Characteristics of L-lactic acid production by Rhizopus oryzae mutant RL6041

A high-yield mutant strain Rhizopus oryzae RL6041 induced by ions implantation was used in the present study. L (+)-lactic acid was generated by RL6041 grown on liquefied corn starch as a substrate. With optimal conditions (Liquefied corn starch 150g/L, (NH4)(2)SO4 2.0g/L, MgSO4 center dot 7H(2)O 1.0g/L, ZnSO4 center dot 7H(2)O2g/L, KH2PO4 0.2g/L, CaCO3 8%, medium size 20/250Ml, seed age 6h, fermentation temperature 38 C), the yield of L (+)-lactic acid in shake-flask reached 133 similar to 136g/L after 36h, indicating that the conversion rate was as high as 88%similar to 91%, and the productivity was 3.75g/L(.)h. There was almost a 70% increase in lactic acid production compared with the original strain RE3303.