Optimization of Ginsenosides Hydrolyzing β-Glucosidase Production from Aspergillus niger Using Response Surface Methodology

Abstract

To optimize ginsenosides hydrolyzing β-glucosidase production from Aspergillus niger, 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, CaCl₂, ginsenosides, KH₂PO₄, MgSO₄, polyethylene glycol (PEG), medium volume, inoculum size, and stirring speed), it was found that wheat bran, KH₂PO₄, and stirring speed had significant effect on β-glucosidase activity due to very low p-values (p<0.05). Subsequently, wheat bran, KH₂PO₄, 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; KH₂PO₄, 1.78 g/l; stirring speed, 161.60 rpm/min). Finally, under optimal fermentation conditions, ginsenoside Rb₁ was converted to Rd and F₂ by A. niger within 10 min. Little compound K was detected at 30 min, and finally F₂ was completely transformed to compound K within 8 h. The putative conversion pathway of Rb₁ by A. niger was Rb₁, Rd, F₂, and compound K.