Traditional Fermented Yak Milk Research Articles

Exploring the link between microbial community structure and flavour compounds of traditional fermented yak milk in Gannan region

Traditional fermented yak milk has immense cultural and nutritional significance for Tibetan herders. In this study, we investigated the microbial community structure and flavour compounds in traditional fermented yak milk from three distinct regions of Gannan to explore the relationship between microbial composition and flavour compounds. The findings revealed significant variations in flavour compounds and the bacterial microbiota among the samples from the three regions. The dominant species identified in fermented yak milk were Streptococcus salivarius subsp. Thermophilus, Lactobacillus helveticus, and Kluyveromyces marxianus. Bidirectional orthogonal partial least-squares (O2PLS) analysis highlighted five bacterial genera and three fungal genera as contributors to the production of flavour-related compounds. Furthermore, regression analysis revealed that the Lactobacillus and Streptococcus genera were associated with the production of 2,3-pentanedione as well as eight predicted KEGG pathways. These findings provide valuable insights into the intricate relationship between flavour compounds and microbiota in traditional fermented yak milk.

Research on bacterial community characteristics of traditional fermented yak milk in the Tibetan Plateau based on high-throughput sequencing.

The Tibetan Plateau has an abundance of yak milk resources. The complex microbiota found in traditional fermented yak milk produced and sold by local Tibetans endows the yak milk with unique quality characteristics such as tissue morphology, flavor, and function. However, the diversity of bacterial flora in traditional fermented yak milk have not been elucidated. In this study, 15 samples of fermented yak milk were collected for 16S rRNA high-throughput sequencing to analyze the bacterial community composition and function. After filtering for quality, 792,642 high-quality sequences were obtained, and 13 kinds of different phyla and 82 kinds of different genera were identified, of which the phylum Firmicutes (98.94%) was the dominant phylum, Lactobacillus (64.73%) and Streptococcus (28.48%) were identified as the dominant genus, in addition, the bacterial community richness and diversity were higher in Manang Village, followed by Bola Village. Bacterial community richness and diversity in Huage Village were relatively low. Based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) functional classification, the microorganisms in traditional fermented yak milk have rich metabolic functions (77.60%). These findings suggest that a large number of bacteria in traditional fermented yak milk contain abundant metabolic genes and can carry out a variety of growth and metabolic activities. This study established a theoretical foundation for further exploring the microbial flora of traditional fermented yak milk in Gannan.

Antioxidant properties of lactic acid bacteria isolated from traditional fermented yak milk and their probiotic effects on the oxidative senescence of Caenorhabditis elegans.

The objectives of the current study were to screen antioxidant lactic acid bacteria (LAB) strains isolated from traditionally fermented Tibetan yak milk, and to evaluate their probiotic effects on the oxidative senescence of Caenorhabditis elegans (C. elegans). A total of 10 LAB isolates were assessed for their antioxidant activity by in vitro assays, and three strains with high activity were selected for an investigation of their probiotic functions in C. elegans. The results indicated that Lactobacillus plantarum As21 showed high anti-oxidant capacity and had a high survival rate (64%) in a simulated gastrointestinal tract. The lifespan of C. elegans treated with As21 was increased by 34.5% compared to the control group. Strain As21 also showed improved motility and enhanced resistance to heat stress and H2O2 stimulation in C. elegans. Moreover, treatment with As21 reduced the production of age-related reactive oxygen species (ROS) and malondialdehyde (MDA) damage and promoted the production of the antioxidants superoxide dismutase (SOD), catalase (CAT) and glutathione GSH. These results suggest that Lactobacillus plantarum strain As21 could be a potential probiotic strain for retarding ageing and could be used in functional foods.

Characterization of the microbial community compositions and diversities in the traditional fermented yak milk from different ecotopes on the Qinghai-Tibetan plateau

This study investigated the bacterial and fungal diversities and compositions in the traditional fermented yak milk from 5 major ecotopes of the Qinghai-Tibetan plateau. Totally 47 lactic acid bacteria species or subspecies were found in the traditional fermented yak milk, and the dominant bacterial species were Lactobacillus delbrueckii, Streptococcus salivarius, and S. thermophiles. Although differences in the relative abundances of bacteria were found among the samples from 5 ecotopes, there were no correlations between the dominant lactic acid bacteria species and the pH of traditional fermented yak milk or altitude, longitude, and latitude of sampling sites. There were 9 yeast species and Saccharomyces cerevisiae, Pichia kudriavzevii and Debaryomyces hansenii were the dominant fungal species. Among the 5 ecotopes, samples from the ecotope located in the western region of the plateau with the harshest environment (altitude 4591–4977 m) had the lowest relative abundance of L. delbrueckii but the highest S. salivarius and S. thermophiles. In brief, the present study provides important information on an overview of the microbial resources in the traditional fermented yak milk from the Qinghai-Tibetan plateau, and the ecological regions had a remarkable influence on the microbial compositions in the traditional fermented yak milk.

