Freshness assessment and grading of refrigerated grass carp (Ctenopharyngodon idella) fillets

The current freshwater fish grading methods are simple and unrepeatable. This paper was aimed to provide a grading method for refrigerated grass carp fillets. The color, odor, morphology, texture of raw grass carp fillets and the odor, taste and broth turbidity of boiled grass carp fillets were used for sensory description analysis. According to principal component analysis (PCA) and hierarchical cluster analysis (HCA), the freshness grading of refrigerated grass carp fillets was provided. Physical and chemical indicators including the K value and biochemical indicators such as desmin and troponin T were compared with specified sensory properties. The evaluation of the grading method was given. According to the results of PCA and HCA based on sensory description, refrigerated grass carp fillets can be divided into three freshness levels: 0-1 d (first-level freshness), 2-7 d (second-level freshness), and 8-10 d (three-level freshness). The relative gray values of desmin and troponin T decreased to 95.68 % and 96.75 % at the end of first-level freshness; to 56.4 % and 69.6 % at the end of second-level freshness; to 56.36 % and 52.85 % at the end of third-level freshness respectively. HCA reflected by physical and chemical indicators was consistent with that by specified sensory indicators, indicating that specified sensory properties could reflect the change of freshness of freshwater fish. Troponin T had a similar trend in the change and a potential as freshness indicator. This study provided freshness grading ranges based on specified sensory indicators, and macle an evaluation. On this basis, the relationship between the change of desmin and troponin T, and HCA reflected by specified sensory indicators was investigated. Troponin T could reflect the freshness of refrigerated grass carp fillets effectively. This provides a foundation for developing testing paper for fish in future.