Metabolomics approach reveals high energy diet improves the quality and enhances the flavor of black Tibetan sheep meat by altering the composition of rumen microbiota

Abstract

This study aims to determine the impact of dietary energy levels on rumen microbial composition and its relationship to the quality of Black Tibetan sheep meat by applying metabolomics and Pearson's correlation analyses. For this purpose, UHPLC-QTOF-MS was used to identify the metabolome, whereas 16S rDNA sequencing was used to detect the rumen microbiota. Eventually, we observed that the high energy diet group (HS) improved the carcass quality of Black Tibetan sheep and fat deposition in the longissimus lumborum (LL) compared to the medium energy diet group (MS). However, HS considerably increased the texture, water holding capacity (WHC), and volatile flavor of the LL when compared to that of MS and the low energy diet group (LS). Metabolomics and correlation analyses revealed that dietary energy levels mainly affected the metabolism of carbohydrates and lipids of the LL, which consequently influenced the content of volatile flavor compounds (VOCs) and fats. Furthermore, HS increased the abundance of Quinella, Ruminococcus 2, (Eubacterium) coprostanoligenes, and Succinivibrionaceae UCG-001, all of which participate in the carbohydrate metabolism in rumen and thus influence the metabolite levels (stachyose, isomaltose, etc.) in the LL. Overall, a high-energy diet is desirable for the production of Black Tibetan sheep mutton because it improves the mouthfeel and flavor of meat by altering the composition of rumen microbiota, which influences the metabolism in the LL.

Keywords: black Tibetan sheep; dietary energy levels; meat quality; metabolomics; rumen microbiota.

Figure 1

The fingerprint of volatile flavor compounds obtained from the longissimus lumborum of Tibetan sheep under different energy level diets. M: monomer, D: dimer, T: polymer. 1–7 means unidentified compounds.

Figure 2

3D PCA score of the overall samples in the positive (A) and negative (B) ion detection mode. The HS group is marked as red, the MS group is marked as green, the LS group is marked as blue, and the QC samples are indicated with purple. PC1 represents principal component 1, PC2 represents principal component 2, and PC3 represents principal component 3.

Figure 3

Venn diagram illustrates the overlap of differential metabolites connected with the KEGG metabolic pathways among the three comparisons (HS vs. MS; HS vs. LS; MS vs. LS) in the longissimus lumborum of Tibetan sheep. The color red and blue represent the upregulation and downregulation of metabolites, respectively.

Figure 4

The enrichment of KEGG metabolic pathways of differential metabolites in the longissimus lumborum of Tibetan sheep. In the bubble diagram, each bubble represents a metabolic pathway. The larger the bubble is, the greater the impact factor is; the darker the bubble is, the more significant the degree of enrichment is.

Figure 5

OTUs Venn diagram of the overlap of rumen microbiota among the three groups (A). Anosim analysis (B) and PCoA plot (C) of the overall samples of rumen microbiota. Relative abundance of bacteria community proportion at the phylum (D) and genus (E) levels among the three groups. Boxplot of the prediction of the most important diff rumen function (F).

Figure 6

(A) The correlation heat map between meat quality parameters and muscle metabolomics analysis. (B) The correlation heat map between muscle metabolomics analysis and rumen bacteria. The color red and blue represent positive and negative correlations, respectively. *P < 0.05 and **P < 0.01. G: glycerol; PE: phosphoethanolamine; GP(2): glycerophosphate(2); GPC: glycerophosphocholine.

Figure 7

Hypothesized scheme pathways and potential mechanisms related to the changes in rumen microbiota, muscle metabolome, and meat quality. Metabolites and bacteria in blue and red indicate them downregulated and upregulated significantly in each comparison, respectively. The gray line denotes the regulatory pathways of meat quality. A: adenine; HAT: hypoxanthine; HxR: inosine; PE: phosphoethanolamine; GP(2): glycerophosphate(2); GPC: glycerophosphocholine; LA: linoleic acid; G: glycerol. pHd: the extent of pH decline (within 24 h after slaughter).