Corn protein & oil recovery after germ wet milling
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Copyright (2014) by the American Society of Agricultural & Biological Engineers All rights reserved. Germ wet milling is a recently proposed aqueous processing method designed to increase germ protein and oil concentration by water soaking and wet fractionation of dry-milled corn germ. Corn protein concentrate was prepared after aqueous processing of dry milled germ using membrane filtration or isoelectric precipitation. The amount of protein recovered was a function of the protein dispersibility index of the starting material, which depends on soak temperature and time. Extracts prepared after germ wet milling contained 59-65% (dmb) protein while concentrates had 65-82% protein. The technique used for protein recovery also influenced the mass and protein yield and composition. For all treatments, membrane filtration was a more effective method than isoelectric precipitation for recovering protein from extract. A separate method, aqueous enzymatic oil extraction (AEOE), was used to evaluate the oil recovery potential after germ wet milling. AEOE provides an opportunity to design an environmentally friendly and integrated process for protein and oil fractionation to reduce costs of bioenergy production. The effect of enzyme dosages and/or elimination of the acidic protease on oil extraction from high protein, high PDI (protein dispersibility index) corn germ and high protein, low PDI corn germ were evaluated. AEOE using a combination of cellulases and xylanase (Optimash XL), an acidic protease (Fermgen), and a basic protease (Protex P) resulted in oil recoveries as high as 72% of the initial oil content. A two-fold reduction in enzyme dosages was possible with little or no effect on oil recoveries for both types of germ.
