Protease activity in post-mortem red swamp crayfish (Procambarus clarkii) muscle stored in modified atmosphere packaging

Protease activity during storage is thought to be an important contributor to decreased shelf life of fresh seafood. To examine this, three batches of red swamp crayfish (Procambarus clarkii) tails, placed on trays, were packed with a polyvinyl chloride film (aerobic packaging or AP), under vacuum (vacuum packaging or VP), or under a modified atmosphere (MAP: 80% CO2/10% O-2/10% N-2), and proteolytic activity was measured on days 0, 1, 3, 6, and 10 during storage at 2 degrees C. The crude extract from the crayfish digestive system (gut) did not have an apparent role in muscle proteolysis as negligible proteolytic activity was detected. However, the loss of calpastatin (the endogenous calpain inhibitor) was identified in MAP-stored muscle samples on day 10, suggestive of high m-calpain activity. Tail samples stored in AP showed no appreciable proteolysis, but those stored in MAP and VP showed significant decreases in the levels of 53, 66, 71, and 110 kDa polypeptides during storage. The observed proteolytic activity and myofibrillar protein degradation did not correspond to muscle textural properties as the MAP samples had an increased toughness (P < 0.05) after storage for 10 days. These findings suggest that other physicochemical mechanisms are involved in postmortem alteration in the crayfish muscle structure under the packaging systems investigated.