| The probiotics prepared by vacuum freeze-drying have the advantages of convenient transportation and storage.The probiotics prepared by drying under room temperature do not need cold chain,which can greatly reduce the cost of transportation and storage.However,there are problems of rapid decline of bacterial activity and low survival rate.Therefore,it is of great significance to improve the stability of probiotics at room temperature.In this paper,5 Lactobacillus plants with prebiotic characteristics were used as the research object to study the effect of GSH on the freeze-drying survival rate and storage stability of the strains by adding glutathione(GSH)to their growth medium and protective agent respectively.Taking Lactobacillus LIP-1(P1)as an example,the mechanism of GSH improving the stability of room temperature storage was studied.The results showed that the freeze-drying survival rate of Lactobacillus P1 and Lactobacillus pc26153(P3)increased by 5.4% and 8.2% respectively compared with the control group without GSH.After 8 weeks of room temperature storage,the survival rate increased by 37.9% and 21.7% respectively.But there was no significant effect on Lactobacillus pc22301(P2),Lactobacillus plantarum IMAU70010(P4)and Lactobacillus IMAU 10120(P5).The results showed that the concentrations of GSH in plantarum P1 and P3 were 134.0 ng/mg protein and 42.7 ng/mg protein respectively,but GSH was not detected in the other three strains.GSH added to the protective agent had no effect on the freezedrying survival rate of 5 Lactobacillus plants,but compared with the control group without GSH,the survival rate after 8 weeks storage at room temperature increased by 10% to 16%.The mechanism of GSH improving the stability of Lactobacillus P1 at room temperature was studied.It was found that GSH increased the antioxidant capacity of the strain.The scavenging rate of DPPH and hydroxy radicals was increased by 2.2 times and4.0 times respectively,and the reduction activity was increased by 2.6 times.GSH had no effect on SOD activity in culture(p < 0.05),but the enzyme activity in medium group was significantly higher than that of control group(p < 0.05).The results showed that the ROS level in the cells was significantly lower than that of the control group(p < 0.05).The results showed that the percentage of cell membrane damage in control group was much higher than that in experimental group after 8 weeks storage.This indicated that GSH maintained the integrity of cell membrane during storage;The results showed that the conductivity of medium group was lower than that of control group,which indicated that the electrolyte leakage in the medium group was less during storage period,which further indicated that GSH maintained the integrity of cell membrane better.The results showed that the ratio of unsaturated fatty acids to saturated fatty acids(U / S)decreased from 0.94 to 0.49 in the control group after 8 weeks storage,and the U / S of medium group was 0.74,which indicated that GSH significantly reduced the oxidation rate and degree of unsaturated fatty acids.The results showed that for 5 Lactobacillus plants,the effect of GSH on freeze-drying survival and room temperature storage was better than that of the protective agent.The reason may be that the strain could transfer GSH to the cell during the growth period and inhibit the formation of intracellular free radicals,GSH in the protective agent could not enter the cell during storage.For Lactobacillus P1,GSH can reduce the ROS level in the initial stage of storage by improving the antioxidant capacity of the strain;The activity of SOD in the long-term storage process was maintained,the ROS production was inhibited during storage period,the oxidation degree of fatty acids was reduced,the structure and function of cell membrane were protected,and the stability of strain storage was improved.GSH can improve the storage stability of the strain,provided that the strain has the ability to obtain GSH from the medium. |
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