Abstract: The effect of protease and lipase added individually and in combination on fermentation characteristics and flavor of cream and whey mixture was investigated by determining the changes in viable cell number of lactic acid bacteria, titratable acidity, pH value and volatile flavor components. After 60 h fermentation, the volatile flavor components were extracted by using headspace solid-phase microextraction (HS-SPME) and analyzed by gas chromatography-mass spectrometry (GC-MS) combined with principal component analysis and sensory evaluation was also performed. The results showed that carboxylic acids, ketones and esters were the main volatile flavor components isolated by GC-MS. Protease promoted the growth of lactic acid bacteria, acid production and the formation of ketones and improved the flavor quality. Lipase significantly increased titratable acidity, suppressed the growth of lactic acid bacteria acid production, pronouncedly promoted the generation of carboxylic acids, resulted in the formation of esters, evidently improved and enriched the flavor of the fermented system. Protease and lipase added in combination increased the production of esters, significantly enhanced the aroma, remarkably improved the flavor and attenuated the sour taste of carboxylic acids, had the biggest influence as revealed through principal component analysis. Protease and lipase could improve the quality of flavor, and their combination mitigated sour taste by the sensory evaluation.

Key words: cream, whey, protease, lipase, fermented characteristics, flavor