Abstract: Plackett-Burman design was adopted to screen 3 main factors out of 15 ones affecting the activity of β-galactosidase produced by Lactobacillus acidophilus CICC6075. Based on a Box-Behnken design involving 15 experiments of 3 variables at 3 levels, the interactive effects among the screened factors were analyzed by response surface methodology. Results showed that the most significant effects on the fermentation process were contributed by the factors of yeast extract powder, citric acid triamine and fermentation temperature. Their optimal values are determined as follows: temperature 36 ℃, yeast extract powder 6.22 g/L, and citric acid triamine 2.35 g/L. Under these conditions, the maximum enzyme activity reached 3.98 U/L, which was closed to the predicted value of 3.95 U/L and rudely 3 times higher than before optimization.

Key words: Lactobacillus acidophilus, β-galactosidase, response surface methodology, fermentation temperature, citric acid triamine, yeast extract powder