Analysis of Metabolites in Giant Salamander Meat during Cold Storage Using Non-Targeted Metabolomics Based on Ultra-high Performance Liquid Chromatography-Mass Spectrometry

In this study, non-targeted metabolomics based on ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS) was used to explore the change in the metabolite profile in giant salamander meat during cold storage at 4 ℃ (0, 2, 4 and 8 days). The differences within each group and between the 0- and 2-day storage groups were small, while the intra- and inter-group differences between days 4 and 8 of storage were large. As the storage time increased, the number of differential metabolites between adjacent groups increased gradually. Using the variable importance in the projection (VIP) value of the first principal component in the partial least squares discriminant analysis (PLS-DA) model greater than or equal to two, and the P-value of t-test less than or equal to 0.001 as criteria, a total of 125 differential metabolites were selected, including organic acids and their derivatives (17), esters and their derivatives (53), amino acids and their derivatives (25), nucleotides and their derivatives (13), alcohols (3) and other compounds (14). The abundance of most of the metabolites decreased significantly on 8 day of storage (P < 0.05). The cumulative change in the abundance of the organic acids and their derivatives (A1) had a similar trend to that of the amino acids and their derivatives (A3), that is, there was a small increase from days 0 to 2, a small decrease from days 2 to 4, and a rapid decrease from days 4 to 8. The cumulative changes in the abundance of the esters and their derivatives (A2) as well as the nucleotides and their derivatives (A4) showed a downward trend, but the abundance of the esters and their derivatives (A2) decreased slowly from days 0 to 4 and rapidly from days 4 to 8, while the abundance of the nucleotides and their derivatives (A4) showed a linear downward trend. The results of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis and Pearson correlation analysis showed that histidine metabolism, arginine and proline metabolism, arginine biosynthesis, lysine degradation, taurine and sub taurine metabolism, valine, leucine and isoleucine biosynthesis, and aminoacyl-tRNA biosynthesis and other metabolic pathways had a good correlation with the changes of giant salamander meat quality; at the same time, creatine, L-histidinol, L-glutamate, histidine, ornithine, L-arginine and phytosphingosine could be used as potential markers for evaluating the quality change of giant salamander meat during cold storage. The results of this study provide a theoretical basis for understanding postmortem metabolism in giant salamander muscle and for quality control of giant salamander meat during cold storage.