Sodium l-glutamate improves the lyophilization survival rate of Lactiplantibacillus plantarum L5 by regulating cellular pyruvate

Lyophilization is a crucial procedure for maintaining probiotic viability. This study aimed to screen the optimal protective agent for lyophilization and explore its potential protective mechanism on Lactiplantibacillus plantarum L5, which has a sleep-promoting function. The results showed that sodium L-glutamate is the optimal protective agent, with a survival rate of over 90%. After storage at 4°C for 6 months, the viable bacteria count remained stable at 4.80×1011 CFU/g. Under the protection of sodium L-glutamate, the lyophilized powder maintained a gastric juice tolerance rate of over 90%, and the auto-agglutination rate and acid-producing activity were similar to those before lyophilization. Scanning electron microscope and fourier infrared spectroscopy observations showed that the cellular structure of the lyophilized powder remained relatively stable. Finally, we found that the pyruvate content eventually accumulated through transcriptomic analysis, which may account for the high survival rate of L. plantarum L5 during the lyophilization process.