Untargeted metabolomic profiling, nutritional composition and enzyme changes on Bigeye tuna ( Thunnus obesus) during cold storage by HPLC-MS coupled with logistic regression

Bigeye tuna is a protein-rich fish that is susceptible to spoilage during cold storage, however, there is limited information on untargeted metabolomic profiling of bigeye tuna concerning spoilage-associated enzymes and metabolites. This study aimed to investigate how cold storage affects enzyme activities, nutrient composition, tissue microstructures and spoilage metabolites of bigeye tuna. The activities of cathepsin B, H, L increased, while Na⁺/K⁺-ATPase and Mg²⁺-ATPase decreased, α-glucosidase (AG) and β-1,4-N-acetylglucosaminidase (NAG), lipase and lipoxygenase first increased and then decreased during cold storage, suggesting that proteins undergo degradation and ATP metabolism occurs at a faster rate during cold storage. Nutrient composition (moisture, protein, and lipid content), free amino acids, total amino acids decreased, suggesting that the nutritional value of bigeye tuna was reduced. Besides, a logistic regression equation has been established as a food analysis tool and assess the dynamics and correlation of the enzyme of bigeye tuna during cold storage. Based on untargeted metabolomic profiling analysis, a total of 484 metabolites were identified as significantly differential metabolites in the bigeye tuna contained several spoilage metabolites involved in lipid metabolism (1-Acyl-sn-glycero-3phosphocholine, Glycerophosphocholine, Choline phosphate), amino acid metabolism (L-Histidine, 5-Deoxy-5'-(methylthio)adenosine, 5-Methylthioadenosine), carbohydrate metabolism (D-Gluconicacid, beta-D-Fructose 1,6-bisphosphate, D-Glyceraldehyde 3-phosphate). The results of tissue microstructures of tuna showed a looser network and visible deterioration of tissue fiber during cold storage. Therefore, metabolomic analysis and tissue microstructures provide insight into the spoilage mechanism investigations on bigeye tuna during cold storage.