Optimization of antimicrobial substances produced from Lactobacillus paracasei subsp. paracasei NTU 101 (DSM 28047) and Lactobacillus plantarum NTU 102 by response surface methodology.

Response surface methodology (RSM) was used to study the effects of medium composition and growth conditions on antimicrobial substances produced by Lactobacillus paracasei subsp. paracasei NTU 101 and Lactobacillus plantarum NTU 102. These strains are used in the food and pharmaceutical industries because of their beneficial effects on the human gastrointestinal tract and in immune modulation. The production of antimicrobial substances was optimized by the Box-Behnken experimental design. An empirical model was developed through RSM to describe the relationship between variables (molasses, soymilk, and incubation temperature). The maximum antimicrobial activity of L. paracasei subsp. paracasei NTU 101 was 12.50 AU/mL with 18.33 g/L molasses and 14.53 g/L soymilk at a temperature of 35.00 °C, whereas in MRS (de Man, Rogosa, and Sharpe) broth, the activity was 14.00 AU/mL. Similarly, the maximum antimicrobial activity of L. plantarum NTU 102 was 15.00 AU/mL with 20.56 g/L molasses and 13.54 g/L soymilk at a temperature of 36.50 °C, whereas in MRS, the activity was 13.50 AU/mL. The antimicrobial activities visualized in response surface plots were 12.26 and 15.59 AU/mL for NTU 101 and 102, respectively. The results derived from RSM regression were close to those obtained with the experimental design treatments. These results revealed that an alternative medium could be used for large-scale commercial production of the antimicrobial substances, with potential prospects for application.