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Role of Lysosomes and Cathepsins in Atlantic salmon flesh degradation

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Kjetil Aune

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IBIO 2010; Dalian, China, 2010-07-24–2010-07-27

Bahuaud, Diane; Mørkøre, Turid; Mørkøre, Turid; Østbye, Tone-Kari; Østbye, Tone-Kari K; Thomassen, Magny S.; Ruyter, Bente; Veiseth-Kent, Eva; Ofstad, Ragni

After years of consideration as garbage organelles, lysosomes and their acid hydrolases are today recognized as the major intracellular proteolytic system in numerous animal species including humans. Cathepsins B, D and L are lysosomal enzymes playing the most important role in fish muscle softening. Lysosomes and cathepsins are also involved in starvation, spawning migration and acclimation to variations of temperature, related to protein breakdown to encounter these special conditions. For fish consumers, fillet texture is one of the most important quality parameters. In contrast to mammalian meat, a firm and elastic flesh is often preferred in fish. We aimed at studying the implication of lysosomes and cathepsins B and L, in muscle structure degradation and texture of Atlantic salmon. Super-chilling, dietary lipids, pre-slaughter stress and genetic background had an impact on the lysosomal network and the activation of lysosomal enzymes influenced the final salmon flesh quality. Super-chilling formed ice-crystals in the fillet, accelerating the release of cathepsins into the cytosol, and so, fillet degradation. The presence of >60% of dietary PUFAs disturbed the lysosomal network, having negative effects on salmon fillet structure. A drop in muscle pH after pre-slaughter stress increased cathepsin activities, which also resulted in salmon fillet degradation. Finally, in different salmon genetic families, the higher the cathepsin L activity was in the muscle, the softer the fillet; strongly suggesting that enzymatic activity may have a direct impact on fillet firmness. Total cathepsin B and/or cathepsin L activities and/or gene expressions in Atlantic salmon muscle were negatively correlated to muscle pH, myofibre-myofibre and myofibre-myocommata attachments, and fillet firmness. Cathepsins B and L were influenced by biochemical factors and seem to play an important role in salmon flesh degradation pre- and post-mortem. They should highly be considered in salmon quality production and consumption for consumer and farmer satisfaction.

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