Subcritical water enhances hydrolytic conversions of isoflavones and recovery of phenolic antioxidants from soybean byproducts (okara)

This study aimed to enhance the hydrolytic conversions of conjugated isoflavones to non-conjugated aglycones from soybean byproducts (okara) using subcritical water hydrolysis. Processing parameters for temperature, pressure and solid liquid mixing ratio were set as constant variables following the experimental design performed in our previous study for the optimization of isoflavones extraction and kinetics modeling using subcritical water and response surface methododology. Fixed operating conditions were temperature (T: 150 degrees C), pressure (P: 4 MPa) and solid liquid ratio (s/l: 20 mg/mL), and the reaction time was the sole control variable. The results revealed that prolonging the reaction time increased the concentrations of genistein and daidzein by 6.5 and 9 fold, respectively. Total phenolic contents increased up to 55%, and the antioxidant activities exhibited a strong correlation with isoflavone aglycones and phenolic contents. (C) 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.