Abstract: Proteolysis is an important way of flavor generation during cheese ripening. Manual milking is always applied to free-range dairy cows and small-scale dairy farms, which now still accounts for a large proportion of the total in China, and it results in retention of somatic cells (SCs) in raw milk, affecting cheese ripening and flavor. However, the effect of somatic cells on volatile flavor compounds in cheese through proteolysis has not yet been elucidated clearly. In the present study, three skim milks containing different somatic cell counts were used for cheese manufacture after being analyzed for somatic cell composition, and the changes in protease activity and proteolysis level during 90 days of ripening, as well as the volatile flavor compounds and texture of the ripened cheeses were measured. It was shown that cheese with higher somatic cell count (SCC) had higher levels of both protease activity and proteolysis of αs2-casein and that the SCC in raw milk had different influences on the volatile flavor compounds and texture of cheese. Increasing SCC in an appropriate range (10 × 104 to 30 × 104 cells/mL) was favorable for the formation of cheese flavor. The amount of 3-hydroxy-2-butanone, responsible for the characteristic flavor of cheese, in the medium SCC group was the highest (34.57%), which was 1.2 and 1.6 times higher than that of the low (28.64%) and high (20.72%) SCC groups, respectively. Excessive somatic cells (more than 86 × 104 cells/mL) in raw milk caused excessive hydrolysis and off-flavor generation during cheese ripening. More octanal, furfural, octyl ketone, and hexanal as unfavorable cheese flavor were detected in the highest SCC group.

Key words: somatic cells, cheese, proteolysis, flavor