| In this dissertation project, a modified atmosphere packaging (MAP) system rich in CO2 was studied for its influence on microbiological and physicochemical stability of raw and precooked red claw crayfish tail meat and the possible mechanism underlying the quality protection.In experiment 1, raw shell-on red claw tails packaged with MAP (80% CO 2/10% O2/10% N2), polyvinylchloride packaging (PVCP) and vacuum packaging (VP) were stored at 2°C for up to 14 days. MAP suppressed (P < 0.05) the growth of aerobic bacteria and coliforms and tended to retard lipid oxidation, inhibited Ca-ATPase activity change, but produced more intense protein denatuation, when compared with VP and PVCP (P < 0.05). However, it promoted proteolysis, cooking loss, and toughening of sample. Sensory panel results were in general agreement with the observed physicochemical changes. In experiment 2, shelf-life of precooked and peeled red claw tails stored in the three packaging systems at 2°C was investigated. MAP almost completely inhibited aerobic bacteria and coliforms. Moreover, it reduced purge loss and texture deterioration when compared with PVCP or VP (P < 0.05). In experiment 3, frozen storage stability (-20°C) of raw red claw tails was evaluated. MAP and VP lowered total plate and coliform counts in 12-month samples when compared with PVCP (P < 0.05). With MAP, more Ca-ATPase activity and sulfhydryls were retained (P < 0.05). However, the MAP treatment aggravated cooking loss and increased toughness of meat (P < 0.05). In experiment 4, proteolytic activity in postmortem muscle was determined using red swamp crayfish as a model. Crude extracts from the crayfish digestive tract did not have an apparent role in muscle proteolysis. However, high m-calpain activity was identified in MAP samples on day 10, coinciding with loss of calpastatin. The observed proteolytic activity and protein degradation did not corroborate with muscle textural properties, suggesting that other physicochemical factors were also involved.Thus, MAP offered an attractive means to preserve microbiological shelf-life of refrigerated and frozen red claw muscle. However, its effect on textural properties of samples depended on whether samples were cooked, and could not be explained by muscle endogenous proteases.Keywords: Red claw crayfish, Modified atmosphere packaging, Microbiology, Proteolysis, Physicochemical quality. |
