Abstract:The effects of different fat content (7%, 14%, and 21%) and protein content (2.3% and 4.6%) on cream-whey fermentation liquid and the relationship between the composition of new flavor fermentation systems and fermentation characteristics were studied. Changes in the number of viable bacterial cells, titratable acidity, and pH value during the fermentation process were measured. The volatile flavor components were extracted using headspace solid-phase microextraction (HS-SPME), analyzed by gas chromatography-mass spectrometry (GC-MS) after fermentation for 60 h, and evaluated by sensory tests. The results showed that the increase in fat content had no influence on the proliferation of lactic acid bacteria or on the pH value at low protein levels, but suppressed the proliferation of lactic acid bacteria and prevented the decline in pH at high protein levels. In addition, increased fat content promoted the production of flavor and volatile compounds and inhibited the production of acids by the bacteria. Increased protein content promoted the proliferation of lactic acid bacteria, significantly increased the content of volatile flavor components, and slowed the decline in pH values. Moreover, increased protein content promoted the production of acids at low fat levels, but inhibited the production of acids at high fat levels. After 60 h of fermentation, the main volatile compounds in the system were acetic acid, butyric acid, 2,3-butanedione, and 3-hydroxy-2-butanone. The sensory evaluation showed that the mixed fermentation liquid with 14.0 % fat and 4.6 % protein had the best structural state and the strongest yoghurt flavor.
