Application of response surface methodology (RSM) for optimization of high-yielding L-lactic acid strains selected by low-energy ion implantation

Li Shichang, Zhu Zhaoyang, Gu

Abstract

In this paper, in order to obtain mutant strains with high yield of L-lactic acid, the original strain Lactobacillus casei SB-310 was implanted by nitrogen ions. It was found that the higher positive mutation rate was appeared when the output power was 10keV and the dose of nitrogen ion implantation was 50×2.6×1013 ions/cm2. A mutant strain which was named as Lactobacillus casei NE-19 was screened, its yield of L-lactic acid was about 120 g/L, and it was high increasing compared to the original strain (80.3 g/L). Response surface method was applied to optimize the fermentation medium. The highest yield of L-lactic acid was obtained when the concentration of glucose, peptone, beef extract and yeast extract were 153.68 g/L, 17.27 g/L, 15.89 g/L and 8.28 g/L respectively, and the highest yield was 134.79 g/L.