Research On Heat Stress Response Of Lactobacillus Plantarum

Poor stability of probiotic products during food processing and storage has become a technological bottleneck in the probiotic industry, and to enrich the stability of probiotic products by heat, acid and salt adaptation has been widely studied. In this study we investigated the heat stress response of Lactobacillus plantarum in different strains, growth phases and culture conditions, in order to reveal the factors influencing heat stress response and their regulation mechanisms. First 45℃for 30 min was selected for the heat adaptation and 55℃for 15 min was selected for the lethal evaluation. Heat resistance and heat stress response of two Lactobacillus plantarum strains Lp529 and LP-Onlly were evaluated. L. plantarum Lp529 was more thermotolerant than LP-Onlly, but LP-Onlly was more inducible by heat adaptation. Then effect of growth phases and culture conditions on heat stress response of L. plantarum LP-Onlly was examined. The mid-log-phase culture of L. plantarum LP-Onlly was more inducible by heat adaptation than stationary-phase one. It revealed that heat stress response in stationary-phase cells of L. plantarum LP-Onlly was affected by cells density and pH. By adjusting pH from 4.3 to 7.0 before heat adaptation, the thermotolerance factor was significantly improved, and pH 6.5 was determined as the optimal pH for heat adaptation. After heat-adapted at pH 6.5, the thermotolerance and long-storage stability of stationary-phase cells were 2700-fold and 6-fold greater than control, respectively. Besides, thermotolerance of stationary phase cells by the end of the fermentation increased 11-, 38-, 11-fold after prior heat-adapted at seed, mid-log phase and stationary phase. It indicated that benefits of heat adaptation can pass through generations. Five major heat shock protein genes, dnaK, dnaJ, grpE, groES, groEL were determined in L. plantarum 529 and LP-Onlly, and characterized as highly conservative. Real-time reverse transcription PCR analysis of these five heat shock protein genes in heat stress response revealed that mRNA levels were induced by heat adaptation and presented tightly related to heat resistance and heat stress response of plantarum LP-Onlly. After adjusting pH for heat adaptation form 4.3 to 6.5 in stationary-phase culture, the heat-inductive expression of five genes was up-regulated.