Abstract: In order to improve the yield of antifungal substances produced by Lactobacillus paracasei （L. paracasei） N22 obtained previously, the response surface method was used to optimize the culture conditions for antifungal substances produced by L. paracasei N22, with Pichia pastoris as the yeast indicator and the size of inhibition zone as the evaluation index. The carbon source and nitrogen source in the MRS culture medium were optimized, and the effects of different levels of culture temperature, initial pH value and fermentation time on yield of antifungal substances produced by L. paracasei N22 were assessed. The results showed that the culture temperature, initial pH value and fermentation time were the main determinative factors. The optimal culture conditions for antifungal substances produced by L. paracasei N22 were determined by using Box-Behnken experiment design and response surface method the culture temperature was 34.16 ℃, the initial pH value was 5.33, and the culture duration was 35.44 h. Under these conditions, the largest diameter of inhibition zone was 16.34 mm, and the desirable rate was 97.90%. After verification, the largest diameter of inhibition zone was 16.58 mm. The culture conditions determined in this study increase the yield of antifungal substances produced by lactic acid bacteria.

Key words: lactic acid bacteria, antifungal substances, response surface method, culture conditions optimization