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Yak milk is a valuable raw material for the production of functional food. Investigation of the fermentation process with commercial starter cultures is conducted to find suitable starters for producing fermented yak milk products on an industrial scale using modern rheological, microbiological, and sensorial methods. According to the acidification curve and rheological measurement, the gel-forming time of yak milk with mesophilic, thermophilic and mixed (meso-thermophilic) starter cultures was not significantly different from cow milk; but, yak milk had a significantly higher gel strength in all cases. The viable bacteria count of fermented samples with thermophilic starters was 8.23 log CFU·mL-1 for cow milk and 9.12 log CFU·mL-1 for yak milk. During cold storage (72 h), the CFU in yak milk remained higher (98.48% - 101.22%) during the storage period than that of cow milk (90.33% - 95.06%). The sensorial property scores of yak milk fermented with mixed starters were the highest, followed by those of milk fermented with mesophilic and thermophilic starter cultures. The obtained parameters show that mesophilic and mixed cultures are advantageous in terms of sensorial and probiotic properties, and thermophilic culture - in terms of gel strength. All this information is useful for the development of new dairy products. [ABSTRACT FROM AUTHOR]

The Ca2+-selective epithelial channel TRPV5 plays a significant role in renal calcium reabsorption and improving osteoporosis (OP). In this study, we investigated the mechanisms of yak milk on osteoporosis mice in TRPV5-mediated Ca2+ reabsorption in the kidney. We observed that treatment of OP mice with yak milk reconstructed bone homeostasis demonstrated by increasing the levels of OPG as well as decreasing the levels of TRAP and ALP in serum. Additionally, yak milk reduced the level of parathyroid hormone (PTH) and elevated 1,25-(OH) 2 D 3 and calcitonin (CT), and inhibited the excretion of Ca/Cr and Pi/Cr in OP mice, which explained by regulating hormone levels and thus enhance the renal Ca2+ reabsorption. Further analysis exhibited that yak milk upregulated the expression of TRPV5 protein and mRNA as well as calbindin-D 28k in OP mice kidneys. Overall, these outcomes demonstrate that yak milk enhances renal Ca2+ reabsorption through the TRPV5 pathway synergistically with calbindin-D 28k , thus ameliorating OP mice. This provides a new perspective for yak milk as a nutritional supplement to prevent osteoporosis. [Display omitted] [ABSTRACT FROM AUTHOR]

Yak milk is rich in essential milk proteins of nutritional and therapeutic value. In this study, whey proteins of milk from 3 yak breeds (Gannan, GN; Huanhu, HH; Maiwa, MW) in China were comprehensively identified and compared using a data-independent acquisition quantitative proteomics approach. A total of 632 proteins were identified in yak milk whey samples, in which immune-related proteins were abundant. Compared with other milks, more proteins were involved in oxidation-reduction process and with ATP binding. In addition, we identified 96, 155, and 164 differentially expressed proteins (DEP) for GN versus HH, GN versus MW, and HH versus MW, respectively. "Phagosome" and "complement and coagulation cascades" were the most significant pathways for DEP of GN versus HH and GN or HH versus MW yak milk based on the Kyoto Encyclopedia of Genes and Genomes pathway analysis. Protein-protein interaction network analysis showed that DEP for the 3 comparisons had significant biological interactions but were associated with different functions. The results provide useful information on yak milk from different breeds in China, and elucidate the biological functions of yak milk proteins. [ABSTRACT FROM AUTHOR]

The effect of milk on bone health is controversial. In this study, the effects of yak milk in mice with retinoic acid-induced osteoporosis (OP) were evaluated. Yak milk was provided to OP mice as a nutrition supplement for 6 wk. The results showed that yak milk significantly reduced bone turnover markers (tartrate acid phosphatase and alkaline phosphatase). The yak milk treatment was also associated with remarkably increased bone mineral density, bone volume, trabecular thickness, and trabecular number, as well as improved biomechanical properties (maximum load and stress) of the tibia. Furthermore, yak milk mitigated the deterioration of the network and thickness of trabecular bone in treated OP mice compared with the OP model group. The results indicated that yak milk could improve bone mass and microarchitecture through the inhibition of bone resorption in OP mice. [ABSTRACT FROM AUTHOR]

This study aimed to reveal the change patterns of the phosphorylation modification status of yak whey phosphoproteins during lactation and their physiological effects. Herein, we comprehensively characterized whey phosphoproteome in yak colostrum and mature milk using an ultra-high throughput phosphoproteomics approach incorporating trapped ion mobility technology. A total of 344 phosphorylation sites from 206 phosphoproteins were identified, with individual site modification predominating. Notably, 117 significantly different phosphorylation sites were distributed on 89 whey phosphoproteins. Gene ontology analysis indicated that these significantly different whey phosphoproteins (SDWPPs) were mainly annotated to carbohydrate metabolic process, membrane, extracellular region and calcium ion binding. Metabolic pathway enrichment analysis demonstrated that SDWPPs were critically involved in protein processing in endoplasmic reticulum, NOD-like receptor signaling pathway and N-glycan biosynthesis. Our results elucidate the phosphorylation profiles of yak whey phosphoproteins at different lactations and their adaptive regulatory role in meeting the nutritional requirements of yak calves during development. [Display omitted] • Differences in whey phosphoproteins in yak colostrum and mature milk were revealed. • A total of 344 phosphorylation sites on 206 whey phosphoproteins were identified. • 117 phosphorylation sites on 89 whey phosphoproteins were differentially regulated. • Beta-lactoglobulin and lactoperoxidase were first characterized as phosphoproteins. • Phosphorylation may regulate the function of whey phosphoproteins during lactation. [ABSTRACT FROM AUTHOR]

