Supplement C18:1 in Culture Medium to Improve Survival Rate and Fermentation Activity of Lyophilization of Lacticaseibacillus paracasei L9.

This study explored the impact of C18:1 fatty acid supplementation in culture medium on the survival rate, fermentation activity, and membrane stability of Lacticaseibacillus paracasei L9 during freeze-drying. Cells cultured in medium supplemented with C18:1 (0.2 mg/ml) exhibited a higher survival rate (95.38%) after freeze-drying compared to the control (83.56%). The fermentation activity of the freeze-dried powder was significantly enhanced, with improvements in viable count (Δ viable counts: 1.79 Log CFU/ml), pH reduction (Δ pH: 2.03), and titratable acidity (Δ titratable acidity: 99.4 °T) in skim milk. Supplementation with C18:1 increased the activity of key enzymes, such as β-galactosidase (13.25 U/ml) and lactate dehydrogenase (2.16 U), while reducing cell membrane permeability. The addition of C18:1 also modulated the expression of membrane synthesis-related genes, including plsX and YfhO, and altered the membrane fatty acid composition by increasing the proportion of unsaturated fatty acids (UFA). Specifically, the proportion of UFA in the membrane increased from 53.36% in the freeze-dried control to 63.28% in the C18:1-supplemented group. These results indicate that C18:1 supplementation improves cell membrane stability and fermentation activity by modulating gene expression and membrane fatty acid composition, thereby enhancing the freeze-drying tolerance of L. paracasei L9.