自然发酵牛乳中乳酸菌和酵母菌的活菌动态变化

构建三批次各100 kg牛乳自然发酵体系，通过分析乳酸菌和酵母菌的活菌动态变化，对两者间的相互作用进行研究。结果表明，在（20±1）℃的自然发酵温度下，持续发酵56 h，pH值下降至4.6～5.0，发酵牛乳逐渐分层并形成上层奶嚼口和下层凝乳。连续三个批次发酵牛乳中奶嚼口和凝乳的乳酸菌平均活菌数分别为（12.02±1.21）lg（CFU/mL）和（11.54±1.30）lg（CFU/mL），差异不显著（P＞0.05）；而凝乳中酵母菌平均活菌数[（6.39±0.60）lg（CFU/mL）]显著低于奶嚼口[（4.56±0.30）lg（CFU/mL）]（P＜0.05）。活菌动态变化表明，在牛乳自然发酵过程中，乳酸菌的生长具有延迟期、对数期、稳定期三个典型阶段，而酵母菌没有明显的对数期，随着乳酸菌的生长反而抑制酵母菌的生长。

Dynamic changes of viable numbers of lactic acid bacteria and yeasts in naturally fermented milk

A system of three batches of 100 kg milk with natural fermentation was constructed, and the interaction between lactic acid bacteria and yeasts was studied by analyzing the dynamic changes of viable numbers. The results showed that the fermented milk gradually layered and formed the upper milk chew and lower curd under the natural fermentation temperature of (20±1) ℃ with continuous fermentation for 56 h and the decreased pH value 4.6-5.0. The average viable numbers of lactic acid bacteria in the milk chew and lower curd of three successive batches were (12.02±1.21)lg(CFU/ml) and (11.54±1.30)lg(CFU/ml), respectively, with no significant difference (P＞0.05). However, the viable count of yeasts in the curd (6.39±0.60) lg(CFU/ml)was significantly lower than that in the milk chew (4.56±0.30) lg(CFU/ml) (P＜0.05). The dynamic changes of viable bacteria indicated that the growth of lactic acid bacteria had three typical stages: lag phase, logarithmic phase and stationary phase, while yeasts had no logarithmic phase during the natural fermentation process of milk. With the growth of lactic acid bacteria, the growth of yeast was inhibited.