Supercritical carbon dioxide processing of soybean isoflavones and utilization of partially defatted soybean cake in soymilk

This study investigated ethanol–water co-solvents for supercritical carbon dioxide extraction of soybean isoflavones and the use of partially defatted soybean cake in soymilk. Tainan Selected No. 1 yellow soybean and Tainan No. 5 black soybean were extracted with 60–40 or 80–20% ethanol–water. Fractions were collected at 20.7, 17.2, 13.8, and 10.3 MPa, and five isoflavones were quantified by HPLC. Among the conditions tested, Tainan Selected No. 1 yellow soybean extracted with 80% aqueous ethanol showed the highest sum of quantified isoflavones (13.47–14.77 mg/g dry matter). Daidzin, glycitin, genistin, daidzein, and genistein were approximately 2.97–3.11, 0.55–0.58, 3.63–3.81, 6.27–6.63, and 0.06–0.07 mg/g dry matter, respectively. Black soybean showed slightly higher summed isoflavone contents with 60% than with 80% aqueous ethanol. Sequential pressure fractionation produced only limited differences among fractions. Partially defatted soybean cake was reincorporated into soymilk at 0, 3, and 5%. Soybean cake addition increased dietary fiber and selected functional components, while all formulations achieved overall acceptability scores above 5.0. Under the conditions evaluated, ethanol’s effect on the isoflavone contents of the collected fractions varied by soybean cultivar.