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The aim of this study was to examine the fermentation characteristics of a novel Leuconostoc mesenteroides strain (XR1) and to investigate the effect of XR1 exopolysaccharides (EPS) on the microstructure, texture and rheological properties of yoghurt. The novel Leuconostoc mesenteroides strain (XR1) was isolated from wild kefir grains obtained from Xinjiang Province. The results showed that XR1 had good EPS production capacity and favourable fermentation performance. The addition of XR1 EPS to fermented milk effectively improved the water-holding capacity (WHC) of the fermented milk and changed its microstructure. In subsequent fermentation studies, the XR1 strain was found to be a compatible strain, and the steric barrier formed between XR1 EPS and the fermented milk proteins enhanced its viscoelastic properties. Rheology studies indicated that fermented milk supplemented with EPS possessed a higher modulus (G', G'' ) and complex viscosity. Thus, these results indicate that XR1 EPS are useful as a natural organic additive that can replace chemical additives in dairy products.

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.