One hundred milligrams solid samples (soybean germ), or
500 lL liquid samples (vinegar) were taken, and 1.5 mL of 0.05 M
citrate buffer (pH 4.5) containing 0.1 M NaCl was maintained for
1 h at room temperature. The samples were centrifuged
(12,000g for 5 min), and the supernatant was used as enzyme
source for activity analysis. The b-glucosidase activity was assayed
by a modified procedure, based on the method of Matsuura and
Obata (1993). Two milliliters of the substrate 1 mM p-nitrophenyl-
b-D-glucopyranoside (p-NPG) in phosphate-citrate buffer
(0.1 M pH 5.0) were transferred to a test tube and kept in a water
bath at 30 C for 10 min; then 0.5 mL of the supernatant was added
and the tube left in the water bath at 30 C for 30 min. After incubation
at 37 C for 30 min, the reaction was stopped with 2.5 mL of
0.05 M sodium carbonate. The activity of b-glucosidase was estimated
by reading the absorbance of the liberated p-nitrophenol
at 405 nm. The blank solution was composed of 2.5 mL of 0.05 M
sodium carbonate solution, 2.0 ml of substrate solution and
0.5 mL of 0.05 M citrate buffer (pH 4.5) containing 0.1 M NaCl.
One unit (U) of b-glucosidase activity was defined as the amount
of enzyme required for the hydrolysis of 1 lmol of substrate
(pNPG)/min, under the assay conditions