Effect of chitosan obtained from some aquatic crustacean in the Western Black Sea on the texture profile of rainbow trout (Oncorhynchus mykiss) fillets stored at the refrigerator (+4°c) conditions

From the past to the present, nutrition has been a fundamental need to meet the energy requirements of living beings. Today, meeting this essential requirement has brought along the concept of healthy nutrition. The criterion for a healthy diet can be defined as the intake of organic and inorganic essential ingredients at the rate of the body's daily needs. Fish meat is an important alternative in healthy diet with its high protein, unsaturated fatty acids, and rich mineral content. Aquatic product consumption, while preferred in regions close to the source in the past, has a more widespread consumption area today. This situation has brought problems that emerge during the storing and transporting of aquatic foods. Fish have a high rate of deterioration due to their high moisture content and protein value. Different preservation techniques have been used for many years to delay the spoilage of fish meat. Today, with the developing technology, both these techniques have been developed, and combined methods where these techniques are used together are applied. In this study, trout fillets were coated with chitosan biopolymers, which will increase the protective properties of these techniques and extend the preservation duration. Chitosan is the second most abundant biodegradable substance in nature after cellulose. In addition to being anticarcinogenic, antimicrobial, antifungal, edible, and non-toxic, it has high film-forming properties. It is known that the storage period of fish coated with chitosan is prolonged, and sensory analyzes performed on fish meat yield favorable results. In the present study, wastes of three different crab species, which were discarded as non-target species as a result of fishing activities from the Western Black Sea region, were used. According to the physicochemical analysis results of chemically extracted chitosan in the study, the yield was 9.26%, the moisture was 1.57%, crude ash was 0.91%, and the deacetylation degree was 86.26%. Moreover, among the color parameters, L*, a*, b*, chroma, hue, and whiteness values were found to be 75.50, 7.76, 13.4, 13.33, 1.36, and 72.44, respectively. The visual color evaluation was performed as creamy white. Furthermore, according to elemental analysis results, C, H, and N were determined as 40.935%, 7.053%, and 7.617%, respectively. The rainbow trout fillets were coated with different concentrations of chitosan and stored for 18 days under refrigerator conditions. The color analysis results of rainbow trout fillets showed that the fresh sample's L*, a*, b*, chroma, hue, and whiteness values were 56.47, 1.05, 14.64, 14.70, 1.50, and 54.04, respectively. On the last day of the storage, the L*, a*, b*, chroma, hue, whiteness values were 48.52, 1.04, 13.04, 13.08, 1.49, 46.85 in the control group, 59.12, 1.26, 14.39, 14.45, 1.48, 56.64 in the 0.5% chitosan added group, and 58.30, 1.95, 16.78, 16.89, 1.45, 55.00 in the 1% chitosan added group, respectively. Tissue analysis results of rainbow trout fillets stored under refrigerator conditions (+4°C) showed that the hardness, springiness, cohesiveness, and gumminess values in the fresh sample were 37.674 N, 0.957 g.sec, 0.78 g.sec, and 29.661 g.sec, respectively. On the last day of the storage, the same values were determined to be 85.838 N, 0.894 g.sec, 0.468 g.sec, 40.179 g.sec in the control group, 91.905 N, 0.885 g.sec, 0.471 g.sec, 43.308 g.sec in the 0.5% chitosan added group, and 115.297 N, 0.952 g.sec, 0.565 g.sec, 65.188 g.sec in the 1% chitosan added group, respectively. In conclusion, it was observed that the shelf life of rainbow trout fillets coated with chitosan biopolymers was prolonged compared to the control group during storage in refrigerator conditions.