Journal of Pure and Applied MicrobiologyVol. 8 No. May 2014 Special Edition

Effect of MgSO4 on Lactic Acid Production in Rhizopus oryzae Fermentation

Chunmei Ge*, Renrui Pan, Jie Zhang, Jingmin Cai and Zengliang Yu

Department of Biological and Environmental Engineering, Hefei University, Hefei, China.

Received on 28 March 2014 and accepted on 03 May 2014

 

ABSTRACT

We investigated the effects of MgSO4 on L-lactic acid production by the Rhizopus oryzae strain RLC41-6 in order to improve the production rate and quality of L-lactic acid. We also studied the effects of MgSO4 on intracellular lactate dehydrogenase (LDH) and alcohol dehydrogenase (ADH) activity. Different concentrations of MgSO4 were added to the fermentation medium before culture of R. oryzae at 36?C for 36 h. L-lactic acid concentration was determined by reverse phase high performance liquid chromatography, and the activity and intracellular expression of LDH and ADH were examined via polyacrylamide gel electrophoresis and kinetic methods. Although increasing MgSO4 concentrations led to increased lactic acid production by R. oryzae, MgSO4 had no effect on LDH expression or activity. Furthermore, MgSO4 promoted mycelium growth and inhibited ADH activity. With an initial MgSO4 concentration of 0.075%, maximum mycelium production of 36.8 g/L was achieved and L-lactic acid was the only fermentation product, at ~138 g/L with a 92% conversion rate. An appropriate concentration of MgSO4 can inhibit the conversion of pyruvic acid into malic acid and fumaric acid as well as both ADH activity and alcohol synthesis, thereby enhancing the conversion of glucose into lactic acid in R. oryzae.

Keywords : L-lactic acid; Rhizopus oryzae; Lactate dehydrogenase; Alcohol dehydrogenase; MgSO4.