Protein degradation mechanisms during refrigerated storage of gazami crab (Portunus trituberculatus) at endogenous and microbial-derived enzyme levels

During storage, the proteins of gazami crab (Portunus trituberculatus) are prone to hydrolysis into amino acids and biogenic amines, in which enzymes play a critical role. However, studies exploring spoilage mechanisms from the perspective of enzymes are limited. This study identified 84 endogenous and 52 microbial-derived proteolytic enzymes and peptidases by proteomics and metagenomics. There are 7 endogenous amino acid deaminases, primarily degrade glutamate and aspartate. Additionally, 25 amino acid deaminases of microbial origin were identified, which mainly degrade serine. The formation of biogenic amines involved 14 enzymes, all of which were microbial in origin, primarily synthesizing putrescine from arginine. The main microbial contributors to these enzymes were Photobacterium, Vibrio, and Aliivibrio, accounting for 63.87 %, 15.51 %, and 8.69 % at the end of refrigeration, respectively. This study provides insights into the mechanisms of quality deterioration in gazami crab during refrigeration, from the perspectives of metabolic enzymes and microbial activity.