Aqueous Fractionation of Dry-Milled Corn Germ for Food Protein Production
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To improve economics, dry-grind corn ethanol plants are transitioning to fractionation processes to produce higher value coproducts from non-fermentable fractions. Dry-milled corn germ, which contains a significant amount of non-fermentable components (protein, oil, and fiber), is a potential source of higher value food protein. However, the relatively low protein concentration in dry-milled germ currently hinders its use as a starting material for the production of germ protein extracts and concentrates. Germ wet milling is a recently proposed method designed to increase germ protein and oil concentration by water soaking and wet fractionation of dry-milled germ. In this study, the effect of soaking conditions (pH, temperature, time) on germ composition was determined to identify the best conditions for producing germ with high protein content and high protein dispersibility index. The soaking and subsequent processing of dry-milled germ increased protein content from 15 to 21 %, reduced starch from 33 to 9 %, and increased oil content from 16 to 39 %. The effect of soaking and subsequent processing conditions on germ protein quality was also evaluated to determine the suitability of using the defatted germ as the starting material for protein concentrate. Soaking dry-milled germ at 25 C at either pH 6.0 or pH 9.0 maintained the protein dispersibility index but soaking at pH 3.0 and/or at a higher temperature were detrimental. Results indicated that the yield of corn protein concentrate prepared by isoelectric precipitation from defatted germ flour was significantly affected by the protein dispersibility index.
