C18:1 Improves the Freeze-Drying Resistance of Lactobacillus plantarum by Maintaining the Cell Membrane

Increasing knowledge about lactic acid bacteria as fermentation starters and probiotics to improve health has led to a growing awareness of their application potential. Despite a long history of applying cryoprotectants, the maintenance of probiotic viability is still a major challenge. In this study, we implemented a strategy and explored its mechanisms in detail. We found that the survival rates after freeze-drying were positively correlated with the relative concentration of the octadecenoic acid (C18:1) and with the ratio of unsaturated to saturated FAs (U/S ratio). The addition of C18:1 significantly improved the survival of L. plantarum after freeze-drying. Contrary to the most commonly used cryoprotectants, the addition of C18:1 did not affect the glass transition temperature or collapse temperature. We predicted that the cell membrane characteristics would be significantly degraded during the drying stage, but C18:1 can effectively maintain the cell membrane integrity and fluidity. Our experiments confirmed those predictions, and simultaneously found that the enzyme activities of key enzymes of glucose metabolism were increased compared with the control group. These finding indicate that C18:1 might serve as a lyoprotectant to maintain the cell membrane integrity and fluidity, and thereby increasing the survival rate of L. plantarum after freeze-drying. This study constitutes a strategy to safeguard bacterial viability.