Abstract: The fermentation conditions of lactic acid produced from corn starch by Rhizopus oryzae were investigated. Rhizopus oryzae HB12 was newly isolated from soil samples. Based on single factor and orthogonal tests, the optimal fermentation medium was composed of 140 g/L corn starch, 2 g/L NH4Cl, 0.3 g/L KH2PO4, 0.3 g/L MgSO4·7H2O, 0.05 g/L ZnSO4·7H2O and 80 g/L CaCO3. The optimal fermentation conditions were 2.5 × 106 spores in 50 mL of medium cultured at 35 ℃, 200 r/min shaking for 108 h in 250 mL flask. Under the optimal fermentation conditions, the yield of lactic acid produced from corn starch was up to 104.9 g/L with a conversion of 74.9%. The volumetric production rate was up to 0.97 g/(L·h), which revealed 49.4% enhancement compared with the original conditions. Therefore, Rhizopus oryzae HB12 can effectively utilize inexpensive corn starch for the production of lactic acid, which will have good prospect for industrial application.

Key words: Rhizopus oryzae, lactic acid, fermentation condition, corn starch