Computational identification of cathepsin B and L inhibitors and their role in modulating protein degradation and gelation of unwashed grass carp (Ctenopharyngodon idella) mince.

Unwashed fish mince is a sustainable alternative to conventional surimi, however, residual endogenous proteases can degrade myofibrillar proteins and compromise gel quality. In this study, unwashed grass carp (Ctenopharyngodon idella) mince was used as a model system to investigate inhibitory effects and underlying mechanisms of natural compounds on gel deterioration and quality improvement. Based on structural characteristics of cathepsins, molecular docking identified naringin, apigenin, proanthocyanidins and luteolin as potential inhibitors, with proanthocyanidins exhibiting the strongest interactions with cathepsins. All compounds reduced cathepsin activity and myosin degradation, and proanthocyanidins showed the greatest inhibition. These compounds, particularly proanthocyanidins, enhanced storage modulus, gel strength, water-holding capacity and immobilized water proportion of the gels, and the microstructure became denser and more uniform with fewer pores. Overall, these findings propose a protection-reconstruction mechanism by natural compounds in unwashed fish mince gels, in which limited proteolysis and strengthened protein interactions synergistically improve gel quality.