Mutation Breeding Of Prime Yielding Strains Of L. Paracasei

Synthesized preservatives are intensively applied in food industry since they can prolong food shelf life. They have, however, side-effects or potential threat to human health. Therefore, the production of nature preservatives from animals and plants as well as microorganisms is a necessity required by development of the society. Due to the production cycle and high cost, nature preservatives are difficult to produce on large scale. The production of bio-preservatives from microorganisms has potential and becomes a hot research subject. Many microorganisms could produce antimicrobial substances, of which lactic acid bacteria (LAB) is the most popular one in research. In this study, bacteriocin which has higher antimicrobial activity and a wide pH range produced by Lactobacillus paracasei HD1.7 was researched. Because the Lactobacillus paracasei HD1.7 is low in production, the study put on mutation breeding on Lactobacillus paracasei HD1.7.In this study, a highly peptide biopreservative producing mutant strain W-6 was obtained from HD1.7 by many mutagenetic treatment with UV, NTG, Microwave. The peptide biopreservative activity of W-6 was from 155AU/mL to 614 AU/mL, and subculture test indicted that the hereditary character of high productivity of W-6 was stable.Then the fermentation medium of the mutant strain W-6 was optimized after the single factor experiments based on MRS fermentation medium. In order to screen an optimum medium which was fit for the fermentation of high-yield strain W-6, the best concentration of inorganic chemicals, carbon resource and nitrogen resource was selected by the orthogonal design method. The results indicated that the optimal fermentation medium for bacteriocin production was as follows: glucose 1.5%,fructose1%,lactose1%,peptone2%,extractum carnis0.5%,yeast power0.1%,NaAc 0.025%,K₂HPO₄ 0.02%,MgSO₄·7H₂O 0.01%,MnSO₄·H₂O 0.0025%,Tween 80 1mL/L,the best temperature was 37℃,the optimum initial pH for producing bacteriocin was 6.0,the optimum inoculating amount and seed age was 4%. Under this fermentation medium condition, the bacteriocin activity of W-6 was increasing by 19%.