"The Yak"-A remarkable animal living in a harsh environment: An overview of its feeding, growth, production performance, and contribution to food security

Effect of tremella polysaccharides on the quality of collagen jelly: insight into the improvement of the gel properties and the antioxidant activity of yak skin gelatin

BACKGROUND

The present study aimed to investigate the effects of tremella polysaccharides on the gel properties and antioxidant activity of yak skin gelatin with a view to improving the quality of collagen jellies. The preparation of composite gels were performed by yak skin gelatin (66.7 mg mL-1) and tremella polysaccharides with different concentrations (0, 2, 4, 6, 8 mg mL-1), and finally the collagen jelly was prepared by composite gel (yak skin gelatin: 66.7 mg mL-1; tremella polysaccharides:6 mg mL-1) with the best performance.

RESULTS

Tremella polysaccharides not only improved the hardness, springiness, gel strength, water holding capacity and melting temperature of yak skin gelatin, but also enhanced the composite gel's scavenging activity against ABTS radicals, DPPH radicals, O2 and OH radicals. The filling of tremella polysaccharides into the gelatin network increased the number of crosslinking sites inside the gel, which resulted in the gel network structure becoming dense and orderly. The gel particles became finer and more uniform, and the thermal stability was improved. Furthermore, the sensory score of commercially available gelatin jelly decreased more rapidly during storage compared to the composite gel jelly.

CONCLUSION

The gel properties and antioxidant activity of yak skin gelatin were improved by adding tremella polysaccharides, and then the quality and storage properties of the jelly were improved, which also provided technical reference for the development of functional gel food. © 2024 Society of Chemical Industry.

Genome-Wide Transcriptome Profiling Reveals the Mechanisms Underlying Hepatic Metabolism under Different Raising Systems in Yak

Yak meat is nutritionally superior to beef cattle but has a low fat content and is slow-growing. The liver plays a crucial role in lipid metabolism, and in order to determine whether different feeding modes affect lipid metabolism in yaks and how it is regulated, we employed RNA sequencing (RNA-seq) technology to analyze the genome-wide differential gene expression in the liver of yaks maintained under different raising systems. A total of 1663 differentially expressed genes (DEGs) were identified (|log2FC| ≥ 0 and p-value ≤ 0.05), including 698 down-regulated and 965 up-regulated genes. According to gene ontology (GO) and KEGG enrichment analyses, these DEGs were significantly enriched in 13 GO terms and 26 pathways (p < 0.05). Some DEGs were enriched in fatty acid degradation, PPAR, PI3K-Akt, and ECM receptor pathways, which are associated with lipid metabolism. A total of 16 genes are well known to be related to lipid metabolism (e.g., APOA1, FABP1, EHHADH, FADS2, SLC27A5, ACADM, CPT1B, ACOX2, HMGCS2, PLIN5, ACAA1, IGF1, FGFR4, ALDH9A1, ECHS1, LAMA2). A total of 11 of the above genes were significantly enriched in the PPAR signaling pathway. The reliability of the transcriptomic data was verified using qRT-PCR. Our findings provide new insights into the mechanisms regulating yak meat quality. It shows that fattening improves the expression of genes that regulate lipid deposition in yaks and enhances meat quality. This finding will contribute to a better understanding of the various factors that determine yak meat quality and help develop strategies to improve yield and quality.

Changes provoked by altitudes and cooking methods in physicochemical properties, volatile profile, and sensory characteristics of yak meat

The present study aimed to shed light on the effects of altitudes and three cooking methods (boiling, steaming, and roasting) on the physicochemical quality, volatile profile, and sensorial characteristics of yak meat. Composite meat samples were prepared to represent each cooking method and altitude level from the longissimus thoracis et lumborum (LTL) muscle of nine yaks. The techniques employed were gas chromatography-mass spectrometry (GC-MS) and electronic nose (E-nose) along with chemometrics analysis to study the changes occurring in yak volatile profile, and TBARS measurement in lipid oxidation during cooking. Among the cooking methods, boiling and steaming exhibited higher protein and fat content while lower volatile compound contents. Additionally, roasted yak meat received the highest sensory scores, along with decreased L*-values, while elevated a*- and b*-values, and tenderness. A total of 138 volatile compounds were detected, and among them, 36 odorants were identified as odor-active compounds in cooked yak meat. It is evidenced that low-altitude yak presented more complex and richer flavor profiles than high-altitude ones. Moreover, yak meat from low- and high-altitude was classified into two groups by an electronic nose (E-nose) owing to distinct flavor characteristics. Overall, roasted yak meat originating from low altitudes tends to be more popular from a sensory perspective.

