, corn has received little attention from the food industry as a potential food ingredient. No commercial corn concentrates or isolates exist, with the exception of zein produced in low quantities for very specialized applications (P. Freeman, personal communication). This may change in the near future, however. Large amounts of proteinaceous by-products are produced by corn refiners in the form of corn gluten meal (CGM, 69% db) and corn gluten feed (CGF, 24.5% protein. db). These are primarily by-products of the manufacture of starch-based industrial products (e.g., fructose, dextrose, ethanol, etc.). The increasing volume of these industrial products results in a simultaneous increase in the by-products. Indeed, the viability of the corn ethanol industry relies heavily on the profits from the sale and marketing of the nonstarch products (protein, oil, and fiber). Thus, there is a need to find alternate uses for the nonstarch products that will yield a better return than animal feed does. Zein is a storage located in protein bodies 1-2 ,.m in diameter (Wilson 1987, Abe 1989). In contrast to the albumins and globulins, zein has a high concentration of nonpolar amino acids such as leucine, isoleucine, valine, alanine, proline, and glutamine, rendering it soluble primarily in alcoholic solvents. Poor water solubility is a hindrance to the utilization of corn proteins as a food ingredient. Solubility in water is a key functional property because proteins generally have to be in a solution or in a fine suspension to exert other desirable properties (Kinsella 1976). This article reports our studies on the enzymatic modification of zein, and the subsequent fractionation of the hydrolysis products by ultrafiltration, specifically for producing water-soluble zein. Enzyme hydrolysis was selected rather than chemical treatments because of milder process conditions, higher specificity, easier control of the reaction, and minimal formation of toxic by-products. Casella and Whitaker (1990) hydrolyzed zein using trypsin but obtained a very low degree of hydrolysis because the reaction was conducted in an aqueous environment. We have substantially improved the process by conducting the initial en