Abstract: In order to analyze the role of Lactobacillus casei cell surface substances during the freeze-drying process, the surface substances stripped conditions were optimized. The freeze-drying survival rate of the strains with different protective agents, and the total amount and composition of the surface substances were then determined after the surface substances were stripped off. The surface substances content of L.casei cultured in medium with different carbon-nitrogen ratios and different carbon sources were determined, and the relationship between the amount of surface substances and the freeze-drying survival rate was investigated. The results showed that the surface substances of L.casei 17005, 173011CQQJ3 and PS5-4 were effectively stripped off in the conditions of 90 W/6 min, 90 W/12 min and 90 W/12 min, respectively. The protein content in the surface substances was about 3 times as much as polysaccharides. With trehalose or stachyose as cryoprotective agents, the lyophilization survival rate of cells without surface substance was improved, and inulin was on the contrary. With arabinose as carbon source, L.casei produced fewer surface substances than glucose. Under the condition of low carbon-nitrogen ratio, the amount of surface substances was also effectively reduced. The smaller amount of surface substance was beneficial to improve the lyophilized survival rate of bacterial cells collected during the phase time when using trehalose or stachyose as cryoprotectants. The conclusions provided guidance for the improvement of the survival rate of lyophilized L.casei and the number of viable cells per unit mass of lyophilized bacterial powder.
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