In this study, non-targeted metabolomics based on ultra-high performance liquid chromatography Q-Exactive-mass spectrometry (UPLC-Q-Exactive-MS) was used to explore the differences in the metabolite profiles of muscles from Bactrian camels slaughtered at different ages. The results showed that a total of 710 differentially expressed metabolites (DEMs) were identified in the longissimus dorsi muscle of camels from three age groups: Ⅰ (3–4 years old), Ⅱ (6–7 years old), and Ⅲ (9–10 years old). In total, 78 DEMs were found in groups Ⅰ vs Ⅱ, of which 47 were upregulated in group Ⅰ and 31 were upregulated in group Ⅱ. Totally, 49 DEMs were identified in groups Ⅱ vs Ⅲ, of which 18 were upregulated in group Ⅱ and 31 were upregulated in group Ⅲ. In addition, 65 DEMs were identified in groups Ⅰ vs Ⅲ, of which 29 were upregulated in group Ⅰ and 36 were upregulated in group Ⅲ. The results of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that the DEMs were mainly enriched in pathways such as protein and amino acid metabolism, fatty acid metabolism, and vitamin and mineral metabolism, indicating that the digestion and metabolism of various nutrients in camels were different at different growth stages. The contents of polyunsaturated fatty acids (PUFA) (especially n-6 PUFA and n-3 PUFA) and the PUFA/unsaturated fatty acid (UFA) ratio were significantly higher in group Ithan Ⅲ, which was mainly related to the significant upregulation of arachidonic acid, linoleic acid and 13-L-hydroperooleic acid concentrations in relevant metabolic pathways. Meanwhile, DEMs such as L-leucine, L-valine, and L-glutamine could serve as potential markers for evaluating the quality change of camel meat at different slaughter ages.

The differences in the proteomes of camel meat from different age groups were analyzed by tandem mass tag (TMT)-based quantitative proteomics and liquid chromatography tandem mass spectrometry (LC-MS/MS) to identify the key quality-related proteins of camel meat. The results showed that differentially expressed proteins (DEPs) had an important effect on the quality of camel meat. A total of 311 DEPs were identified in the longissimus dorsi muscle of camels from three age groups, 3-4 (Ⅰ), 6-7 (Ⅱ), and 9-10 (Ⅲ) years old. Altogether 245 DEPs were identified in groups Ⅰ versus Ⅱ, 16 in groups Ⅱ versus Ⅲ, and 139 in groups Ⅰ versus Ⅲ. In addition, 194, 1, and 110 DEPs were up-regulated, and 51, 15, and 29 DEPs were down-regulated in the three comparison groups, respectively. Gene Ontology (GO) functional annotation analysis indicated that structural proteins, metabolic proteins, and heat stress proteins could be used as biomarkers for discrimination among camel meat from different ages. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that the DEPs were mainly involved in fatty acid metabolism, glycolysis/glucose production, amino acid biosynthesis, and the hypoxia inducible factor-1 (HIF-1) signaling pathway. Protein-protein interaction (PPI) analysis showed that metabolic enzyme proteins were key network-connecting proteins that affect camel meat from different ages. Correlation analysis showed that 16 DEPs were correlated closely with meat tenderness. The tenderness of camel meat from the three age groups was mainly influenced by actin, histone and protein kinases. The results of this study can provide a scientific basis for the grading and evaluation of camel meat, the selection of optimal slaughter age, and the study of camel meat quality characteristics.