Abstract: In order to improve the yield of L- malic acid, the fermentation process and glucose metabolism pathways for the Rhizopus oryzae mutant strain CICC40503-JST were preliminary studied in this paper. Optimized the culture medium and fermentation conditions by using single factor experiment and response surface method (Box-Behnken), at the same time, explored the effect of acid production by using stir tank and possible metabolic pathway of L- malic acid. The results showed that the optimal medium compositions for malate production were as follows: glucose, (NH4)2SO4, MgSO4, FeSO4?7H2O, KH2PO4, ZnSO4, CaCO3 were 100 g/L, 4.0 g/L, 0.3 g/L, 0.025 g/L, 0.5 g/L, 0.1 g/L and 80 g/L. The fermentation conditions by means of single factor experiments were found to be as follows: fermentation equipment for stirred tank, a temperature of 32 oC, ventilation volume of 0.20L/min.L, rotation rate of 500 r/min, spore suspension was incubated for 48 hours, carried out fed-batch fermentation after 48 hours during the process, and the fermentation period lasted as long as 72 hours that leading to the L-malic acid yield of 57.71 g/L. In conclusion, by fermentation processing optimization, the yield of malate was raised effectively.

Key words: Rhizopus oryzae, glucose, L-malic acid, Box-Behnken experimental design, enzyme activity