Abstract: The effects of different concentrations of oleic acid on the growth and freeze-drying survival of Lactobacillus plantarum LIP-1 were studied. The results showed that low concentration of oleic acid (≤ 0.2 g/L) could increase the viable count and freeze-drying survival rate in MRS medium. The optimum concentration of oleic acid was 0.1 g/L, increasing the viable bacteria count and the freeze-drying survival rate by 9 × 108 CFU/mL and 8.38% as compared with the blank control group without oleic acid, respectively. When the concentration of oleic acid was higher than 0.3 g/L, the growth of the strain was inhibited. The fatty acid composition of the cell membrane was analyzed by gas chromatography (GC). The results showed that the ratio of unsaturated fatty acids to saturated fatty acids (UFA/SFA) was increased by 0.45% and the proportion of cyclopropane fatty acids by 8.35% in the 0.1 g/L oleic acid group as compared with the blank control group. There was a significantly negative correlation between stearic acid and oleic acid as well as between palmitic acid and cyclopropane fatty acids. The number of cells exhibiting green fluorescence in the experimental group was significantly higher than that in the control group, which indicated that the integrity of the cell membrane was maintained well in the experimental group during freeze-drying. The activity of β-galactosidase in the supernatant of freeze-dried L. plantarum LIP-1 in the experimental group was lower than that in the MRS group, indicating that low concentration of oleic acid (≤ 0.2 g/L) could maintain the integrity of the cell membrane and reduce the leakage of β-galactosidase. Conclusion: Adding low concentration oleic acid to the medium can promote the synthesis of cyclopropane fatty acids, induce the transformation of saturated fatty acids into unsaturated fatty acids, and improve the resistance of this strain to freeze-drying.

Key words: oleic acid, Lactobacillus plantarum LIP-1, freeze-drying, freeze-drying survival rate, cell membrane, unsaturated fatty acid, cyclopropane fatty acid