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Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/15/2003 Publication Date: 7/1/2003 Citation: HOJILLAEVANGELIST, M.P., JOHNSON, L.A. OPTIMIZING EXTRACTION OF ZEIN AND GLUTEILIN RICH FRACTION DURING IN SEQUENTIAL EXTRACTION PROCESSING OF CORN. CEREAL CHEMISTRY. 2003. Interpretive Summary: The Sequential Extraction Process (SEP) is an alternative method to produce ethanol from corn. SEP uses this ethanol to also extract oil and proteins from the corn. The corn proteins recovered are zein, which is extracted with the oil, and the alkali-soluble glutelins. Both proteins have properties that are desirable for food and non-food applications. The presence of zein in the extracted oil complicates the separation processes in SEP. The amount of zein removed with the oil must be reduced further or eliminated altogether to make SEP more efficient. We modified SEP's protein extraction phase by first removing the zein using 70% aqueous ethanol and then extracting the glutelin-rich fraction (GRF) as before by using a mixture of ethanol and dilute alkali. This two-stage extraction method maximized the yields of both proteins. The GRF, after it was recovered in solid form, had very high protein purity (90% protein content). The GRF was also soluble in water, heat-stable and formed good foams and emulsions - properties that are desirable in many food applications. When these modified protein extraction steps are incorporated in SEP, the process will be able to more efficiently produce proteins with novel qualities, in addition to being a more cost-effective way to produce ethanol. Technical Abstract: This study was conducted to improve the yields and qualities of corn protein co-products produced by the Sequential Extraction Process (SEP), a process using ethanol to fractionate corn. A two-stage extraction protocol was evaluated for recovering zein and subsequently recovering a glutelin-rich fraction (GRF). After the simultaneous oil-extraction/ethanol-drying step of SEP, zein was extracted from the anhydrous-ethanol-defatted, flaked corn by using 70% (v/v) ethanol at 60 degrees C for 1.5 h in a shaking water bath. Zein was recovered by ultrafiltering and then vacuum-oven drying. Yield was 65% of the available zein the flaked corn. SDS-PAGE band patterns of the recovered zein closely resembled that of commercial zein. After zein extraction, the GRF was extracted by using 45% ethanol:55% 0.1 NaOH at 55 degrees C for 2 h. The extract was concentrated by ultrafiltration and then freeze dried. GRF yield was about 65% of the available protein. The freeze-dried GRF contained 90% crude protein (db), which classified the product as a protein isolate. As with the protein concentrate from the original SEP, the GRF isolate was highly soluble in water at pH less than 7, had good emulsifying and foaming properties, formed stable emulsions, and was heat-stable. |
