Protease activity impacts flesh colour during post-mortem storage of farmed Atlantic halibut (Hippoglossus hippoglossus): A condition referred to as chalky halibut

Effects of Ozone Gas and Slightly Acidic Electrolyzed Water on the Quality of Salmon (Salmo salar) Fillets from the Perspective of Muscle Protein

To elucidate the mechanisms of ozone gas (OG) and slight acid electrolyzed water (SA) on the quality changes in texture, water-holding capacity, and softening of salmon, the bacterial growth, total volatile basic nitrogen, thiobarbituric acid reactive substance, a* value, texture properties, carbonyl content and free sulfhydryl content, myofibrillar fragmentation index, and proteolytic activities of salmon treated by OG (1 mg/m3 for 10 min) and SA (ACC 30 mg/L, 5 min) individually and in combination were studied. The results showed that total viable counts of SA + OG (dipped in SAEW for 5 min, followed by exposure to ozone for 10 min) was about 3.36 log CFU/g lower than the control (CK) (dipped in distilled water for 5 min) on day 10. Further studies indicate that at the end of storage, the hardness of SA + OG fillets only decreased by 33.95%, while the drip loss and myofibrillar fragmentation index (MFI) were the lowest (i.e., 14.76% and 101.07). The activity of cathepsin D was extensively inhibited by SA + OG, which was only 2.063 U/g meat at the end. In addition, the carbonyl content was 1.90 μmol/g protein, and the free sulfhydryl content was 39.70 mg/mL in the SA + OG group, indicating that protein oxidation was also effectively inhibited. Correlation analysis shows that bacteria and endogenous proteases are the main causes of protein degradation. Overall, the combination of OG and SAEW is an effective way to maintain the muscle quality of salmon by inhibiting bacterial growth and endogenous enzymes.

Relevance of calpain and calpastatin activity for texture in super-chilled and ice-stored Atlantic salmon (Salmo salar L.) fillets

The aim of the present experiment was to measure the protease activities in ice-stored and super-chilled Atlantic salmon (Salmo salar) fillets, and the effect on texture. Pre-rigour fillets of Atlantic salmon were either super-chilled to a core temperature of -1.5°C or directly chilled on ice prior to 144h of ice storage. A significantly higher calpain activity was detected in the super-chilled fillets at 6h post-treatment compared to the ice-stored fillets and followed by a significant decrease below its initial level, while the calpastatin activity was significantly lower for the super-chilled fillets at all time points. The cathepsin B+L and B activities increased significantly with time post-treatment; however, no significant differences were observed at any time points between the two treatments. For the ice stored fillets, the cathepsin L activity decreased significantly from 6 to 24h post-treatment and thereafter increased significantly to 144h post-treatment. There was also a significantly lower cathepsin L activity in the super-chilled fillets at 0h post-treatment. No significant difference in breaking force was detected; however, a significant difference in maximum compression (Fmax) was detected at 24h post-treatment with lower Fmax in the super-chilled fillets. This experiment showed that super-chilling had a significant effect on the protease activities and the ATP degradation in salmon fillets. The observed difference in Fmax may be a result of these observed differences, and may indicate a softening of the super-chilled salmon muscle at 24h post-treatment.