Chemical And Microbiological Compositions And Identification Of Lactic Acid Bacteria In Traditional Fermented Milk Of Tibet In China

The chemical and microbiological compositions of forty-four traditional fermented milk samples were analyzed in this study. These samples were collected from different individual households in different region of Tibet. One hundred and seventy-one strains of lactic acid bacteria (LAB) were isolated from these samples. Moreover, traditional physiological and biochemical characteristically methods and 16S rDNA analysis were used to identify the species of these bacteria. This research provided the basic data for systematically understanding of the characteristics of traditional fermented milk in Tibet. For further exploitation and utilization of lactic acid bacteria in industrial development, this study can also give much useful information.The average content values of various indexes tested in these fourty-four samples were described as follows. Fat, protein, lactose, ash, calcium and phosphorus were 4.14±1.02 g/100mL, 4.59±2.67g/100mL, 2.64±1.21 g/100mL, 0.75±0.11g/100mL, 102.83±17.88mg/100mL and 94.29±18.31mg/100mL, respectively. Vitamin B1, B2, B6, C and free amino nitrogen were 0.196±0.155μg/g,1.546±0.474μg/g, 0.059±0.041μg/g, 1.504±0.924mg/100g and 4.413±1.984 mmol/L, respectively. The average pH values was 4.27±0.44, acidity aligned at 104.65±44.35°T, lactic acid leveled at 0.661±0.288 g/L, acetic acid content was 0.072±0.051g/L, citric acid content was 0.052±0.024g/L, succinic acid content as 0.014±0.007g/L and ethanol content was 3.68±0.75g/L. For most of the samples, the counts of lactic acid bacteria and yeasts were 7.08～9.71and 5.01~6.98log cfu/g, respectively. Generally, in these samples, the counts of the lactic acid bacteria were higher than those of the yeasts by one or two logarithm.Among the one hundred and seventy-one strains, rod bacteria ratio71.3% was higher than that of cocci 28.7%. Thus, rod bacteria were considered as a major population in these samples. In this study, Lactobacillus fermentum 29.9% and Lactobacillus casei 26.9% were the most predominant species among all the isolates. Moreover, the left isolates were identified as Lactobacillus plantarum, Lactobacillus helveticus, Lactobacillus curvatus, Lactococccus lactis subsp lactis, Lactococccus lactis subsp cremoris, Enterococcus duarus, Enterococcus faecium, Leuconostoc mesenteroicles subsp mesenteroides and Leuconostoc pseudomesenteroides.