甘肃藏区自然发酵牦牛乳中优良乳酸菌的筛选及鉴定

Isolation and Identification of Lactic Acid Bacteria with High Fermentation Performance from Naturally Fermented Yak Yogurt in Tibetan Pastoral Areas of Gansu

从甘肃藏区采集的23份自然发酵牦牛乳中分离出的195株乳酸菌，经遗传稳定性、凝乳时间、滴定酸度、保水率及感官评价初筛得到12株发酵性能较好的菌株。再通过酸化能力、后酸化能力、冷藏期间活菌数和黏度的变化及产香能力的测定，最终筛选出5株性能优良的乳酸菌。这5株菌凝乳时间在4～6h之间，凝乳时的滴定酸度在75.90～83.87°T之间；冷藏期间滴定酸度增加了13.72～21.16°T、活菌数含量为107～1011CFU/mL、黏度为3.01～8.21Pa·s；产生的乙醛和双乙酰含量分别为11.00～42.68μg/mL和2.91～13.18μg/mL。通过16S rDNA分子鉴定，菌株Q3为乳酸乳球菌乳酸亚种（Lactococcus lactis subsp. lactis），Q4为嗜热链球菌（Streptococcus thermophilus），G3、G4、G5为德氏乳杆菌保加利亚亚种 （Lactobacillus delbrueckii subsp. bulgaricus）。这5株乳酸菌可以应用到发酵乳制品的工业化生产中。

A total of 195 strains of lactic acid bacteria （LAB） were isolated from 23 naturally fermented yak yogurt samples collected from different Tibetan pastoral areas of Gansu province. Totally 12 LAB strains showing better fermentation performance were obtained through preliminary selection based on genetic stability, coagulation time, titratable acidity, water retention and sensory evaluation. Finally, 5 strains of LAB with excellent fermentation performance were selected by assessing acidification ability, post-acidification capacity, viability and viscosity during cold storage, and aroma-producing capacity. The coagulation time and titratable acidity of the 5 strains were 4 to 6 h and 75.90 to 83.87 °T, respectively. During cold storage, the value of titratable acidity increased by 13.72 to 21.16 °T. The viable bacteria counts were 107 to 1011 CFU/mL and the viscosity values were 3.01 to 8.21 Pa？s. The contents of acetaldehyde and diacetyl were 11.00 to 42.68 μg/mL and 2.91 to 13.18 μg/mL, respectively. The results of 16S rDNA molecular identification showed that Q3 and Q4 were classified as Lactococcus lactis subsp. lactis and Streptococcus thermophilus, respectively while G3, G4 and G5 belonged to Lactobacillus delbrueckii subsp. bulgaricus. These 5 trains LAB is useful for industrial production of fermented dairy products.