Products of Lactobacillus delbrueckii subsp. bulgaricus Strain F17 and Leuconostoc lactis Strain H52 Are Biopreservatives for Improving Postharvest Quality of 'Red Globe' Grapes.

‘Red Globe’ table grapes are large, edible, seeded fruit with firm flesh that tastes good, but can have poor postharvest shelf-life. This study was conducted to explore the effects of products of Lactobacillus delbrueckii subsp. bulgaricus strain F17 and Leuconostoc lactis strain H52 on ‘Red Globe’ table grapes for the enhancement of shelf-life and improvement of grape quality characteristics during postharvest storage. Strains F17 and H52 were isolated from traditional fermented yak milk obtained in the Qinghai–Tibetan Plateau. Samples from untreated and treated grapes were analyzed for physicochemical, biochemical, and microbiological properties (weight loss, decay rate, pH, total soluble solids content, titratable acidity, total phenols, sensory evaluation, and microbial growth) for 20 days. The results demonstrated that supernatants from both strains significantly reduced weight loss, decay rate, aerobic mesophilic bacteria, and coliform bacteria counts; delayed maturity and senescence of table grapes; and reduced titratable acidity and total phenols. However, the supernatant of strain F17 was more effective and resulted in better sensory evaluations and had a significant inhibitory effect on yeast and molds by day 5. Meanwhile, the supernatant from strain H52 had a significant inhibitory effect on fungi over the whole storage period. In addition, the results of the Pearson correlation analysis suggested that weight loss, decay rate, total soluble solids content, and microorganisms were highly correlated with the sensory evaluation data and quality of postharvest grapes when treated with the products of strain F17. On the basis of these data and sensory organoleptic qualities, the supernatant containing products from strain F17 had the best potential as a biopreservative to improve the postharvest quality of ‘Red Globe’ table grapes.

Influence of a cholesterol-lowering strain Lactobacillus plantarum LP3 isolated from traditional fermented yak milk on gut bacterial microbiota and metabolome of rats fed with a high-fat diet.

L. plantarum LP3 isolated from traditinal fermented Tibetan yak milk has been identified as a potential probiotic candidate strain with high cholesterol-lowering activity. In this study, thirty Sprague-Dawley (SD) rats were randomly divided into three groups, including normal diet (NC), high-fat diet (HC), and high-fat diet + L. plantarum LP3 (HLp). The effects of L. plantarum LP3 on plasma lipid profile, gut bacterial microbiota, and metabolome induced by high-fat diet in rats were investigated. Results shown that L. plantarum LP3 administration was found to reduce the levels of total cholesterol, triglyceride, and low-density lipoprotein cholesterol (LDL-C) and atherogenic index in the serum of high-fat diet rats. It also controlled the decrease of Bacteroidetes and increase of Firmicutes at the phylum level in gut microbiota induced by high-fat diet in SD rats and increased the diversity and relative abundance of intestinal flora in obese rats. In particular, the LP3 strain controlled the changes induced by the high-fat diet in the abundance of for Lachnospiraceae and Erysipelotrichaceae. We also further observed the beneficial regulatory effects of L. plantarum LP3 on changes in the levels of obesity-related metabolites. The biosynthesis of fatty acids, steroids, and bile acids and metabolism of linoleic acid, linolenic acid, and arachidonic acid were the main metabolic pathways adjusted by L. plantarum LP3 in obese rats, and the metabolic rates were similar to those observed in normal diet rats levels. The findings of this study provided useful information on the mechanism underlying the hypocholesterolemic effects of L. plantarum LP3 in the high-fat induced SD rat model with the perspective of modulation of gut microbiota and metabolites.

