| As a member of probiotics,lactic acid bacteria can not only promote the growth and development of animals,balance the intestinal microenvironment,but also enhance the immunity of animals and improve their resistance to disease.They are used in many fields such as food,medicine,agriculture,industry,and so on.There are many benefits to using probiotics and live bacteria,but the use of more live bacteria is not necessarily better.If large doses of live bacteria are used for a long time,it can cause safety issues such as bacterial infections,antibiotic resistance,and hypersensitivity reactions.Some studies have shown that the physiological functions of inactivated lactic acid bacteria are similar to those of live bacteria,and inactivated lactic acid bacteria have greater advantages over live lactic acid bacteria in terms of safety,stability,convenience,and synergy with antibiotics.In this study,Lactobacillus casei(ATCC393)was thermally inactivated.In order to explore the optimal thermal inactivation conditions,temperature(65℃,70℃,80℃)and time gradient(10min,20 min,30 min)were set respectively.Finally,the optimal thermal inactivation conditions were determined to be 80℃water bath heating for 10 min.Simultaneously align the height(1×10~8 CFU/m L),medium(1×10~7CFU/m L),Low(1×10~6 CFU/m L)adhesion ability of heat inactivated L.casei to intestinal epithelial cells(Caco-2)was evaluated at a concentration of 10~6 CFU/m L,and the results showed that the heat inactivated L.casei at various concentrations still had the ability to adhere to cells,and the medium concentration(1×10~7CFU/m L)has the best effect.To evaluate the immune effect of heat inactivated L.casei,C57BL/6J mice were used as experimental animals,and a high(1×10~8 CFU/m L),medium(1×10~7CFU/m L),Low(1×10~6CFU/m L)concentration heat inactivated Lactobacillus casei group and medium concentration(1×10~7CFU/m L)L.casei live bacteria control group(VC)and blank control group(PBS)were continuously administered for 14 days,0.3 m L/mouse/day,respectively.On the 7th and 14th days of administration,serum and spleen tissues were taken to detect growth and immune indicators,and on the 14th day of administration,a challenge test was conducted to evaluate the immune effect.The results of spleen index measurement showed that heat-inactivated Lactobacillus casei could promote the growth of mouse spleen,and the effect was most significant when using medium concentration.At the same time,the medium concentration of Lactobacillus casei also had a certain effect on promoting the growth of spleen.Calculate mouse spleen index by weighing mouse body weight and spleen weight,and detect mouse serum cytokines(IL-2,IL-6,IL-10,TFN-α、IFN-γ、SIg A)by ELISA method content,the expression of IL-2 in mouse spleen tissue was detected by q RT-PCR,and the immune protection of mice was tested by challenge test.The results showed that heat inactivated L.casei could promote the growth of mouse spleen,increase the content of related cytokines in serum,and upregulate the expression of IL-2 m RNA pairs.At the same time,the challenge test results showed that the medium concentration(1×10~7CFU/m L)of heat inactivated L.casei had the best immune protection effect,reaching 37.5%.This study provides a theoretical basis for the further development and application of heat inactivated lactic acid bacteria. |