Establishment of SV40 Large T-Antigen-Immortalized Yak Rumen Fibroblast Cell Line and the Fibroblast Responses to Lipopolysaccharide

The yak lives in harsh alpine environments and the rumen plays a crucial role in the digestive system. Rumen-associated cells have unique adaptations and functions. The yak rumen fibroblast cell line (SV40T-YFB) was immortalized by introducing simian virus 40 large T antigen (SV40T) by lentivirus-mediated transfection. Further, we have reported the effects of lipopolysaccharide (LPS) of different concentrations on cell proliferation, extracellular matrix (ECM), and proinflammatory mediators in SV40T-YFB. The results showed that the immortalized yak rumen fibroblast cell lines were identified as fibroblasts that presented oval nuclei, a fusiform shape, and positive vimentin and SV40T staining after stable passage. Chromosome karyotype analysis showed diploid characteristics of yak (n = 60). LPS at different concentrations inhibited cell viability in a dose-dependent manner. SV40T-YFB treated with LPS increased mRNA expression levels of matrix metalloproteinases (MMP-2 and MMP-9), inflammatory cytokines (TNF-α, IL-1β, IL-6), and urokinase-type plasminogen activator system components (uPA, uPAR). LPS inhibits the expression of tissue inhibitors of metalloproteinases (TIMP-1 and TIMP-2), plasminogen activator inhibitor-2 (PAI-2), fibronectin (FN), anti-inflammatory factor IL-10, and collagen I (COL I) in SV40T-YFB. Overall, these results suggest that LPS inhibits cell proliferation and induces ECM degradation and inflammatory response in SV40T-YFB.

High energy level diet improves the growth performance and rumen fermentation of yaks in cold weather

To date, no research has been done on energy requirements for yaks in Tibetan cold weather. The findings of the current study provide proper energy requirements for yaks would facilitate scientific feeding of fattening yaks in cold weather. The metabolomics and 16s rRNA sequencing technologies were used to explore the underlying mechanism that affects the growth performance of yaks fed with different energy levels of diet in cold weather. Three groups of yaks (141.7 ± 3.34 kg) were fed with diets containing metabolizable energy 7.20, 7.89, and 8.58 MJ/kg DM (dry matter) and named the low-, medium-, and high-energy groups, respectively. The results showed that the average daily feed intake of the high-energy group was higher than that of the low-energy group (p  = 0.006). Plasma aspartate aminotransferase (p  = 0.004), alanine aminotransferase (p  < 0.001), and interferon-γ (p  < 0.001) in the high-energy group were lower than in the low-energy group. In contrast, superoxide dismutase (p  < 0.001), immunoglobulin G (p  < 0.001), and interleukin 2 (p  = 0.002) were higher than the low-energy group. The rumen microbial protein (p  = 0.025), total volatile fatty acids (p  = 0.029), and neutral detergent fiber digestibility (p  = 0.050) in the high-energy group were higher than in the low-energy group, whereas the acetate: propionate ratio (p  = 0.001) and ammonium nitrogen (p  = 0.001) were lower than in the low-energy group. The plasma metabolomics results displayed that yaks fed with a high-energy diet augmented the metabolism of arginine, proline, purine, taste transduction, pyrimidine, and glutathione pathways. The relative abundance of Methanobrevibacter in the high-energy group was lower (p  < 0.001), whereas the relative abundance of Methanosphaera (p  < 0.001) was higher than in the low-energy group. The results of the current study suggest that a high-energy diet in growing yaks during the cold season can improve growth performance, rumen microbial protein synthesis, antioxidants, and immunity.

Quantitative N-Glycoproteomic Analysis of Cattle-Yak and Yak Longissimus Thoracis

In this study, the N-glycosylated protein profiles of cattle-yak longissimus thoracis (CYLT) and yak longissimus thoracis (YLT) were comparatively analyzed using quantitative proteomics techniques. A total of 76 differential N-glycosylated proteins (DGPs) were screened from 181 quantified N-glycoproteins, indicating that differences in N-glycosylation levels are key to the differences between CYLT and YLT. In particular, a variety of N-glycoproteins involved in the extracellular matrix were differentially N-glycosylated between CYLT and YLT, mainly including fibrillin-1, fibromodulin, collagen, and laminins. In addition, the N-glycosylation levels of several lysosomal-related proteolytic enzymes (cathepsin D, dipeptidyl peptidase 1, legumain, and aminopeptidases, etc.) were significantly higher in CYLT. These results indicated that the N-glycosylation of CYLT and YLT proteins plays a crucial role in the regulation of extracellular matrix organization (muscle fiber structure) and lysosomal activity (postmortem meat tenderness). The results remind us that posttranslation modifications, especially N-glycosylation, are still icebergs beneath the surface.