The gold standard of milk is human milk, not cow milk. The present study expects to explored the comprehensive nutritional value of different kinds of milk and the differences between them through multi-omics analysis and found functional components that are more similar to human milk. This study employed untargeted LC-MS/MS metabolomics, untargeted LC-MS/MS lipidomics, and 4D label-free proteomics analysis techniques. The findings revealed substantial disparities in metabolites, lipids, and proteins among the five types of milk. Notably, pig milk exhibited a remarkable abundance of N -acetylneuraminic acid (Neu5Ac) and specific polar lipids. Yak milk stood out with significantly elevated levels of creatine and lipoprotein lipase (LPL) compared to other species. Buffalo milk boasted the highest concentrations of L-isoleucine, echinocystic acid, and alkaline phosphatase, tissue-nonspecific isozyme (ALPL). The concentrations of iminostilbene and osteopontin (OPN) were higher in cow milk. • In this study, 4D-Label-Free proteomics technique was used. • Neu5Ac and specific polar lipids are significantly present in YXP. • Creatine and LPL are important nutrients in QHY. • In GXB, L-isoleucine and echinocystic acid are key nutrients. • Iminostilbene and OPN have significant advantages in HST. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lipid differences between yak colostrum (YC) and mature milk (YM) were analyzed. • A total of 851 lipid species from 28 lipid subclasses were identified. • Forty-three significantly different lipids (SDLs) between YC and YM were screened. • These SDLs were mainly enriched in the glycerophospholipid metabolic pathway. • Lipid species information for GLs, STs, GPs, SPs, and FAs in YC and YM was added. Yak milk is essential to maintain the normal physiological functions of herders in Tibetan areas of China. However, the lipid components of yak colostrum (YC) and mature milk (YM) have not been systematically studied. We employed a quantitative lipidomics to comprehensively describe the alterations in the milk lipid profile of lactating yaks. Herein, totally 851 lipids from 28 lipid subclasses in YC and YM were identified and screened for 43 significantly different lipids (SDLs; variable importance in projection > 1, fold change < 0.5 or > 2 with P < 0.05), with cholesterol ester (CE, 16:0) and triacylglycerol (TAG, 54:6 (20:5), 50:1 (16:0), 56:6 (20:5)) were the potential lipid biomarkers. Fourteen SDLs were modulated downwards, and 29 SDLs were modulated upwards in YM. Moreover, by analyzing lipid metabolic pathways in these SDLs, glycerophospholipid metabolism was the most critical. Our results furnish integral lipid details for evaluating yak milk's nutritional quality. [ABSTRACT FROM AUTHOR]

Based on CNKI, the article uses CiteSpace V software to analyze 460 literatures related to yak milk in China from 1992 to 2020, draw knowledge maps such as authors, institutions, keywords and so on, to explore the relationship between yak milk development research institutions, research hotspots and future development trends. The results show that the research scholars and institutions related to yak milk have carried out relatively close cooperation and exchanges, and formed cooperative groups in the region. The specific manifestation was that there are academic exchanges on yak milk in Gansu Research Center, but there is less cooperation with other high-yield institutions. Before 2015, the research hotspots were mainly white yak milk, milk protein, etc. After 2015, the research hotspots turned to casein, hard cheese, etc. Among them, the processing of dairy products such as hard cheese becomes a continuous research frontier hotspot. Therefore, yak milk research is changing from yak milk nutritional components, efficacy and other aspects to yak milk product processing and other aspects. Relying on the strength of science and technology, developing traditional dairy products into functional and characteristic products, and making use of product advantages to create high-end brands will become an important direction for the research and development of yak milk. [ABSTRACT FROM AUTHOR]

Yak milk is an essential and predominant food resource for Tibetan people for subsistence purposes and to combat altitude-induced challenges. Due to its unique qualities, yak milk has recently been gaining broader attention from consumers across China as well in other parts of the world. One of the key characteristics of yak milk is the protein content, which is about 40 to 60% higher than that of native bovine milk. In this work, a sensitive and reproducible high-throughput analytical method was developed employing both ultra high-performance liquid chromatography Orbitrap (Thermo Fisher Scientific) high-resolution accurate mass spectroscopy (UHPLC-HRAM-MS) and UHPLC coupled with triple quadrupole tandem MS (UHPLC-QqQ-MS) to simultaneously analyze 8 milk proteins. A total of 15 Maiwa yak milk samples and 15 bovine milk samples were qualitatively and quantitatively analyzed using targeted proteomics and compared for α-lactalbumin, β-lactoglobulin, α S1 -casein, α S2 -casein, β-casein, κ-casein, lactoferrin, and osteopontin. Peptides of β-lactoglobulin were used to specifically distinguish yak and bovine milk. The results showed that this novel detection method could quantitatively detect these major and minor milk proteins with >0.99 linear correlation coefficient and a recovery rate between 90 and 120%, with relative standard deviations typically less than 10%. The data revealed that yak milk not only had higher overall milk protein content than bovine milk but higher lactoferrin and osteopontin contents as well. The lactoferrin content of yak milk was about 30% higher than that of bovine milk, and the osteopontin content of yak milk was nearly twice that of bovine milk. The application of this method demonstrates that UHPLC-HRAM-MS and UHPLC-QqQ-MS are suitable for high-throughput qualitative and quantitative analysis of major and minor proteins of yak and bovine milk. [ABSTRACT FROM AUTHOR]

This study aims at investigating whether the livestock, lactation stage, or geographical origin of specialty milk in China could be classified by the elemental contents. Samples of goat, buffalo, and yak milk were collected from main production provinces in China and the contents of nine elements in milk from different livestock, regions, and lactation stages were determined. Statistical analysis indicated that the contents of Mn, Cu, As, Se, Cs, and Mo in mature milk were significantly different between the three livestock (p < 0.05). The trends of Mn and Cs contents of the goat milk and buffalo milk increased first and then decreased gradually during lactation. The contents of Se, Cs, Ba, and Mo in mature milk of three livestock were significantly different between the three regions (p < 0.05). The result of linear discriminant analysis (LDA) and partial least squares discrimination analysis (PLS‐DA) showed that the total correct classification rates in different livestock for mature milk reached 86.7 and 90%. For goat milk, the total correct classification rates of different lactations and regions reached 88.9 and 77.8% for LDA (100 and 87.5% for PLS‐DA), and followed by yak milk of different regions which achieved 88.9% for LDA (88.9% for PLS‐DA). In summary, the microelements in milk showed a significant correlation with livestock, region, and lactation of goat, buffalo, and yak milk. The elemental fingerprints combined with the LDA could be potential for classifying the livestock, lactation stage, and geographical origin of milk. Practical Application: According to study the contents of miroelements in milk from different livestock, regions, and lactation stages, provide evidence and support for classifying the livestock, lactation stage, and geographical origin of milk. [ABSTRACT FROM AUTHOR]

