Abstract: [Objective] To study and compare the quality changes of homemade yogurt and commercial yogurt during storage. [Method] The quality changes of homemade yoghurt during fermentation were studied by means of lactic acid bacteria count,acidity and pH,and then compared with commercial yoghurt. [Result] In the process of homemade yogurt,3 h after fermentation,with the accumulation of lactic acid, the acidity increased,the pH value decreased,and the viable number of lactic acid bacteria increased significantly. After 7 h fermentation,the total number of lactic acid bacteria began to decrease,and the increasing trend of acidity and the decreasing trend of pH slowed down. In the storage stage,with the increase of storage time,the quality changes of all kinds of yogurt are basically the same,the content of lactic acid bacteria first increases and then decreases,the pH value decreases,and the acidity increases. Under the condition of 4℃ storage,the quality change is less than 25℃. [Conclusion]The quality of yoghurt decreases more slowly under refrigerated treatment. When making or buying yoghurt,we should choose refrigerated treatment as much as possible and drink it as soon as possible after opening the cover. The two kinds of yogurt have different characteristics,and consumers can choose according to their needs. In conclusion,this study provided a reference for the safe storage of yogurt.

Key words: homemade yogurt, commercially available yogurt, fermentation, storage, quality change