Effect of Moisture Content on the Quality of Soybean Oil and Meal Extracted by Isopropyl Alcohol and Hexane

Soyflakes and soybrokens having 8% to 16% wet basis (w.b.) moisture contents were extracted for 8 h (about 50% extraction) using the azeotrope (91%) of isopropyl alcohol (IPA) at 7.75 ml/min flow rate. The moisture contents of soyflakes and soybrokens significantly affected oil recovery with IPA. Regression analysis was performed to optimize moisture contents of soyflakes and soybrokens during IPA extraction. The optimum moisture content was found to be 13.4% and 12.6% (w.b.) for soyflakes and soybrokens, respectively. Qualities of IPA-extracted oil [color and free fatty acid (FFA) content] and of de-oiled soy meal (whiteness value and crude protein content) were determined and compared with those of absolute n-hexane-extracted oil and meal at 4.15, 6.35, and 7.15 ml/min flow rates. Prior to the IPA and n-hexane extractions, soyflakes and soybrokens were hydrated to the optimum moisture content. The colors of IPA-extracted oil and soymeal were somewhat darker than those extracted by n-hexane. IPA-extracted oil had significantly lower FFA content than the n-hexane-extracted oil. De-oiled soy meals obtained from IPA extraction had lower whiteness values indicating darker color compared to n-hexane. Crude protein contents were similar in both oil and meal obtained from both solvent extraction processes.