α-Lactalbumin (α-LA) and β-lactoglobulin (β-LG) were isolated from yak milk and identified by mass spectrometry. The variant of α-LA (L8IIC8) in yak milk had 123 amino acids, and the sequence differed from α-LA from bovine milk. The amino acid at site 71 was Asn (N) in domestic yak milk, but Asp (D) in bovine and wild yak milk sequences. Yak β-LG had 2 variants, β-LG A (P02754) and β-LG E (L8J1Z0). Both domestic yak and wild yak milk contained β-LG E, but it was absent in bovine milk. The amino acid at site 158 of β-Lg E was Gly (G) in yak but Glu (E) in bovine. The yak α-LA and β-LG secondary structures were slightly different from those in bovine milk. The denaturation temperatures of yak α-LA and β-LG were 52.1°C and 80.9°C, respectively. This study provides insights relevant to food functionality, food safety control, and the biological properties of yak milk products. [ABSTRACT FROM AUTHOR]

BACKGROUND Yak milk formed stronger rennet‐induced gels if the milk contained smalled casein micelles and a higher concentration of calcium. Also casein gels could formed after a shorter incubation time if the milk contained smalled casein micelles. The objective of this study was to estimate the importance of yak casein micelle size on rennet‐induced coagulation properties. RESULTS: Three fractions of different‐sized, undamaged casein micelles (Ф112.17 ± 0.83 nm, Ф207.13 ± 0.59 nm and Ф269.37 ± 2.89 nm) were obtained by ultracentrifugation. The smallest casein micelles had the highest concentrations of calcium (803.21 ± 8.49 mM), phosphate (445.52 ± 10.66 mM), and κ‐casein/total casein (19.45%). Rheological analyses determined the optimal gelation times of small, medium, and large casein micelles to be 9.5 ± 0.5, 10.8 ± 0.5, and 13.3 ± 0.2 min, respectively. Higher κ‐casein concentration in the small casein micelles appeared to facilitate their shorter incubation time. Both the faster caseinomacropeptide (CMP) release rate and rennet‐induced aggregation rate of small casein micelles contributed to a faster change in turbidity. Furthermore, small casein micelles had the highest elastic modulus (G′, 73.21 ± 4.5 Pa) 60 min after the addition of rennet. This was consistent with micro‐photographs, which showed that small casein micelles could form a more homogeneous gel, which had smaller pore sizes. Trial cheese manufacture verified that yak cheese containing small casein micelles, formed curd faster and the cheese had higher texture profile analysis (TPA) values for hardness, cohesiveness, and springiness. CONCLUSION: This is important information for the optimization of yak cheese industrial production. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Yak is one of the few species of which the rennet-coagulated cheese making characteristics of its milk are still not well understood. This study investigated composition and rennet-induced coagulation properties of milk from 17 individual yak cows in comparison with milk from 32 individual Holstein cows. Yak cows produced milk with generally higher concentrations of milk components. The concentrations of fat, protein, solids-not-fat (SNF), and calcium in yak milk were 1.89-, 1.68-, 1.46-, and 2-fold those in Holstein milk, respectively. The hydrodynamic radii of casein micelles (187.25 nm) and chymosin-induced paracasein (1,620 nm) were about twice the sizes of those found in Holstein milk. Higher concentrations of calcium in yak milk, together with larger sizes of casein micelles, explains the reason for its fast rate of curd formation and firmer curd texture. Optical microrheology analysis also showed that Ca2+ concentration had greater influence on the coagulation of yak milk than on Holstein milk. Cheese making trials with yak and Holstein milk proved the higher cheese yield of yak milk: 1.67-fold that of Holstein milk. Therefore, yak milk could be a suitable source of milk for enzyme-coagulated cheese making. [ABSTRACT FROM AUTHOR]

Amplification-based nucleic acid testing has become a widely used method for food authenticity analysis. However, due to the need for specialized instrumentation, technical expertize, and trained operators, routine nucleic acid analysis can only be performed in a laboratory setting. For perishable products like yak milk, rapid and accurate detection of dairy components on-site is crucial for the automated management of the production process and improving the milk's quality at dairies. As a feasibility study, we developed an assay strategy for the simultaneous qualitative detection of yak and cow derived components in yak milk. We presented a handheld integrated cassette that combined rapid extraction and purification of dairy nucleic acids, loop-mediated isothermal amplification (LAMP), and visual detection of lateral flow strips (LFS). To enable visual detection of LAMP amplification products on LFS, we utilized a unique primer modification method that labeled the amplification terminator and single oligonucleotide sequence at the 5′ end of the loop primer. This modification avoids the use of antibodies and conventional fluorescein/biotin. The cassette allowed for DNA transfer, fluid drive, and liquid mixing by magnetic force and gravity alone, without the need for complex pumps and valves. The disposable cassette is easy to use, costs less than $1 to produce, has low instrument dependency, and is well suited to on-site detection. The platform can detect 0.1% of cow milk adulteration in yak milk within 50 min. This fully integrated "sample in-result out" detection procedure can also be extended to other detection areas. [Display omitted] • On-site nucleic acid analysis is critical for perishable products. • A handheld cassette combines rapid extraction, amplification, and visual detection. • Modified primers enable visual detection without antigen/antibodies. • The cassette is low-cost, easy to use, and suitable for on-site detection. • The method detects 0.1% of cow milk adulteration in yak milk within 50 min. [ABSTRACT FROM AUTHOR]

