Stunning stress-induced textural softening in silver carp (Hypophthalmichthys molitrix) fillets and underlying mechanisms.

• Stunning stress resulted in textural softening and poor water retention of fillets. • Stunning stress led to myofibril fragmentation and detachment from sarcolemma. • Stunning stress facilitated cathepsin B and L releases in myofibrils. • Myofibril segmentation and increased cathepsin contributed to fillet softening. This study aimed to investigate the effect of stunning stress on textural properties and water-holding capacity (WHC) of silver carp (Hypophthalmichthys molitrix) fillets and its underlying mechanisms based on intrinsic proteases activity, myofibril microstructure, and myowater dynamic measurements. The results suggested that compared with the non-stressful percussion, ice/water and gill cut stunning resulted in accelerated muscle tenderization with intensive myofibril disintegration and sarcolemma-myofibril detachments. Myowater mobility and distribution were altered by stunning stress, in which gill cut facilitated the migration of immobilized water and free water, thus enhancing the centrifugation loss. In addition, stunning stress promoted the activation of endogenous proteases and the release of cathepsin B and L from lysosomes to myofibrils, which showed significant (P < 0.01) correlations with decreased shear force and elevated myofibril fragmentation index of fillets. Therefore, faster accumulation of cathepsins and myofibril disintegration together contributed to the weakening of texture and WHC in stunning-stressed fish fillets. [ABSTRACT FROM AUTHOR]