Abstract: [Objective] To explore the correlation between various physicochemical and microbiological indicators in raw milk and the activity of protease.[Method] Taking raw milk from different regions as samples,the protease activity was determined using the Folin phenol method,and the effects of season and the composition raw milk（fat,protein,lactose,total solids,total bacterial count,somatic cell count） on the protease activity was analyzed accordingly.[Result] The effects of seasonal factors on protease activity：The enzyme activity was generally higher in winter than in summer,and a certain pastures in Ningxia showed a more obvious seasonal variation trend. The effect of raw milk components on protease activity：Among the physicochemical indicators,protein and fat content were significantly correlated with protease activity,while the changes in lactose content has no significant effect on enzyme activity;in terms of microbial indicators,the number of psychrophilic bacteria had a stronger explanatory power for the change in protease activity. In high-quality raw milk,the correlation between the somatic cell count and total bacterial count and protease activity was relatively weak.[Conclusion] The protease activity in raw milk is significantly affected by factors such as seasonal temperature changes,changes in protein content,and the composition of the dominant enzyme producing bacterial population. In-depth study of these factors is of great significance for the assessment of raw milk quality and the improvement of product quality.

Key words: raw material, protease, protein, physicochemical indicator, microbial indicator