To facilitate development of new yak milk products with high added value, sterilization effects of direct steam injection (DSI) were evaluated. The Z value (temperature increase necessary to reduce inactivation time by 90%) of Geobacillus stearothermophilus spores (ATCC 7953; 106 CFU mL−1) in yak milk was 5.88 °C. Heating of the milk above 153.86 °C for 0.116 s achieved complete inactivation of ATCC 7953 spores; i.e., commercially-acceptable sterility. The native lactoferrin and β-lactoglobulin (β-Lg) contents of the milk decreased by 40 and 30% after DSI treatment, respectively, whereas the α-lactalbumin (α-La) content did not differ significantly; the overall extent of denaturation of heat sensitive proteins was lower than in UHT milk. The furosine and lactulose contents in DSI treated yak milk were ≤1.11 mg/10 g of protein and 0.368 mg/10 mL, respectively, similar to those in pasteurized milk. The pH, Hunter color values and aroma were significantly influenced by DSI treatment, but the overall sensory acceptability of DSI treated yak milk was assessed as good. These findings indicate that DSI has great potential for producing yak milk and processed yak milk products with considerable added value. • DSI achieved a 3-log reduction of ATCC 7953 spores in yak's milk at 154 °C for 0.116 s. • DSI reduces the denaturation of heat sensitive serum proteins in yak's milk. • DSI has potential to produce high added value yak's milk. [ABSTRACT FROM AUTHOR]

• Yak milk is rich in flavor components and is mostly in trace levels. • DHS method allowed a green, high throughput and efficient sample extraction. • Analytical method was developed and validated by chemometrics. • An external standard provided more accurate quantitative. • The CAR/PDMS/DVB material provided the best extraction of volatiles from yak milk. A dynamic headspace (DHS) with DVB/CAR/PDMS trapping materials was coupled to a gas chromatography-mass spectrometry for the separation and identification of volatile-flavor compounds in bos grunniens (yak) milk. The principal components analysis coupled with response surface methodology optimized the main variables of the device (10 g sample quality, 5 min desorption time, 3.0 g adding sodium chloride, 72 °C extraction temperature, 28 min pre-equilibrium time and 86 min extraction time). Total 235 volatile components were identified. The limit of detections and quantifications of volatile components were 0.01–5.35 mg kg−1 and 0.01–9.41 mg kg−1, respectively, with relative standard deviation from 0.2% to 6.4%. The method performed well during volatile-flavor components analysis from the yak milk sample, producing excellent extraction parameters for the volatile components. Eighty-two volatile components identified in yak milk belonged to a broad range of chemical classes (ketones, aldehydes, aromatics, acids, alkanes, and estes), and 73 of them were at trace levels. Meanwhile, using gas chromatography-olfactometry technique, 11 volatile components were identified as contributors to the aroma of yak milk. In conclusions, a sensitive, convenient and reliable method was developed for the accurate determination of volatile-flavor compounds in yak milk utilizing DHS-GC/MS analyses. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the importance and effects of age, hair color, lactation stage and number of yak, as well as physicochemical properties and composition of yak milk on rennet-induced coagulation characteristics. Results showed that casein micelle size distribution and total calcium content of milk from 68 yaks were the most important factors affecting the gelation characteristics, including gelling time and gel strength. The yak milk containing smaller casein micelles and higher calcium content formed stronger gels and had shorter incubation time. Moreover, casein micelle samples containing 20.6, 16.8, and 13.9 mmol/L micellar calcium were obtained through pH-induced dialysis method. The results clearly showed that although the removal of micellar calcium did not affect casein macropeptide (CMP) release, the gelation of samples containing lower micellar calcium value corresponded to lower aggregation rate of para -casein micelles and more CMP release. In addition, removal of micellar calcium may lead to longer incubation time and sparser gel structure. This study highlights that higher micellar calcium is indispensable to the aggregation of yak casein micelles and the formation of firm gel, because enough micellar calcium may promote the aggregation of para -casein and firmly links casein micelles. Image 1 • Micelle size and calcium content are the most important factors affecting gelation characteristics. • Higher micellar calcium is indispensable to aggregation of yak milk casein micelles. • Removal of yak milk micellar calcium do not affect release of casein macropeptide. • Micellar calcium promotes aggregation of para -casein and firmly links casein micelles. [ABSTRACT FROM AUTHOR]

Yak milk fat products constitute the base of Qinghai-Tibetan pastoralists’ daily food intake. Despite the great importance of fat in processing and pastoralists’ health, studies about yak milk fat are scarce. In this study, the lipid composition and the morphological properties of milk fat globule membranes (MFGMs) of yak milk were investigated. The results demonstrated that the yak milk had a higher cholesterol and sphingomyelin content compared to cow milk. In situ structural investigations performed at 25 °C by confocal microscopy showed the presence of lipid domains in yak MFGM, with a larger number and wider size range compared to cow milk. Moreover, the simultaneous localization of glycosylated molecules and polar lipids indicated that glycosylated molecules could be integrated into the lipid domains in yak MFGM. Different characteristics in yak MFGM could be related to the lipid composition and may affect the functions of yak milk lipids during processing and digestion. [ABSTRACT FROM AUTHOR]

The dissociation of yak casein (CN) micelles was evaluated by scanning electron microscopy, particle size, fluorescence properties, and soluble mineral and CN molecule content at pH 4.6 to 8.2. The results showed that the size of CN micelles remained constant with decreasing pH from 8.2 to 5.8 but sharply increased at pH ≤5.4. Casein micelles began to aggregate at pH 5.4, and the serum magnesium, potassium, iron, zinc, copper, and manganese levels had their minimum values at this pH level. During acidification, colloidal calcium phosphate dramatically disassociated from yak CN micelles, but the soluble CN monomer content decreased slightly. During alkalization, the soluble calcium and phosphorus content decreased below pH 6.8 but increased with pH increases from 6.8 to 8.2. However, the soluble CN content increased markedly during alkalization. The emission wavelength of 8-anilino-1-naphthalenesulfonic acid sodium salt fluorescence decreased during both acidification and alkalization from pH 6.6, whereas the opposite was found for intrinsic fluorescence. [ABSTRACT FROM AUTHOR]

