Enhanced β-Glucosidase Activity of Lactobacillus plantarum by a Strategic Ultrasound Treatment for Biotransformation of Isoflavones in Okara

The enhanced β-glucosidase of Lactobacillus plantarum BCRC 10357 was investigated by a strategic ultrasound treatment on bacteria at different growth stages to induce biological stress response for biotransformation of isoflavones from glucosides to aglycones in okara. Without ultrasound, the highest β-glucosidase activity was occurred in 12-h incubation as 24.45 U/mL; while after ultrasound treatment at death phase, the highest β-glucosidase activity was greatly enhanced to 48.80 U/mL in 24-h re-incubation, showing the bacteria at early death phase behaving the highest resistance to stress than at other stages. With strategically ultrasound-treated L. plantarum BCRC 10357 to ferment okara in the broth at 37 °C, the fraction of bioactive aglycones (daidzein and genistein) in isoflavones was increased from 57% in 12 h to 89% in 36 h. The effective method to improve β-glucosidase released from L. plantarum was developed for the valorization of okara as potential functional ingredients in food.