Spoilage Marker Metabolites and Pathway Analysis in Chilled Tan Sheep Meat Based on GC-MS

Metabolic changes of Tan sheep meat maintained at 0 °C for up to 8 d were identified based on gas chromatography time-of-flight mass spectrometry. Total viable counts (TVC), total volatile basic nitrogen (TVB-N) and pH were utilized as freshness indicators during meat storage. A relationship between meat freshness, metabolite accumulation and key metabolic pathways was postulated. Twenty-seven statistically significant metabolites were characterized. D-glyceric acid, phenylalanine, methionine, glucose-1-phosphate, D-(glycerol-phosphate), lysine, ribitol, asparagine and isomaltose were significantly (p < 0.01) correlated to the freshness indicators. A correlation coefficient with gluconic acid, citric acid and trans-4-hydroxy-L-proline and the freshness indicators ranged from 0.539 to 0.911. 1, 5-anhydroglucitol was significantly correlated with pH (p < 0.05) and TVC (p < 0.01). These metabolites were identified as potential spoilage biomarkers. Three major metabolic processes occurred during storage: metabolism of alanine, aspartate, and glutamate; an operational TCA cycle and metabolism of amino sugar and nucleotide sugar.