Characteristics of volatile flavor components in traditional fermented yak milk produced in different ecoregions of the Qinghai-Tibetan plateau

The volatile flavor substances in traditional fermented yak milk samples collected from 5 ecoregions (A: coniferous forests and grasslands of the Qilian Qingdong Mountains; B: alpine grasslands surrounding the lakes in the Qiangtang Plateau; C: alpine shrubs and meadows of the Guoluo-Nagqu Highlands; D: coniferous forests along the alpine valley in East Tibet; E: shrubs and grasslands along the alpine valley in South Tibet) of the Qinghai-Tibetan plateau were comparatively analyzed. The relative percentage composition of volatile flavor substances varied among the different ecoregions. In samples collected from region E, more than 50% of the volatile flavor compounds were esters comprising mainly n-butyl acetate, butyl butyrate, and ethyl octanoate, and a considerable proportion of acetoin was found in samples from regions B and E. Greater proportions of 2-heptanone and 2-nonanone were observed in samples collected from regions A, C, and D compared with regions B and E.

Microbial diversity and volatile profile of traditional fermented yak milk

Previous research reported that fermented yak milk had a diverse microbial composition. For this study, raw yak milk, qula, and fermented yak milk samples were collected from the Aba Tibetan autonomous region of China. The genus and species microbial composition of these samples were analyzed by high-throughput sequencing of 16S rRNA and groEL gene amplicons, and the volatile profile of the samples was quantified by gas chromatography-mass spectrometry. The results indicated variation in abundance of microbiota at the genus level among the fermented yak milk samples, with Lactobacillus as the most abundant genus in the majority of samples, ranging from 41.6 to 98.3%. The volatile profile of the samples varied among those collected from different villages. Correlations between bacterial composition and volatile compounds of the samples were also observed. Lactobacillus displayed a significant correlation with volatile compounds such as benzaldehyde, 2,3-pentanedione, ethanol, and ethyl acetate, whereas the samples with relatively high abundance of Streptococcus and Lactococcus displayed relatively low contents of volatile compounds.

Physical and Chemical Composition of Traditional Fermented Yak Milk in Yangbajing Area

Physical and Chemical Composition of Traditional Fermented Yak Milk in Yangbajing Area

Predominant lactic acid bacteria in traditional fermented yak milk products in the Sichuan Province of China

摘要 : 中国四川地区的牦牛乳资源丰富,当地牧民生产和销售传统发酵牦牛乳制品已经有几百年的历史,其中蕴藏着的复杂微生物区系赋予牦牛乳制品独特的组织形态、风味和功能等品质特征。本研究通过纯培养的方式对从四川省不同牧民家庭采集的64份牦牛乳制品(酸牦牛乳,曲拉,鲜牦牛乳,乳清和奶油)中的乳酸菌进行分离,并通过形态观察、16S rDNA序列分析、种特异性PCR及tuf-PCR-RFLP等技术对其进行准确地鉴定,最终获得乳酸菌213株。结果表明这些传统乳制品中蕴含着丰富的乳酸菌资源,所获得的乳酸菌属于6个属17个不同种和亚种。6个属的分布如下:明串珠菌属占总分离株数的40.8%,乳杆菌属占39.0%,链球菌属占13.2%,乳球菌属占5.6%,肠球菌属占0.94%和魏斯特菌属占0.46%。其中,肠膜明串珠菌肠膜亚种 (61株,约占总分离株的28.6%) 和瑞士乳杆菌(41株,约占总分离株的 19.2%)是牦牛乳制品中所有乳酸菌分离株的优势菌群。本文系统地研究了中国四川地区各种牦牛乳制品中乳酸菌的组成,为益生菌和发酵剂的筛选提供了宝贵的资源,同时为工业化生产传统发酵乳制品的发酵剂的设计提供了基础数据。

Identification of lactic acid bacteria in traditional fermented yak milk and evaluation of their application in fermented milk products

In this study, 53 strains of lactic acid bacteria (LAB) isolated from Xueo, a traditional fermented yak milk in the western Sichuan Plateau of China, were identified and their use in fermented milk was evaluated. All gram-positive and catalase-negative strains were divided into 6 groups at the level of 87% similarity using amplified ribosomal DNA restriction analysis. These groups were identified as 6 species using 16S rDNA sequence analysis and atpA gene analysis. The dominant LAB strains in Xueo were Enterococcus durans, Lactobacillus fermentum, and Lactobacillus paracasei, accounting for 45.3, 22.6, and 17.0% of isolates, respectively. Milk fermented with most of the representative strains was high in quality, exhibiting relatively high viscosity, moderate acidity, good sensory quality, and high counts of viable LAB. Fermented milk of E. durans SCA16 and L. fermentum SCA52 achieved the highest scores for overall sensory quality. Most strains displayed antimicrobial activity against at least 1 of 9 spoilage microorganisms. Lactic acid was the main factor inhibiting the growth of spoilage bacteria, and H2O2 was also inhibitory to some extent. Excluding the influence of acid and H2O2, strains SCA52 (L. fermentum) and SCA7 (Lactobacillus plantarum) were antagonistic against some of the indicators, suggesting that the 2 strains may produce a bacteriocin-like substance. Therefore, the development of superior strains isolated from Xueo to ferment milk with similar flavor and texture to Xueo is expected.

