Conversion/degradation of isoflavones and color alterations during the drying of okara

The aim of this work was to investigate the convective drying of okara, a by-product from soymilk processing. The specific objectives were as follows: to model the drying kinetics using the Fick and Page models; and to evaluate the color and isoflavone content during drying. An oven-dryer with hot air circulation at 50, 60 and 70 degrees C was used. Samples were taken at each predetermined time to analyze the isoflavone profile by UHPLC and the color. The Page model fitted the drying kinetics data well. Throughout drying, there was a decrease in the color parameters (lightness and hue angle), showing sample browning. A significant reduction in the isoflavone content was observed at 70 degrees C, possibly due to thermal degradation. During the initial stage of drying at 50 degrees C, daidzin and genistin were converted to the aglycones daidzein and genistein, respectively, probably due to residual beta-glucosidase activity. However, isoflavone degradation was observed during the final stages of drying at 50 degrees C. (C) 2016 Elsevier Ltd. All rights reserved.