(309a) Optimization of Protein Recovery From Enzyme-Assisted Aqueous Extraction of Soybean Oil

Enzyme-assisted aqueous extraction processing (EAEP) of soybean is an interesting green alternative to hexane extraction processing because of potential revenues from a high-value-added protein co-product. A potentially economically viable aqueous extraction process has been developed at the Center for Crops Utilization Research at Iowa State University using proteases to release oil and protein from extruded soy. Traditional protein concentration and purification methods such as pH precipitation and ultrafiltration are complicated not only by the increased solubility and small molecular weight of hydrolyzed polypeptides, but also by the presence of emulsified oil in the skim fraction. While ultrafiltration has been successful in achieving high quality and high purity protein ingredients, the hydrolysis in this case necessitates the use of low molecular weight cut-off membranes to reduce protein losses, resulting in low fluxes and increased processing costs. To improve the value of the protein fraction from EAEP, experiments were conducted to remove emulsified oil, optimize ultrafiltration flux, and increase protein purity. Centrifugation and membrane filtration methods were investigated to remove emulsified oil. Ultrafiltration conditions investigated include transmembrane pressure, cross flow rate, and the introduction of solids via isoelectric precipitation. Additional enzymatic treatments were utilized to increase protein purity, including alpha-galactosidase to hydrolyze oligosaccharides to monomeric sugars, and phytase to determine the presence of, and if necessary eliminate, phytate-protein-mineral complexes.

Cation exchange chromatography was evaluated for additional protein recovery from both the supernatant from isolelectric precipitation and the permeate from ultrafiltration. Fractions were analyzed for two other potential products - isoflavones and angiotensin-I converting enzyme inhibitor.