Abstract:

In order to improve the yield of L-malic acid, the fermentation process and glucose metabolism pathways for
Rhizopus oryzae mutant strain CICC40503-JST were preliminary studied in this paper. The culture medium and fermentation
conditions were optimized by using combination of single factor method and response surface methodology with central
composite design. Meanwhile, the production and possible metabolic pathway of L- malic acid were explored using
stirred tank fermentor. The results showed that the optimal medium composition for malate production were determined
as follows: glucose, (NH4)2SO4, MgSO4, FeSO4·7H2O, KH2PO4, ZnSO4 and CaCO3 100, 4.0, 0.3, 0.025, 0.5, 0.1 and
80 g/L, respectively. The fermentation conditions were optimized to be spore suspension incubation for 48 h and subsequent
fermentation in a Sartorius fermentor at 32 ℃ for 48 h followed by another 24 h after addition of fresh culture medium with
a ventilation rate of volume of 0.20 L/(min·L) and a rotation rate of 500 r/min. Under these conditions, the yield of L-malic
acid was 57.71 g/L. In conclusion, the yield of malate could be improved significantly through effective utilization of glucose
under the optimized culture conditions.

Key words: Rhizopus oryzae, glucose, L-malic acid, central composite design, enzyme activity