Investigating the Effect of Chitosan Coating Along with Ginger Essential oil on Shelf life of Salmon Fish in Refrigerator Temperature

IntroductionRecently, the use of new packaging materials and natural additives for improving the durability and preservation of foods has been increasingly considered. Edible coatings containing plant extracts lead to increase the shelf life of food, do not cause environmental contamination, and do not endanger the health of the consumer. Fish is a food rich in amino acids, vitamins and minerals, and polyunsaturated fatty acids, especially omega-3, which has made it more and more popular in the human diet. However, the presence of a significant amount of polyunsaturated fatty acids as well as easily digestible proteins has turned fish into a highly perishable commodity. Fresh seafood spoils rapidly due to the enzymatic and bacterial activities that occur after death, as well as the spoilage caused by the oxidation of polyunsaturated fatty acids and the high concentration of hematin compounds and metal ions of fish muscle, such as iron, and their pH which is close to neutral. Therefore, the use of natural coatings that can increase the shelf life of food and attract the consumers should be given more attention. Iran is the largest fishery producer in the region, thus, providing new methods to increase the shelf life of these products until the time of consumption can guarantee the safety and be effective in the economic prosperity of this industry. Therefore, the present study was designed to investigate the effect of chitosan coating along with the volatile oil of ginger plant on the shelf life of salmon fillets stored in refrigerator to reduce microbial growth, reduce chemical reactions, and increase the storage life of salmon fillets in refrigerator. Material and MethodsRainbow trout fish with an approximate weight of 600 grams were purchased from the market. Fish were washed with sterile distilled water, and cut into 60-gram pieces after separating the head and tail and eviscerating. The prepated fish were randomly divided into 4 groups. The control group was without any treatment but the treatment groups were immersed in chitosan containing different concentrations of Ginger essential oils. All the samples were kept in zipped bags at refrigerator (4°C) for 15 days. Microbial tests (Mesophilic, Psychrophilic, Coliform, and Lactic acid bacteria count), chemical tests (pH, TVN, TBARS), and sensory tests (color, smell, taste, texture, and overall acceptance) were performed on days 1, 4, 7, 12 and 15. The data obtained from the microbial and chemical tests were analyzed by one-way analysis of variance and the data obtained from the sensory tests were analyzed by the Kruskal-Wallis test in Sigma Stat 4 statistical software, considering P<0.05. Results and Discussion The results of bacterial tests showed that chitosan coating with ginger essential oil had a significant effect on reducing the growth of mesophilic, coliform, lactic acid bacteria and psychrophilic bacteria compared to the control and chitosangroups during 15 days of storage in the refrigerator (P<0.05). During the storage period, chitosan-treated groups containing 1.5% and 0.75% of ginger volatile oil had the best microbial quality in terms of mesophilic bacteria, Psychrophilic bacteria, lactic acid- bacteria, and coliforms. Also, in samples immersed in chitosan coating with ginger essential oil, the pH, TVN and TBARS values at the end of the storage period were significantly lower than the control and chitosan group (P<0.05). The results showed that pH, TVN, and TBARS did not exceed the defined standard for fish meat at the end of the storage period in the groups treated with ginger volatile oil. Sensory characteristicsindicated that the groups treated with chitosan coating containing ginger essential oils showed better sensory characteristics in terms of color, taste, smell, texture, and overall acceptance than the control and chitosan groups during the storage period (P<0.05). ConclusionBased on the results of the present study using the chitosan coating combined with ginger volatile oils has antimicrobial and antioxidant properties, which can reduce the oxidation of fats and microbial loads, while maintaining the organoleptic quality and increasing the shelf life of fish meat at refrigerator temperature. In comparison between treated groups, the use of chitosan along with 0.75% volatile oil of ginger is recommended, because by using a smaller amount of volatile oil, the microbial, chemical, and organoleptic properties can be kept at the standard level until the 15th day. Acknowledgments The authors are grateful to Shahrekord University's Research Vice-Chancellor for supporting this project.