초록
<P>To optimize ginsenosides hydrolyzing β-glucosidase production from <I>Aspergillus niger</I>, response surface methodology was carried out in two stages. The Plackett–Burman design was achieved to screen the important variables that influence β-glucosidase production. Among 10 variables (wheat bran, soybean powder, CaCl<SUB>2</SUB>, ginsenosides, KH<SUB>2</SUB>PO<SUB>4</SUB>, MgSO<SUB>4</SUB>, polyethylene glycol (PEG), medium volume, inoculum size, and stirring speed), it was found that wheat bran, KH<SUB>2</SUB>PO<SUB>4</SUB>, and stirring speed had significant effect on β-glucosidase activity due to very low <I>p</I>-values (<I>p</I><0.05). Subsequently, wheat bran, KH<SUB>2</SUB>PO<SUB>4</SUB>, and stirring speed were further optimized using central composite design. The optimal β-glucosidase production was predicted to be 4650.14 U/ml with the combination of factors (wheat bran, 34.51 g/l; KH<SUB>2</SUB>PO<SUB>4</SUB>, 1.78 g/l; stirring speed, 161.60 rpm/min). Finally, under optimal fermentation conditions, ginsenoside Rb<SUB>1</SUB> was converted to Rd and F<SUB>2</SUB> by <I>A. niger</I> within 10 min. Little compound K was detected at 30 min, and finally F<SUB>2</SUB> was completely transformed to compound K within 8 h. The putative conversion pathway of Rb<SUB>1</SUB> by <I>A. niger</I> was Rb<SUB>1</SUB>, Rd, F<SUB>2</SUB>, and compound K.</P>