Inhibition of endogenous protease activity and protection of histomorphical integrity during refrigerated storage of grass carp fillets by treatment with natural edible di- and tri-carboxylic acids

In this study, by dipping grass carp fillets with 10 mM di- and tri-carboxylic acid solutions individually before storage at 4 degrees C for 10 days, the application potential of these acids in mitigating softening of fish was investigated through analysing shear force, pH, endogenous cathepsin activities, myofibrillar proteolysis and histomorphological characteristics. The results suggested that maleic acid, fumaric acid and tartaric acid were significantly effective against softening of grass carp muscle, as shown by shear force 26%-31% higher than that of control after storage. Acid treatments led to a decline in the pH of muscle. Besides, the inhibitory effect of these acids on cathepsins was demonstrated by activity reduction by 20%-90%. Further, sodium dodecyl sulphate-polyacrylamide gel electrophoresis and heat shock protein (HSP) analysis supported the protection of these acids against degradation and dissociation of myosin and actin through suppressing HSP loss. Moreover, histomorphological images with higher intensity of acridine orange fluorescence in muscle revealed the improvement of tissue integrity by acid treatments. The inhibitory potential of these acids in suppressing softening of fish muscle is particularly relevant to their capacity of mitigating cathepsin-induced proteolysis and improving lysosome stability. Therefore, di- and tri-carboxylic acids could play pleiotropic functions in the quality control of fish fillets.

Automated summary

Dipping grass carp fillets in certain acid solutions can effectively mitigate fish softening, inhibit cathepsin activity, and improve lysosome stability, thus protecting myosin and actin from degradation and dissociation and enhancing muscle tissue integrity.