Recovery of isoflavone aglycones from soy whey wastewater using foam fractionation and acidic hydrolysis.

The purpose of this work was to recover isoflavone aglycones from industrial soy whey wastewater, where the isoflavone aglycones mainly existed in the form of β-glycosides. First, foam fractionation was used for effectively concentrating the total soy isoflavones, including isoflavone aglycones and β-glycosides, from the wastewater. Fourier transform infrared spectroscopy indicated the existence of complexes of soy isoflavones and soy proteins. When soy proteins were used as the collectors, a high enrichment ratio of 3.68 was obtained under the optimal operating conditions of temperature of 50 °C, pH of 5.0, volumetric air flow rate of 100 mL/min, and loading liquid height of 400 mm. Subsequently, acidic hydrolysis was used for hydrolyzing β-glycosides in the foamate into aglycones. Using response surface methodology, a hydrolytic percentage could reach 96% under the optimum hydrolysis conditions of hydrolytic temperature of 80 °C, hydrochloric acid concentration of 1.37 mol/L, and hydrolytic time of 90 min.