Yak butter is one of the most important foods for the Tibetan people. Of note, its production yields waste yak milk as a by-product. In this work, waste yak milk protein hydrolysates made via Pepsin hydrolysis were shown to have antimicrobial activity. Furthermore, an innovative method of magnetic liposome adsorption combined with reversed-phase high performance liquid chromatography (RP-HPLC) was developed to screen for and purify the antimicrobial peptides. Two antimicrobial peptides were obtained and their amino acid sequences were determined by N-sequencing, namely Arg-Val-Met-Phe-Lys-Trp-Ala and Lys-Val-Ile-Ser-Met-Ile. The antimicrobial activity spectra of Arg-Val-Met-Phe-Lys-Trp-Ala included Bacillus subtilis, Staphylcoccus aureus, Listeria innocua, Escherichia coli, Enterobacter cloacae and Salmonella paratyphi, while the Lys-Val-Ile-Ser-Met-Ile peptide shows not only bacterial growth inhibition but also of fungi. Haemolytic testing suggested that these two antimicrobial peptides could be considered to have no haemolytic effect at their minimum inhibitory concentrations (MICs). [ABSTRACT FROM AUTHOR]

A differential scanning calorimetry (DSC) method was used to investigate the denaturation temperature of yak α-lactalbumin (α-La), β-lactoglobulin (β-Lg), and a mixture of two proteins and the thermal properties of α-La and β-Lg in the presence of glucose, lactose, sucrose, NaCl, CaCl, and at various pH (4.0-10.0). The denaturation temperature ( T ) of α-La increased from 52.1 °C in the absence of β-Lg to 53.9 °C in the presence of β-Lg, while the T of β-Lg decreased from 81.4 °C in the absence of α-La to 79.9 °C in the presence of α-La. α-La was thermal stable in the range of pH 4.0-10.0, while β-Lg was more thermal stable in acidic pH than in alkaline pH. Sugars, Na, and Ca influenced the stabilization of the two proteins against thermal denaturation with greatly influenced for β-Lg. α-La kept reversibility in the presence of sugars, NaCl, CaCl, and over a wide pH range (4.0-10.0), with most of the reversibility values being greater than 90%. In contrast, β-Lg was completely irreversible whether in its native state or in the presence of the additives. [ABSTRACT FROM AUTHOR]

Probiotic industries strive for new, efficient and promising probiotic strains that impart a positive impact on consumer health. Challenges are persisting in isolation, screening, and selection of the new indigenous probiotic strains. In the present research, we explored the probiotic potential of 17 lactic acid bacteria isolated from Yak milk in a series of in vitro tests. We also demonstrated their health benefits, i.e., cholesterol degradation, lactose digestion, antimicrobial activity, antioxidant, and anticancer activities. Principal component analysis revealed that more than 50% of the strains fulfilled the examined criteria, e.g., survival in acidic pH, bile concentrations, and adherent property. Approximately all the strains produced antimicrobial substances against the maximum number of tested strains including clinical strains. Most strains degraded cholesterol in comparison to the reference probiotic strain whereas strain Yc showed 1.5 times higher the degradation efficiency of the control strain. Lan4 strain exhibited remarkable anticancer activity and induced the maximum apoptosis (87%) in the Hela cells and was non-toxic to the non-cancerous HEK293 cells. Around ten strains showed positive lactose digestion. Overall, this can be concluded that selected lactic acid bacteria revealed excellent probiotic properties along with desirable health benefits. These strains need to be further investigated in details for their application in the development of novel probiotic preparations for the improvement of public health. [ABSTRACT FROM AUTHOR]

[Display omitted] • Raw and heated yak milks were digested in a dynamic in vitro digestion system. • More structured clots were formed in the stomach for raw and autoclaved milks. • The autoclaved milk showed the lowest gastric emptying rate with the greatest t 1/2. • Protein digestibility followed the order of pasteurized milk > microwaved milk ≈ autoclaved milk > raw milk. • The formation of structured clots was crucial for gastric emptying and digestion kinetics of yak milk. Yak milk is highly nutritious in terms of abundant protein and fat, whereas little is known regarding the influence and mechanism of heat treatments on its gastric emptying and hydrolysis kinetics during digestion in the human gastrointestinal tract. In this study, a bionic human stomach-intestine system was employed to examine in vitro dynamic gastrointestinal digestion of fresh raw and heated yak milks. During gastric digestion, the formation of protein clots or aggregates was observed for all the milk samples. However, significantly more clots were found from autoclaved milk and raw milk, with a dry weight of 14.1 and 10.9 g from 200 g initial milk sample after 30 min digestion, respectively, compared to pasteurized (6.9 g) and microwaved (9.2 g) milks. For both raw and heated milks, the large-sized coalesced fat globules formed in the stomach were rapidly dissociated to small and uneven droplets upon digestion in the small intestinal conditions due to the highly efficient hydrolysis of milk fat globule membrane (MFGM) proteins and fat globules by pancreatic trypsin and lipase. Due to the formation of more dense-structured clots, a longer gastric emptying half-time was shown for the autoclaved (41.1 min) and raw (38.4 min) milks in comparison to that for the yak milks treated with microwave (34.2 min) and pasteurization (36.2 min). Consistently, the pasteurized milk (92.5 %) exhibited the highest protein digestibility at the end of digestion, followed by microwaved milk (87.8 %) ≈ autoclaved milk (86.1 %) > raw milk (80.8 %). The amount of free fatty acids (FFAs) released during digestion in general followed a similar order with that for proteolysis among the milk samples. This study highlights the crucial role of the formation of structured clots in the gastric emptying and hydrolysis of proteins and fat globules. This information will provide a mechanistic understanding of digestion kinetics of yak milk as impacted by heat treatments. [ABSTRACT FROM AUTHOR]

