Extraction and solubility characteristics of zein proteins from dry-milledcorn

Zein isolation by aqueous ethanol extraction from dry-milled corn produces a mixture of zeins, covalently linked polymers (dimers, tetramers, etc.) an d higher-molecular-weight aggregates, some of which were not soluble in aqu eous alcohol. The insoluble particles were identified as protein aggregates which form when the extraction solution is heated, particularly under alka line conditions. The insoluble protein aggregates were not present in zein isolated by the same method from corn gluten meal. Zeins extracted from cor n gluten meal and dry-milled corn were fractionated (by differential solubi lity) to identify differences in their polypeptide compositions. Using poly acrylamide gel electrophoresis, beta- and gamma -zeins were detected in dry -milled corn, but only trace amounts of beta -zein were found in corn glute n meal. Treatment of dry-milled corn with 0.55% lactic acid and 0.2% sulfur dioxide at 50 degreesC for 6 h before ethanol extraction resulted in a 50% increase in zein isolate yield with high solubility (98%). This pre-extrac tion treatment cleaved disulfide linkages of the beta- and gamma -zeins and significantly reduced insoluble aggregates in zein isolates.