β-Glucosidase activity was measured as follows: 50 μL of diluted enzyme solution (10−3 –10−5 in 0.1 M sodium acetate buffer, pH 4.5) and 50 μL of 7.5 mM 4-nitrophenyl-β-D-glucopyranoside (Sigma-Aldrich Japan, Japan) were mixed and incubated at 40°C for 30 min