Optimization of culture conditions for the production of antimicrobial substances by probiotic Lactobacillus paracasei subsp. Tolerans FX-6

There is an increasing demand from consumers for natural antimicrobial substances that can be used for food preservation. This study is focused on establishing the conditions to enhance the production of antimicrobial substances by the probiotic Lactobacillus paracasei Subsp. Tolerans FX-6 from Tibetan kefir. The culture conditions were optimized by using response surface methodology, and remarkably the optimized conditions increased the antimicrobial activity by more than 80%. Further characterization revealed that the antimicrobial substances exhibited a broad spectrum of antimicrobial activity against a variety of Gram-positive and Gram-negative bacteria and fungi. Moreover, the antimicrobial substances were highly tolerant to heat and enzyme treatment. Excitingly, the antimicrobial substances were fractionated by HPLC and the sub-fractions generated showed stronger antimicrobial activity than nisin, a highly effective bacteriocin currently used as a food preservative. Overall, these results demonstrate a novel approach to produce effective antimicrobial substances for use as natural preservatives in food.