Abstract: The medium composition and culture conditions for L-lactic acid production via the co-fermentation of glucose and xylose with Rhizopus oryzae were optimized by response surface methodology. A 7-factor, 3-level central composite design was performed based on single factor experiments and the quadratic regression analysis of the experimental results was conducted by using Design Expert software. The optimum medium composition (g/L) was glucose 100, xylose 50, (NH4)2SO4 3.0 and KH2PO4 0.3, and the optimum culture conditions were medium volume in a 250 mL flask of 50 mL, shaking table speed of 180 r/min, inoculation amount of 12% and culture temperature of 32 ℃. Under these conditions, the concentration of L-lactic acid reached up to 119.216 g/L after 72 h fermentation and the conversion rate was up to 79.48%.

Key words: glucose, xylose, L-lactic acid, response surface method, optimization