Harnessing L-Cysteine to enhance lyophilization tolerance in Lactiplantibacillus plantarum: Insights into cellular protection mechanisms

Enhancing the viability of lyophilized microbial strains by modulating their physiological metabolism is an important focus of microbiological research. Certain amino acids have been shown to influence the physiology of microbial strains; however, their effect on strain survival during lyophilization remains largely unexplored. In this study, we employed five different amino acids to investigate the potential correlation between amino acid supplementation and the viability of Lactiplantibacillus plantarum during lyophilization. We discovered that the addition of 0.05 g/L L-cysteine could significantly improve the post-lyophilization viability of all four L. plantarum strains after culture. Subsequently, the mechanisms underlying this enhancement were elucidated using L. plantarum LIP-1 as a type strain. The results showed that L. plantarum metabolised L-cysteine to produce glutathione, which in turn decreased the levels of reactive oxygen species, enhanced hydroxyl radical scavenging, inhibited the oxidation of unsaturated fatty acids, and maintained cell membrane fluidity. As a result, cell membrane damage was attenuated, ultimately improving the lyophilization resistance of L. plantarum . • There are few reports on the effect of amino acids on freeze-drying resistance. • L-cysteine in the medium improved the freeze-drying survival rate of the strain. • The mechanism was the protection of cysteine on the cell membrane of the strain. • L-cysteine reduced cell membrane unsaturated fatty-acid oxidation.