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Post mortem tenderization is one of the most unfavourable quality changes in fish muscle and this contrasts with muscle of mammalian meats. The tenderization can be partly attributed to the acid lysosomal cathepsins and cytosolic neutral calcium-activated calpains. In this study, these proteases from fish and bovine muscles were quantified and compared. The cathepsin B and L activities were in more important amounts in sea bass white muscle than in bovine muscle. On the other hand, cathepsin D activity was 1.4 times higher in meat that in fish muscle, while cathepsin H was negligible in both muscles. Calpain activities were similar in both types of muscle. Moreover, calpastatin (calpain endogenous inhibitor) level is 3.9 times higher in sea bass white muscle. These differential activities are considered in relation to their probable involvement in post mortem degradation of muscle. (c) 2006 Elsevier Ltd. All rights reserved.

The variations in the amounts of milli-calpain and its specific inhibitor in the white muscle of sea bass (Dicentrarchus labrax) during storage at 4 degreesC for up to 7 days were determined after separation by hydrophobic chromatography on a Phenyl Sepharose vel. There was a significant decline in post-slaughter m-calpain activity with an important inter-individual variability in the rate of decrease of the total activity. In contrast with the calpastatin of mammalian post mortem muscles, calpastatin remained constant within fish muscles after death. The initial levels of protease and inhibitor activities, and their behaviour through post mortem storage. are discussed and implications for the mechanism of tenderisation of fish muscle are suggested. (C) 2003 Elsevier Ltd. All rights reserved.