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Optimizing Extraction of Zein and Glutelin-Rich Fraction During Sequential Extraction Processing of Corn

¹Department of Food Science & Human Nutrition, Center for Crops Utilization Research, Iowa State University, Ames, IA 50011. ²Presently, Research Chemist, National Center for Agricultural Utilization Research, 1815 N. University St., Peoria, IL 61604. ³Corresponding author. E-mail: ljohnson@iastate.edu. Phone: 515-294-4365. Fax: 515-294-6261.

This study was conducted to improve yields and qualities of corn protein co-products produced by the sequential extraction process (SEP), a process using ethanol to fractionate corn in producing fuel ethanol. A two-stage extraction protocol was evaluated to recover zein and subsequently recover a glutelin-rich fraction (GRF). After the simultaneous oil-extraction and ethanol-drying step of SEP, zein was extracted from the anhydrous-ethanol-defatted, flaked corn by using 70% (v/v) ethanol at 60°C for 1.5 hr in a shaking water bath. Zein was recovered by ultrafiltering and then drying in a vacuum-oven. Zein yield was 65% of the available zein in the flaked corn. SDS-PAGE band patterns of the recovered zein closely resembled that of commercial zein. After zein extraction, the GRF was extracted using 45% ethanol and 55% 0.1M NaOH at 55°C for 2 hr. The extract was concentrated by ultrafiltration and then freeze-dried. GRF yield was ≈65% of the available protein. Freeze-dried GRF contained 90% crude protein (db), which classified the protein as a protein isolate. As with the protein concentrate from the original SEP, the GRF isolate was highly soluble in water at pH ≥ 7, had good emulsifying and foaming properties, formed stable emulsions, and was heat-stable.