Two novel oligosaccharides were isolated from yak milk. The milk was processed by the method of Kobata and Ginsberg involving deproteination, centrifugation and lyophilization followed by gel filtrate chromatography acetylation and silica gel column chromatography of derivatized oligosaccharides while their homogeneity was confirmed by HPLC. The structures of these isolated oligosaccharides were elucidated by chemical transformation, chemical degradation, 1 H, 13 C NMR, 2D NMR (COSY, TOCSY and HSQC) and mass spectrometry. The geometry of compound A (Bosiose) and B (Bovisose) have been optimized at B3LYP method and 6-311 + G(d,p) basis set. The difference between the energies of A and B is 1.269 a.u. or 796.309 kcal/mol. [ABSTRACT FROM AUTHOR]

This work characterized a fraction of constituents in yak milk within the realm of approximately 1,000 to 3,000 Da using matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry. Eleven samples of yak milk powder from the Sichuan province of China were received by the Department of Food Science, University of Wisconsin-Madison, and stored at room temperature until analysis. Sample preparation involved delipidation and deproteinization of yak milk samples and cold ethanol precipitation. Subsequently, MALDI time-of-flight mass spectrometry was performed in positive ion, reflector mode (AB Sciex TOF/ TOF 4800 MALDI; AB Sciex, Foster City, CA). The instrument was first calibrated with the manufacturer's 6-peptide mixture, and each spectrum was internally calibrated using the accurate mass of ACTH Fragment 18-39 standard peptide (protonated mass at m/z 2464.199) present in each sample. Laser power was adjusted for the calibration standards and for each sample so that the signal obtained for the most-abundant ion in each spectrum could be maximized, or kept below ∼2 × 104 to preserve spectral quality. Structure and name based on mass were matched using the Metlin metabolite database (https://metlin.scripps.edu/index. php). Results of the current work for yak milk powder showed a large variety of sphingolipid structures with clusters around 1,200, 1,600, and 2,000 Da. The profiling matched several glycosphingolipids, such as gangliosides GA1, GD1a, GD1b, GD3, GM1, GM2, GM3, and GT2 and several other unique moieties, including deaminated neuraminic acid (KDN) oligosaccharides, and fucose containing gangliosides. Matrix preparation and MALDI time-of-flight parameters were important factors established in this work to allow high resolution profiling of complex sphingolipids in yak powder milk. [ABSTRACT FROM AUTHOR]

Serum heat-induced protein aggregates at various pH levels were isolated from heated yak milk by size-exclusion fast protein liquid chromatography. Analysis by reversed-phase high-performance liquid chromatography showed that β-lactoglobulin and κ-casein were the two main proteins in these aggregates. The amount of serum heat-induced protein aggregates increased from pH 6.6 to 7.4, whereas the content of β-lactoglobulin in aggregates decreased from 61.9% at pH 6.6 to 50.4% at pH 7.2, and then increased to 51.3% at pH 7.4. The content of κ-casein, αs1-casein and β-casein increased from pH 6.6 to pH 7.4. These results show that serum heat-induced protein aggregates are pH dependent. [ABSTRACT FROM AUTHOR]

In the current study, a simple, sensitive, and specific ELISA assay using a high-affinity anti-bovine β-casein monoclonal antibody was developed for the rapid detection of cow milk in adulterated yak milk. The developed ELISA was highly specific and could be applied to detect bovine β-casein (10--8,000 μg/mL) and cow milk (1:1,300 to 1:2 dilution) in yak milk. Cross-reactivity was <1% when tested against yak milk. The linear range of adulterant concentration was 1 to 80% (vol/vol) and the minimum detection limit was 1% (vol/vol) cow milk in yak milk. Different treatments, including heating, acidification, and rennet addition, did not interfere with the assay. Moreover, the results were highly reproducible (coefficient of variation <10%) and we detected no significant differences between known and estimated values. Therefore, this assay is appropriate for the routine analysis of yak milk adulterated with cow milk. [ABSTRACT FROM AUTHOR]

Abstract: In highland pastures, where no agricultural and industrial activities exist, organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) are believed to be mainly coming from water–soil–grass system which is subject to air–water and air–soil exchanges and atmospheric precipitation. Samples of grass and yak muscle, liver, and milk were measured for OCPs and PCBs in the summer and winter of 2011. The total concentrations of HCHs, DDTs, endosulfans, HCB, and PCBs in grass samples were in the range of 0.53–2.45, 1.6–6.0, 1.10–4.38, 0.30–1.24, 0.65–2.04ngg−1 dw (dry weight), with the means 1.38, 2.86, 2.06, 0.73, and 1.19ngg−1 dw, respectively. The mean concentrations of HCHs and DDTs in yak muscle were 1.65 and 0.55ngg−1 fw (fresh weight), respectively; no significant seasonal differences. The average total concentrations of HCHs, DDTs, HCB, endosulfans, and PCBs in yak milk were 4.46, 0.59, 1.00, 0.27, and 0.097ngg−1 fat, respectively. Among the POPs investigated, β-HCH and HCB were dominant in yak muscle and liver, whereas β-HCH dominated the yak milk. Consistent with the results of other studies, PCB 153, 138, and 180 were detected in yak milk that is in accordance with the case reported for farmed cow milk in China and other countries. A human health risk was conducted based on the intake of OCPs via consumptions of the yak muscle and milk. Since the daily intake of HCHs and DDTs was lower than WHO or USEPA's acceptable daily intake or minimal risk level, showing that the consumptions of the yak muscle and milk would not pose any immediate risk to local people. [Copyright &y& Elsevier]

Heat treatment is one of the essential operations widely used in most dairy processes, and heat stability is one of the essential properties of milk. Casein micelles are the major component in milk responsible for the heat stability of milk during processing. This study assessed the effects of heat treatment temperature and duration on the average size, turbidity, polydispersity index and heat stability of casein micelles in yak skim milk and distilled water. The results showed that whey protein had an important role in influencing the heat stability of casein micelles. The average size, polydispersity index and turbidity of micelles in skim milk were higher than those of micelles in distilled water in all cases while the heat stability of casein micelles in skim milk was lower than those in distilled water. As a result of the heat treatment, the size of micelles in skim milk increased due to complex of casein/whey protein formed via covalent bonds, whereas it decreased in distilled water attributed to the change of hydrophobicity in micelles. The size distribution of particles broadened with increasing heating temperature, resulting in the increase in turbidity and polydispersity index of casein micelles both in skim milk and distilled water. The micelles in skim milk combined with whey protein during heating. These findings will help processors design appropriate heating conditions for yak milk and yak casein products and help identify new opportunities for product development. [ABSTRACT FROM AUTHOR]