Isolation and identification of cultivable lactic acid bacteria in traditional yak milk products of Gansu Province in China

Various traditional fermented yak milk and raw milk foods could be considered as an abundant resource for obtaining novel lactic acid bacteria (LAB) with unique properties. Eighty-eight samples of yak milk products were collected from Gansu Province in China. Three hundred and nineteen strains of LAB isolated from these samples were identified by phenotypic methods, 16S rRNA gene sequence analysis and PCR-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) technology. Among the isolates, one hundred and sixty-four isolates (51.41% of the total) were classified under Lactobacilli, and one hundred and fifty-five (48.59%) belonged to cocci. All the isolates were classified to six genera (Lactobacillus, Lactococcus, Leuconostoc, Streptococcus, Enterococcus and Weissella) and twenty-one species. Lactobacillus helveticus (87 strains), Leuconostoc mesenteroides subsp. mesenteroides (49 strains), Streptococcus thermophilus (39 strains), Lactobacillus casei (31 strains) and Lactococcus lactis subsp. lactis (19 strains) were considered as the predominant populations in the yak milk products. The results showed that there were abundant genus and species LAB existing in yak milk products in Gansu Province in China. The obtained LAB pure cultures may be a valuable source for further starter selection.

Safety evaluation in vitro of Enterococcus durans from Tibetan traditional fermented yak milk

Despite its ubiquity in fermented dairy products, the safety of lactic acid enterococcal bacteria remains controversial. In this study, five Enterococcus durans strains - A1, A2, B1, B2, and C1 - were isolated from traditional fermented yak milk from Tibet. To evaluate the strains' safety, biogenic amine production, antibiotic resistance and presence of known virulence determinants were investigated. Strain A1 can produce biogenic amines for histamine, spermine, and spermidine (mean values: 8.64, 8.31, and 0.30 mg/L, respectively). Polymerase chain reaction amplification for Strain A1 found genes involved in expression of gelatinase (gleE), cytolysin (cylA, cylB, and cylM), sex pheromones (ccf and cpd) and cell wall adhesion (efaA). Strain A2 showed sensitivity or intermediate resistance to all tested antibiotics, and no virulence determinants except gelE and ccf, but did produce tyramine at a relatively high level (912.02 mg/L). Both strains B1 and B2 could produce histamine (10.43 and 10.56 mg/L, respectively), and showed vancomycin resistance; B1 also produced tyramine (504.02 mg/L). Strain C1 could produce all five biogenic amines tested in the study -putrescine, histamine, tyramine, spermine, and spermidine; concentrations were 6.51, 9.59, 205.85, 5.55, and 5.39 mg/L, respectively. All E. durans strains found in Tibetan traditional fermented yak milk thus offer potential risk.

Comparison of nutrition and microbiological compositions between two types of fermented milk from Tibet in China

Twenty-nine traditional fermented yak milk (kurut) and 15 traditional fermented Mongolian cow milk (FMCM) samples were collected from three regions of Tibet in China, and their chemical composition and microbiological properties were analyzed. Average levels of the major composition of kurut and FMCM, respectively, were as follows: total solid, 16.91±1.30 g/100 g and 12.65±1.14 g/100 g; fat, 6.83±1.18 g/100 g and 3.92±0.92 g/100 g; total protein, 4.93±0.36 g/100 g and 3.33±0.71 g/100 g; free amino acid, 8.57±3.22 mmol/l and 2.23±0.62 mmol/l; calcamin, 117.26±9.66 mg/100 g and 86.51±7.55 mg/100 g; and phosphorus, 109.28±7.97 mg/100 g and 78.86±6.99 mg/100 g. The average bacteria count of lactic acid bacteria in kurut and FMCM were 7.66±0.71 and 8.03±0.68 log colony-forming units (cfu)/ml, respectively. Moreover, the average yeast counts of these two samples were 6.48±0.81 and 5.92±0.52 log cfu/ml, respectively. The result showed that the major nutritional composition content of kurut was significantly higher than that of FMCM, which indicated that kurut can be considered an invaluable fermentation product for human being.