Abstract:

In this paper, response surface methodology was used to optimize the composition of AST-based culture medium
for Streptococcus sojalactis SY1.1 to obtain high density of bacteria. Through single-factor experiments, the optimum carbon
source and nitrogen source were found to be sucrose and soy peptone, respectively. The major medium components for
SY1.1 were screened by Plackett-Burman design. Then, the optimum culture medium was determined to consist of 10 g/L
sucrose, 20 g/L soy peptone, 2 g/L dipotassium phosphate, 85.8 mL/L tomato juice, 109 mL/L carrot juice and 6 g/L corn
steep liquor at pH 6.8 by central composite design and response surface analysis. The cell production of SY1.1 cultured in the
optimized medium for 12 h at 37 ℃ was (8.9±0.2) ×108 CFU/mL, which was 8.64 times higher than that (1.03×108 CFU/mL)
observed with soymilk as initial medium.

Key words: Streptococcus sojalactis, optimum culture medium, Plackett-Burman, response surface optimization