Extraction yield of isoflavones from soybean cake as affected by solvent and supercritical carbon dioxide

Soybean cake has been shown to be a rich source of isoflavone and can be produced during processing of soybean oil as byproduct. The objectives of this study were to compare the extraction yield of isoflavone from soybean cake by solvent and supercritical carbon dioxide, and study the conversion of isoflavone glucosides to the biologically active aglycone by employing β-glucosidase. Results showed that with supercritical carbon dioxide extraction, a maximum yield of malonylglucoside and glucoside was generated at 60 °C and 350 bar, while a high level of acetylglucoside and aglycone was produced at 80 °C and 350 bar. Supercritical carbon dioxide extraction resulted in a lower yield of total isoflavone than solvent extraction, but the former was more applicable to extraction of acetylglucoside and aglycone, and the latter to malonylglucoside and glucoside. A peak level of aglycone was attained from conversion of isoflavone glucoside by β-glucosidase at 55 °C, pH 5, concentration 50 U/ml and incubation time of 2 h.