This experiment studied the changes of pH, acidity, microbial counts and utilization of lactose during kefir fermentation. The results showed that pH of kefir was decreased sharply, and its value dropped to 4. 102 from 6. 798 and the acidity rose to 96.9°T from 16. 1°T after fermentation of 24 h. In addition, microbial counts were evaluated. The colony counts of lactococcus were higher than lactobacillus in the initial fermentation stage. At the end of fermentation, the colony counts of lactococcus, lactobacillus and yeast reached 1.6 × 10~7 CFU/mL, 7.7 × 10~7 CFU/mL, 1.1 × 10~5 CFU/mL respectively. The fermentation of kefir resulted that the content of lactose was decreased significantly, and its value declined to 1.90 mg/mL from 4.05 mg/mL in the fermentative period.%以开菲尔粒为发酵剂发酵牛乳,跟踪发酵过程中pH、酸度、微生物数的变化及乳糖利用情况.结果表明,经开菲尔粒发酵后牛乳的pH值降幅很大,发酵24 h后pH值从6.798降到4.102,酸度则从16.1°T上升到96.9°T.在发酵初始阶段,开菲尔乳中乳球菌为优势菌,乳杆菌次之;到发酵结束时,乳杆菌为优势菌,乳球菌次之,乳球菌、乳杆菌和酵母菌分别达到1.6×10~7 CFU/mL.7.7×10~7 CFU/mL和1.1×10~5 CFU/mL.开菲尔发酵也导致了发酵乳中乳糖含量的显著降低,发酵终点时开菲尔乳中乳糖含量从4.05 mg/mL降为1.90 mg/mL.
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