Abstract: Objective:The formulation of protective agent added in vacuum freeze-drying process was optimized to obtain bread yeast 3G-28 freeze-drying powder with good fermentation performance.Methods:On the basis of single factor experiments of skim milk powder, sucrose, Tween-80, Arabic gum, cyclodextrin and glycerin, the formula of compound freeze-drying protectant was optimized by response surface experiment, and the ferment power, trehalose content, sucrase activity and flavor in fermentation liquid of yeast freeze-drying powder were studied.Results:The order of influence of each factor on the number of viable bacteria in bread yeast freeze-dried powder was as follows: The concentration of glycerol > the concentration of sucrose > the concentration of skim milk powder > the concentration of β-cyclodextrin. The formula of the best compound freeze-drying protective agent was as follows: Glycerin 4.7%, skimmed milk powder 20%, β-cyclodextrin 15%, sucrose 5%. The viable quantity of bread yeast freeze-dried powder was 36.89×10⁹ PCS / mL. The fermentation capacity of baker's yeast 3G-28 freeze-dried powder was 214 mg/h/g, the content of trehalose was 44.22 mg/g, and the activity of sucrase was 20.27 U/g. Compared with the freeze-dried powder of commercially available yeast and the freeze-dried powder of the initial strain of yeast, the yeast showed higher biological activity. In terms of flavor, the content of alcohol in bread yeast 3G-28 freeze-dried powder was the highest compared with the other two, showing good practicability.ConclusionThe optimum formulation of the baker's yeast 3G-28 freeze-drying powder was studied, and the baker's yeast freeze-drying powder with better biological activity was obtained, which had a good prospect in improving the quality of bread products and in the application of microbial industrialization.