Study On The Factors Affecting The Stress Reaction Of Lactic Acid Bacteria And Its Thermotolerance

As a kind of probiotics.Lactic acid bacteria(LAB)can improve and balance the intestinal micro-ecological environment,enhance host immunity and reduce inflammation.It is now widely used in food,medicine,and other industries.Due to the inability of drying and storage,the production cost of lactic acid bacteria is high,the preservation period is short,and the application effect and application surface are limited.In this paper,a strain of Lactobacillus casei with good probiotic effects was selected for acid stress,heat stress and salt stress,the influencing factors of stress response were studied.It was found that after combined stress,it could be significantly improved heat resistance.The main results were as follows:1)Acid stress,salt stress and heat stress can improve the heat resistance of Lactobacillus casei.After 30 min of stress treatment in the pH4 environment,the heat resistance increased by 3.46 times.After 4%NaCl stress treatment for 30 min,the heat resistance increased by 4.15 times.After heat treatment at 50?for 3 h,the heat resistance increased by 2.01 times.After treatment with 4%NaCl stress for 30 min,and then treated with water ebath at 50?for 3 h,the heat resistance was increased by21 times.2)The Lactobacillus casei cultured to the end of the logarithmic phase was subjected to stress treatment at a concentration of 2×10~100 CFU/mL,and the heat resistance was improved by nearly 7 times,compared with 10~9 CFU/mL.3)The chemical composition and content of the bacterial suspension can affect the heat resistance.When composed with following substances in the bacterial suspension:glucose 20 g/L;peptone 10 g/L,beef powder 8 g/L;Tween-80 1.0 g/L;magnesium sulfate heptahydrate 0.2 g/L;ammonium citrate 2.0 g/L,and adjust pH to7.0,compared with the physiological saline suspension,the heat resistance increased by 126 times.4)Adding certain kinds of amino acids during the cultivation process can increase the heat resistance of the lactic acid bacteria.When 50 mM aspartic acid,tryptophan,glutamic acid,cysteine and histidine were added to the MRS liquid medium respectively,the heat resistance was increased by 27 times,26 times,27times,20 times,and 13 times.5)Continuous moderate heat stress can improve its heat resistance significantly.The activated bacterial solution was inoculated into a fresh MRS medium with 2%(vol/vol),and cultured in a constant temperature incubator at 43?until the end of the logarithm,and inoculated again to a fresh MRS culture with 2%.In the base,the operation was repeated,the operation was repeated 60 days,and the heat resistance was improved by 94 times compared with the original strain.Select the lactic acid bacteria in the late phase of the logarithm and treated with a combination stressful environment.Resuspend the cells with chemical substance described above,added drying protectant,and adjust the bacterial concentration to 2×10~100 CFU/mL.After blast drying,the survival rate was 42%,and the survival rate was maintained at about 75%after storage for 60 days at 4?.The survival rate of the lactic acid bacteria powder without any treatment and without the drying protection agent was only 7%,and the survival rate after 60 days storage at 4?was 40%.there is almost 10 times between two kinds of drying methods.