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In order to evaluate the relationship between of endogenous enzymes and physiochemical indicators during the processing of dry-salted Decapterus maruadsi produced by the traditional method. The evolution of the endogenous enzymes (cathepsin B, cathepsin L, cathepsin H, acid lipase, neutral lipase, and phospholipase) and physical and chemical parameters (moisture content, salt content and pH) of dry-salted Decapterus maruadsi during processing were investigated. Principal component analysis and Pearson correlation coefficient analysis were used to explore the main factors influencing the endogenous enzyme activity and the interactions between endogenous enzymes. The following results were observed during the processing of dry-salted Decapterus maruadsi: the salt content could stimulate cathepsin (L and B) activity and inhibit lipase activity; a lower moisture content could inhibit lipase activity, while the inhibitory effect on cathepsin was inconspicuous; pH had a minor influence on the endogenous enzyme activities; cathepsin B and L could partially inhibit lipase activity.

Extensive proteolysis and formation of flavor substances occur during the processing of dry-salted fish due to the action of endogenous proteases. This study analyzed the evolution of the endogenous proteases and the relationship between endogenous protease levels and protein degradation during processing. Cathepsin B and L activity increased significantly during the last two stages, while cathepsin H activity decreased non-significantly (residual activity was 92.27%) compared to initial activity levels in fresh fish. Dipeptidyl peptidase (DPP I, IV) activity decreased overall. The activity of three aminopeptidases (arginine aminopeptidase; alanyl aminopeptidase; leucyl aminopeptidase) initially decreased (P