Abstract: This study examined the effect of probiotics on flavor formation in cheese. Lactobacillus plantarum 1-2, isolated from Tibetan kefir, was added at a level of 8.0 (lg(CFU/mL)) or 9.0 (lg(CFU/mL)) to pasteurized milk and added at 8.0 (lg(CFU/g)) to milk curds after whey draining, separately, which were then processed into Cheddar cheese. The aim was to determine the effect of inoculation methods, inoculum size and ripening time on the volatile flavor composition of cheese. By using solid phase microextraction coupled to gas chromatography-mass spectrometry (SPME-GC-MS), a total of 26 and 30 flavor compounds were detected in the control and probiotic cheeses, respectively. Addition of the probiotic L. plantarum 1-2 resulted in the formation of four unique volatile flavors, namely ethylbenzene, dodecane, hexanol and acetone. Ripening time had the greatest effect on cheese flavor. Benzene content in the probiotic cheese group was increased significantly with ripening time, but in the control group, benzene was not detected until after 12 weeks of ripening. The viable count of L. plantarum 1-2 also had a significant impact on cheese volatile flavor. Different addition methods and quantities of the probiotic strain had similar effects on the volatile flavor compounds in cheese, with the largest effect being observed on butyric acid. In the probiotic cheese group, butyric acid content reached the maximum after 12 weeks of maturation, showing a 3.96-fold increase compared with the control group. Cheeses made from pasteurized milk with different quantities of L. plantarum 1-2 added had different compositions of volatile compounds. However, addition of the probiotic strain at 9.0 (lg(CFU/mL)) to pasteurized milk and at 8.0 (lg(CFU/g)) to milk curds after whey draining had a similar effect on the composition of volatile compounds (P < 0.05). These results can provide an experimental basis for improving the processing and flavor quality of probiotic cheese.

Key words: probiotics, Lactobacillus plantarum, Cheddar cheese, flavor