Optimizing the use of the alcoholic extract of Nannochloropsis sp. on the shelf life of Metapenaeus affinis fillets

After catching, aquatic animals undergo chemical, microbial and sensory changes, which cause them to spoil and reduce the shelf life of the product. The purpose of this study was to use edible chitosan coating containing the alcoholic extract of Nannochloropsis sp. on the shelf life of Metapenaeus affinis. For optimization, different concentrations of algae extract (0, 1.5 and 3%), temperature (-10, -3 and 4°C) and storage time (0, 7 and 15 days) were considered as independent variables. Based on the output of RSM software, 15 treatments were selected, and variance analysis was used to determine the suitability of the obtained models. Peroxide value (PV), thiobarbituric acid (TBA), total volatile nitrogen bases (TVB-N), free fatty acids (FFA), total aerobic bacteria (TVC) and color changes (L*, a*and b*) were investigated. Based on the results, the amount of microbial, chemical and indicators of shrimp fillet decreased significantly with the increase in the concentration of algae extract compared to the control group (P<0.05). On the seventh and fifteenth days of storage, the ninth and twelfth treatments showed the lowest bacterial load with 3.22±0.64 Log CFU/g and 4.60±0.65 Log CFU/g (P<0.05). The increase in extract concentration and temperature caused the increase of a* and b* indices and the decrease of L* color index. The percentage of fat and weight yield of shrimp fillet increased significantly with the increase in extract concentration (P<0.05). Based on the results of quality indicators, shrimp fillet at -10°C and 3% extract concentration was favorable for human consumption. According to F-value, in all indicators, temperature was more influential compared to time. The proposed formulas for each index were able to predict the quality changes of shrimp fillet.