Prediction of shelf life and correlation of quality properties peeled white shrimp (Metapenaeus affinis) during chilling

Introduction: Shrimp is one of the popular seafood consumed in the Iran. In Abadan (West Iran), Metapenaeus affinis, called as king prawn, are caught from marine water (Persian Gulf), processed and sold in the local market or exported. There is a reduction quality due to microbiological and enzymes activities during postmortem storage, which result in undesired odors and off-flavors over time, causing ultimate rejection by the consumer and making shrimp unfit for consumption. Specific spoilage organisms, a few members of the microbial community of freshly caught or processed seafood, produce various volatile compounds such as trimethylamine (TMA) and total volatile nitrogen bases (TVB-N), which could function as indicators of spoilage. Physicochemical indexes (pH, trimethylamine (TMA), total volatile nitrogen bases (TVB-N) and thiobarbitoric acid reactive substances (TBARS) are used to evaluate the freshness of fishery products. White shrimp (Metapenaeus affinis) is a warm-water speciesnative to the eastern Pacific coast from the Gulf of California, Mexico tonorthern Peru. The world aquaculture production of white shrimp was about 4.2 million tonnes with a global market value of USD24.4 billion in 2016. Currently, Pacific white shrimp is themost important species economically, and it is accounted for about 70%of the total shrimp production in the world due to its high nutrient content of amino acids, peptides, polyunsaturated fatty acids, and other useful substances. However, because shrimp is subject to natural contamination by many bacterial species and contain a large amount of non-protein nitrogenous compounds and autolytic enzymes, it is highly perishable and its post-mortem changes occur rapidly, which result in an obvious off-taste and soft texture. In general, sea-food microbiota originates from the skin or intestines of the processed objects, and contamination occurs during the successive steps of food processing. Shrimp spoilage is attributed mainly to the uncontrolled growth and subsequent various metabolic activities of microbiota. It is commonly assumed that only specific spoilage organisms (SSO) participate in the spoilage process, and they produce metabolites that result in off-odors and off-flavors. The identification of SSO that are responsible for spoilage re-quires sensory, microbiological and chemical studies. The growth of SSO results in the breakdown of macromolecules in shrimp, which causes the tissue of shrimp to lose its elasticity and produce off-odors. The modification of microbiota would lead to the change in pattern andprocess of spoilage in shrimp. Therefore, the aim of the present assay is to investigate of different temperatures (ice and refrigerator) on peeled shrimp Metapenaeus affinis.
Material and methods: Freshly caught shrimp Metapenaeus affinis were collected from the Persian Gulf in Khozestan (south Iran). The average weight of shrimp was 15.26±0.05 g per shrimp. Immediately after collection, samples were cooled with ice and transported to the Department of Marine Natural Resources, Khorramshahr University of Marine Science and Technology within 1h. The ratio of shrimp to ice was 1:3 (w/w). Upon arrival, shrimp were peeled and washed in cold water. After draining, shrimp weighing approximately 200 g were packed in a zip bag and were stored at ice and refrigerator. Shrimp samples were kept in ice in a plastic container with drain holes. Shrimp were re-iced daily to maintain the same ratio. All samples were taken for microbiological, physicochemical, and sensory analyses every 4 days for up to 16 days. Average were compared through an Analysis of Variance (ANOVA) and effects were considered significant (by Duncan´s test) when p-value £0.05. Pearson correlation analysis with 95% of confidence interval was used to determine the relationship between time of iced storage and quality parameters.
Results and discussion: Variations in physicochemical index were observed throughout the storage period. Sensory analysis attributes exhibited significant variations and correlations close 0.800 with time storage, which is a showing of the shrimps´ loss of freshness. A regression analysis using the acceptability limit mesophilic counts (7 log cfu/g) yielded a shelf life for white shrimp stored on ice and refrigerator of 7 and 4 days respectively.
Conclusion: The TVBN, microbiological and sensory analysis displayed very strong correlations with storage time, and they may be considered suitable indicators for evaluating white shrimp spoilage stored on ice and refrigerator.