Damage Mechanism and Protective Measures of Lactate and Osmotic Stress on Lactobacillus casei Zhang
Objective:To investigate the inhibitory effects of lactate and osmotic stress on Lactobacillus casei Zhang and to find solutions.Methods:The organic salt stress and osmotic pressure stress were created by using sodium lactate,am-monium lactate and sodium chloride,respectively,to determine the concentration of complete inhibition and plot the os-motic resistance curve,and the physiological damage to LCZ and the protective effect of compatible solutes were ob-served by measuring the density of the bacteria,the number of viable bacteria and cell damage.The key factors of os-motic pressure elevation were explored by batch culture and constant pH batch culture,and the effect of osmotic pres-sure reduction was achieved by diluting the fermentation broth,and the changes of bacterial density,viable bacterial count and dry weight yield of the samples were measured after dilution.Results:L-proline has a significant protective effect on LCZ biomass accumulation and cell activity under hypertonic environment,and the optimal addition amount is 2 g/L.The diluted fermentation broth treatment has a significant effect on the density and viable count of bacteria in constant pH supplemented culture.The final fermentation broth OD600nmand viable bacteria count could reach 19.68±0.429 and(3.439±0.110)×1010 CFU/mL,which were 1.61 and 1.46 times of the undiluted treatment,respectively.Conclusion:L-proline can alleviate the activity damage of LCZ under hypertonicity to a certain extent,and reducing the osmotic pressure at the later stage of fermentation by diluting the fermentation broth treatment can greatly improve the fermenta-tion level and cell activity,which can provide reference for industrial production and application.
Lactobacillus casei Zhanglactate stressosmotic stresscompatible solutehigh density fermentation
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