Bioconversion of ginsenoside Rb1 to ginsenoside Rd by β-glucosidase from Thermus caldophilus

Ginsenoside Rb1 is the most predominant ginsenoside among ginsenosides of Panax species(ginseng). Ginsenoside Rb1 was converted into pharmaceutically active minor ginsenoside Rd by hydrolysing 20-C β-(1 → 6)-glucoside using β -glucosidase from Thermus caldophilus. The enzyme activity to produce ginsenoside Rd was optimal at pH 6.0, 90 ℃, 0.05 units/㎖, and the enzyme was stable below 75 ℃. Under the conditions of pH 6.0, 75 ℃, 0.05 units/㎖, the β-glucosidase produced 0.7 g/l of Rd from 1.1 g/l of Rb1 at reaction time of 100 min, with a product yield of 63.6 %.