Key enzymes and reaction pathways driving intensified fishy odor in chilled grass carp fillets: Kinetic analysis of “substrate-enzyme” simulated systems

This study elucidated enzymatic pathways driving fishy odor intensification in chilled grass carp fillets. Lipoxygenase (LOX), hydroperoxide lyase-LOX (HPL-LOX), and phospholipase (PLA) inhibitors reduced fishy odorants by 67.31%, 91.89%, and 58.23%, respectively, while lipase (LPS) inhibition showed no effect. Substrate-enzyme simulation systems [lysophosphatidylcholine (LPC) with PLA, LOX, HPL, LOX-PLA, LOX-HPL, or LOX-PLA-HPL] revealed pathways via kinetic analysis. LOX directly oxidized LPC to LPC-hydroperoxide (LPCOOH), which was cleaved by LOX-HPL to odorants (k = 0.765). In the presence of PLA, hydrolysis of LPC released free fatty acids (FFAs); LOX then catalyzed FFA and LPC oxidation to fatty acid hydroperoxides (ROOH) and LPCOOH, generating odorants via LOX-HPL cleavage (k = 1.056). LOX exhibited higher affinity for FFAs versus LPC, while HPL favored ROOH over LPCOOH. These results identify LOX-PLA-HPL synergy as the core mechanism for fishy odor generation, providing a theoretical foundation for targeted enzyme inhibition in aquatic product preservation.