Abstract: In order to improve the freeze-drying survival rate and the acid resistance of lyophilized powder of Lactobacillus casei CCFM711, cells were lyophilized with different acid-resistant materials, and with sugars and proteins as protectants for freeze-drying. The lyophilized cell powder was then tested and compared with the sodium alginate microcapsules prepared by the optimized emulsification method. Finally, the vacuum freeze-drying process was optimized. The results showed that stachyose combined with sodium alginate and sodium caseinate, respectively, could simultaneously improve the survival rate in freeze-drying and the acid resistance. Using stachyose as protectant for freeze-drying in preparation of sodium alginate wet microcapsules, the survival rate of bacteria in acidic environment could be significantly improved, but the acid resistance was significantly reduced, which was only (0.37±0.28) %, much less than un-coated lyophilized powder (19.56±1.83) %. Stachyose (100g/L) was used as the protectant for freeze-drying, and sodium caseinate (10 g/L) as the optimal wall material. Mixing the bacterial suspension and the protectants at the ratio of 2∶5, a freeze-drying survival rate of (59.43±6.28) % was obtained, while the highest survival rate was (34.16±7.18) % after 2 hours' treatment at pH 2.5, about 8 times of the control. This study provides guidance for the preparation of lyophilized powder of L. casei.
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