A recombinant Thermotoga maritima beta-glucosidase A (BglA) was purified to homogeneity for performing enzymatic hydrolysis of isoflavone glycosides from soy flour. The kinetic properties K(m), k(cat), and k(cat)/K(m) of BglA towards isoflavone glycosides, determined using high-performance liquid chromatography, confirmed the higher efficiency of BglA in hydrolyzing malonylglycosides than non-conjugated glycosides (daidzin and genistin). During hydrolysis of soy flour by BglA at 80 degrees C, the isoflavone glycosides (soluble form) were extracted from soy flour (solid state) into the solution (liquid state) in thermal condition and converted to their aglycones (insoluble form), which mostly existed in the pellet to be separated from BglA in the reaction solution. The enzymatic hydrolysis in one-step and two-step approaches yielded 0.38 and 0.35 mg genistein and daidzein per gram of soy flour, respectively. The optimum conditions for conversion of isoflavone aglycones were 100 U per gram of soy flour, substrate concentration 25% (w/v), and incubation time 3 h for 80 degrees C.

To produce aglycone isoflavones from soy flour, the b-glucosidase A gene (bglA) of Thermotoga maritima was overexpressed in Escherichia coli BL21-CodonPlus (DE3)-RIL. The K m and V max values of the purified BglA for pNPG were 0.43 mM and 323.6 U mg -1 , respectively, and those for salicin were 9.0 mM and 183.2 U mg -1 , respectively. The biochemical and kinetic characteristics of his-tagged BglA were found to be similar to those of BglA, except for the temperature stability and specific activity. Production of aglycone isoflavones from soy flour by BglA was examined by HPLC. For 3 h at 80°C, all the isoflavone glycosides approximated to the complete conversion into aglycone isoflavones, over seven times higher than that obtained from soy flour without BglA.