Physical and Chemical Changes in Fresh Chilled Muscle Tissue of Common Carp (Cyprinus carpio L.) Packed in a Modified Atmosphere

Abstract

The aim of the study was to monitor the course of physical and chemical changes taking place in stored fresh chilled muscle tissue of carp packed in modified atmosphere (MAP), and to determine its shelf life. Samples of muscle tissue of common carp (Cyprinus carpio, L.) were packed in MAP (80% O2, 20% CO2) and stored for 15 days at +2 ± 2 °C max. During the storage period, O2 level in packs decreased from 78.7 ± 0.39% (day 1) to 63.8 ± 1.30% (day 15). Decrease in O2 in packs between storage days 7 and 9 was highly significant (p < 0.01). During storage, muscle tissue pH decreased during the experiment from 6.46 ± 0.22% (day 1) to 6.17 ± 0.10% (day 15). Levels of N-substances of low-molecular character increased during the experiment from 12.33 ± 2.11 (day 1) to 20.07 ± 3.16 mg 100 g-1 (day 15). Hydrolytic lipid decomposition (FFA) was more intensive in carp muscle tissue (2.09 ± 1.07% total lipid as oleic acid) than in carp skin (1.01 ± 0.31% total lipid as oleic acid) (day 15). Lipid oxidation (PV) in skin showed differences from lipid oxidation in muscle tissue. Oxidation processes in muscle correlated positively with the length of storage (r = 0.90). Over the storage period, peroxide levels increased from 2.58 ± 1.19 mekv O2 kg-1 (day 1) to 6.76 ± 1.78 mekv O2 kg-1 (day 15). Because of low TVBN levels in muscle tissue, shelf life was limited mainly by sensory changes (green discoloration, odour deviations, slime production), which were observed from storage day 9 onwards. It was found that the maximum shelf life of carp packed in MAP (80% O2, 20% CO2) was 7 days. The optimum parameter to determine the remaining shelf life of common carp muscle tissue stored at +2 ± 2 °C max is the TVBN level. As concerns shelf life, TVBN levels in carp muscle should not exceed 15 mg 100 g-1. This level of TVBN (max. 15 mg 100 g-1) for carp (MAP 80% O2, 20% CO2) is much more lower in comparison with levels TVBN (max 25 - 35 mg 100 g-1) which have been determined by Commission Regulation (EC) No. 2074/2005 for sea fish. For that reason we suggest to amplify the study by other monitoring (higher number of samples, various breeds of carp in different weight categories for all the year). On the basis of these analyses the level of TVBN for carp could be determined and incorporated to the legislation.