Saccharomyces boulardii (S. boulardii) is widely adopted in the diarrhea treatment for humans or livestock, so guaranteeing the survival rate of S. boulardii is the critical issue during freeze-drying process. In this study, the survival rate of S. boulardii with composite cryoprotectants during freeze-drying procedure and the subsequent storage were investigated. With the aid of response surface method, the composite cryoprotectants were comprehensively optimized to be lactose of 21.24%, trehalose of 22.00%, and sodium glutamate of 4.00%, contributing to the supreme survival rate of S. boulardii of 64.22 ± 1.35% with the viable cell number of 9.5 ± 0.07 × 109 CFU/g, which was very close to the expected rate of 65.55% with a number of 9.6 × 109 CFU/g. The accelerated storage test demonstrated that the inactivation rate constant of the freeze-dried S. boulardii powder was k-18 = 8.04 × 10-6. In addition, the freeze-dried goat milk powder results exhibited that the inactivation rate constants were k4 = 4.48 × 10-4 and k25 = 9.72 × 10-3 under 4 and 25 °C, respectively. This work provides a composite cryoprotectant formulation that has a good protective effect for the probiotic S. boulardii during freeze-drying process, possessing the potential application prospect in food, medicine, and even feed industry.
Keywords: Cryoprotectant; response surface method; storage stability.