Tibetan nomads have lived since ancient times in the unique and harsh environment of the Qinghai-Tibetan Plateau with average altitudes over 4000 m. These people have been able to live and multiply healthily over numerous generations under the extreme stress of high-altitude environment, including cold, hypoxia, and strong ultraviolet radiation, and with a simple diet devoid of vegetables and fruits for most of the year. Their survival depends heavily on yak milk, and its products comprise the main portion of their daily diet. In this review, yak milk and its derived products are examined in detail and compared with milk from other ruminant species. Yak milk products seem to be particularly rich in functional and bioactive components, which may play a role in maintaining the health status of Tibetan nomads. This includes particular profiles of amino acids and fatty acids, and high levels of antioxidant vitamins, specific enzymes, and bacteria with probiotic activity (yoghurt is the main food). Based on that, it is proposed that the Tibetan nomads have developed a nutritional mechanism adapted to cope with the specific challenges posed by the environment of the world's highest plateau. Systematic studies are required to demonstrate this in a more mechanistic way. [ABSTRACT FROM AUTHOR]

Yak milk (YM) has higher protein content than other bovine milk (BM) varieties. The bioactivity of milk glycoproteins is related to N / O -glycans. We qualitatively and quantitatively compared the N / O -glycome of YM and BM glycoproteins using stable isotope labeling combined with hydrophilic interaction chromatography and electrospray ionization mass spectrometry. We identified 79 and 78 N -glycans in YM and BM, respectively. Two N -glycans (H4N5F1A1; H5N4F1) were exclusive to YM. The content ratios of different types of N -glycans differed significantly between YM and BM, with sialylated N -glycans 2.33 times more abundant in YM. Five and seven O -glycans were detected in YM and BM, respectively. Two O -glycans (H1N2; H1N2A1) were exclusive to BM. The bi-sialylated O -glycan, H1N1A2, accounted for 56.1% of O -glycans in YM; it was 5.97 times more abundant in YM than in BM (equal volume basis). This study provides a theoretical basis for the future utilization of YM as a functional food. [Display omitted] [ABSTRACT FROM AUTHOR]

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. • Microbial community in kurut from 5 ecotopes of the Tibetan plateau was studied. • The dominant bacterial species were L. delbrueckii , S. salivarius , S. thermophiles. • Saccharomyces cerevisiae was the most dominant fungal species in the kurut. • Samples from mild climate ecotope had lower bacterial but higher fungal diversity. • Samples from harsh climate ecotope had less L. delbrueckii but higher Streptococcus. [ABSTRACT FROM AUTHOR]

The growth-promoting effects of κ-casein hydrolysates produced by four different proteases (trypsin, alcalase, papain and chymosin) on bifidobacteria ( Bb12 and BBMN68) viability were evaluated. Results showed that the obtained κ-casein hydrolysates possessed better property for improving the viability of Bb12 and BBMN68 than native κ-casein. The bifidobacterium viability and p H drop were dependent on the added hydrolysates. The addition of κ-casein hydrolysates improved the viability of Bb12 and BBMN68 to a variable extent. The κ-casein hydrolysate produced with papain ( KCHP) is the best for Bb12 and κ-casein hydrolysate produced with trypsin ( KCHT) is the best for BBMN68. Proper amino acid profiles improved the viability of Bb12 and BBMN68. The bifidobacterial growth-promoting capacity of κ-casein hydrolysate may be due to its high content of Ala, Met, Tyr, Phe and Arg residues, especially Tyr which is richer in para-κ-casein than in casein glycomacropeptide ( GMP). In addition, the sialic acid content of κ-casein hydrolysate produced with the tested proteases did not show a direct relationship with its bifidobacterial growth-promoting effect. The obtained peptides possessed growth-promoting activity for Bb12 and BBMN68 existed in para-κ-casein. [ABSTRACT FROM AUTHOR]

Bioactive peptides derived from milk proteins are of great scientific and applied interests due to their diversity and potential health benefits. Peptides of mineral-binding, opioid, angiotensin I-converting enzyme (ACE)-inhibitory, immunomodulatory, cytotoxicity, anticarcinogenic, antibacterial, and antithrombotic activities have been isolated and characterized mainly from cow milk proteins. Variations in the bioactive peptides derived from milk proteins of different mammals can be expected depending on the degree of homology between these proteins. This review focuses on the isolation and characterization of peptides of different bioactivities from milk protein hydolyzates and products of buffalo, camel, goat, mare, sheep, and yak milks. [ABSTRACT FROM PUBLISHER]

Streptomyces transglutaminase (TGase) purified from high-salt medium was characterized and applied into yak yogurts. The purified enzyme presented a Mi-chaelis constant of 40.47 mmol and a maximum velocity of 44.44 U/mg of protein for N-carboxybenzoyl-l-glutaminyl-glycine in the hydroxamate procedure. The purified TGase exhibited optimum activity at 55°C and pH 6.0. The enzyme was not stable above 50°C and was stable within a pH range of 5.0 to 10.0 at 4°C for 12 h and pH 5.0 to 9.0 at 37°C for 30 min. The TGase activity was not affected by Ca2+, K+, Ba2+, or Na+, but slightly inhibited by Fe2+, Mg2+, and Mn2+, and strongly by Cu2+ and Zn2+. To explore yak milk products, it was used to produce yogurt and TGase was used. It was found that TGase-catalyzed cross-linking was effective in improving functional properties of stirred yak yogurt. Treated yogurt produced a strong acid gel, higher consistency, cohesiveness, index of viscosity, and creamier mouth feel than the untreated product. Furthermore, yak yogurt treated with TGase presented lower wet yak hair or sweat odor, or both. Therefore, TGase can be used to pave the way for exploration of novel yak products to overcome the issues of peculiar wet yak hair or sweat odor, or both. [ABSTRACT FROM AUTHOR]

