Screening of the freeze‐drying protective agent for high‐quality milk beer yeast ( Kluyveromyces marxianus ) and optimization of freeze‐drying process conditions

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Milk beer is a new type of milk beverage produced by two-step fermentation of lactic acid bacteria and yeast and created first in China. Yeast is the key strain of milk beer fermentation, which determines the flavor and quality of milk beer. In this study, the preparation process of high-quality yeast strain MJ1 active freeze-dried powder suitable for milk beer fermentation was optimized. Results showed that the optimal freeze-dried protective agent was used: sucrose 11.27%, mannitol 4.88%, maltodextrin 15.43%, skimmed milk powder 7.82%, and applying the optimal freeze-drying conditions: rotation speed 6,000 rpm, centrifugation time 15 min, the mixing ratio of centrifugal bacterial sludge and the protective agent is 1:1.5, the mixing equilibrium time is 30 min, the cell survival rate of strain MJ1 can reach 90.21% ± 1.04%. It laid the foundation for the preparation of active freeze-dried yeast powder and the industrial production of milk beer. Novelty impact statement (1) The formulation and conditions of the freeze-dried protectant of Kluyveromyces marxianus yeast strain MJ1 were optimized to improve the cell survival rate of the freeze-dried yeast powder, (2) the optimal storage conditions of the freeze-dried yeast powder of strain MJ1 were screened to provide theoretical reference for the long-term storage of freeze-dried yeast powder, and (3) the fermentation performance of the freeze-dried yeast powder of strain MJ1 was verified, which provided a reliable basis for the industrial production of milk beer.