Twelve elements were analyzed by the ICPAES method for macro (calcium, phosphorus, sulphur, magnesium, potassium, sodium) and micro (cobalt, chromium, copper, iron, zinc, manganese) elements. The macro and micro elements of yak (Qilian) milk were analyzed among different farms and a significant difference was found in phosphorus and sulphur concentrations (P<0.05). Potassium) and sulphur concentrations in yak milk were higher while calcium concentrations were similar to cow milk but lower than milk of other species. Sodium, magnesium and phosphorus concentrations found in this study were in the midrange of those in milk of different animal species. The higher concentrations of potassium and lower concentrations of sodium found in yak milk should be of benefit to patients with hyperpiesia. The composition of yak milk was particularly rich in cobalt, manganese and chromium, while it was deficient in zinc. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Yak milk contains a greater percentage of protein and has better quality than bovine milk. There has been an increasing focus on yak milk and milk products during the last few years. In the present study, a PCR-based assay was developed for the specific identification of bovine milk in yak milk by designing 3 primers targeting the mitochondrial ND1 gene. The use of 3 primers in a single PCR reaction set yielded 2 amplification fragments of 293 and 190 bp from bovine milk DNA, whereas only 1 amplification fragment of 293 bp was obtained in yak milk DNA. The technique was applied to raw and heat-treated binary mixtures of yak and bovine milks and enabled the specific detection of bovine milk with a detection limit of 0.1%. The assay developed is sensitive, fast, and straightforward, and it might be useful in the quality control of yak milk and milk products. [ABSTRACT FROM AUTHOR]

Yak milk is a type of milk that people are less familiar with due to its remote geographical location, the particular geographical environment and climatic conditions in Tibet, which may have significant effects on composition, microbiota and fermentation outcome. To investigate the chemical composition and microbiota of fresh and fermented yak milk, and to isolate and characterize the predominant microorganisms in the fermented milk, yak milk (24 fresh and 30 fermented milk samples) was collected from four areas of different altitudes in Tibet, and their microbiological profile and chemical composition were investigated. Yak milk had a higher fat, crude protein, lactose and dry matter content than cow milk. The fermented yak milk showed a great diversity in fat and dry matter levels due to the different ways of processing in different localities, and lower pH and higher lactic acid content compared with commercial cow milk yogurt. Fermented yak milk had a better sanitary quality than fresh yak milk. Three species of lactobacilli (Lactobacillus fermentum, Lactobacillus helveticus and Lactobacillus curvatus) and five species of yeast (Saccharomyces cerevisiae, Candida kefyr, Candida lambica, Candida famata and Candida holmii) were identified phenotypically and encountered as predominant fermentation microbiota. The predominant lactic species in fermented milk was L. fermentum. [ABSTRACT FROM AUTHOR]

The article provides an analysis of the composition of yak's (Maiwa breed) milk in China which includes its chemical composition, mineral, fatty acid, amino acid and protein profiles. Samples of fresh milk are taken from seven mid-lactating yak in Hongyuan county of Sichuan Province. It is stated that the mean values of gross composition of China's yak milk is lower compared to the milk from yak in Nepal and Mongolia.

Simple Summary: Native values of herbage grown at different phenological periods and rumen diversity of microbial population would impact rumen fermentation end-products and milk compositions of yaks (Bos grunniens). The research was conducted in 12 female yaks grazing on the Qinghai-Tibet Plateau (QTP). The results revealed that the phenological periods (VS: Vegetative stage, May; BS: Bloom stage, August; SS: Senescent stage, December) significantly influenced the nutritive values of herbages, microbial diversity and, as a consequence affected on the yak milk yield and compositions. We concluded that the observed differences resulted from the combined effects of phenological periods, herbage composition, and herbage availability. The findings of this study were of great value and useful for current understandings and onwards to conduct further research and for possible practical implementation for the yak cows grazing on QTP. To estimate how native herbage of three different phenological periods modify rumen performance and milk quality of yak grazing alpine meadow. In this study, milk composition and the diversity of the rumen microbial community were measured in 12 full-grazing female yaks on the Qinghai-Tibet Plateau (QTP). The nutrient composition of three phenological periods was determined: Vegetative stage (VS), bloom stage (BS), and senescent stage (SS). High-throughput sequencing of the bacterial 16S rRNA gene was used. The results showed that crude protein (CP) content of herbage in BS was higher than that in vs. and SS (p < 0.05), and neutral detergent fiber (NDF) content of herbage in SS was higher than that in vs. and BS (p < 0.05). Milk solids and fat contents were higher in the vs. and SS than in BS (p < 0.05). However, milk protein content was higher for the vs. and BS than those for SS (p < 0.05). The total volatile fatty acid (VFA), acetate, and propionate concentrations were higher in vs. and BS than in SS (p < 0.05). The community richness estimates (Chao1 estimator) of vs. were higher than that in BS and the SS (p < 0.05). The diversity indices (Shannon index) of the BS were higher than that vs. and the SS (p < 0.05). Spearman correlation analysis between the milk composition, ruminal fermentation parameters, and the relative abundances of the rumen bacteria showed that milk protein content, total VFA, acetate, and propionate concentrations were positively correlated with the relative abundances of the genera Desulfovibrio, Prevotella_1, and Butyrivibrio_2 and was negatively correlated with Olsenella, Ruminococcaceae_UCG.010, and Rikenellaceae_RC9_gut_group abundances. Collectively, the results revealed that there were significant differences in nutrient composition of herbage, chemical composition of yak milk, and microbial diversity in rumen at different phenological stages. The correlations between ruminal fermentation parameters, chemical constituents of yak milk, and some genera of ruminal bacteria might be indicative that the ruminal fermentation parameters and chemical constituents of yak milk are strongly influenced by the rumen bacterial community composition. [ABSTRACT FROM AUTHOR]