Effects of gamma irradiation on sensory, chemical and microbiological quality of smoked rainbow trout (Oncorhynchus mykiss) fillets

In this study, the effects of gamma irradiation at different doses (3 and 5 kGy) on the chemical, microbiological and sensorial quality of smoked, vacuum packed rainbow trout fillets during cold storage (2 °C) were investigated. The proximate composition of the smoked rainbow trout fillets were determined as 68.82 % for moisture, 3.04 % for ash, 23.53% for crude protein and 3.12 % for lipid. In all groups, the major fatty acids of smoked trout fillets were identified as palmitic acid, oleic acid, linoleic acid and docosahexaenoic acid (DHA) . The fatty acid compositions was not affected by the irradiation process initially. However, the increase in value on the total saturated fatty acids (SFA) of irradiated fillets has been found to be higher than the control group at the end of the storage. Fluctuations were observed in total monounsaturated fatty acids (MUFA) during storage. While a significant decrease was observed in the control group of total polyunsaturated fatty acids (PUFA), no change was observed in the groups irradiated with 3 and 5 kGy doses at the end of the storage. The quality parameters of pH and total volatile basic nitrogen (TVB-N) values were affected by the irradiation process and these parameters were found to be lower in irradiated groups compared to the control groups during storage. At the end of the storage, the pH values of control, 3 and 5 kGy irradiated groups were found to be 6.81, 6.70 and 6.67, respectively and the TVB-N values were 27.12, 25.47 and 24.46 mg/100g, respectively. However an opposite situation was observed with the thiobarbituric acid (TBA), peroxide (PV) and free fatty acid (FFA) values and increases in these values associated with the irradiation doses were determined. The TBA values of the control, 3 and 5 kGy irradiated groups were found to be 1.27, 1.46 and 1.58 mg MA / kg, respectively, the PV values were 6.12, 9.18 and 9.97 meq / kg and the FFA values were 5.36%, 5.67% and 6.10% (% oleic acid), respectively, at the end of the storage. It was determined that Enterobactericeae and E. coli were completely eliminated by the irradiation. Irradiation process was observed to have significant effects on total aerobic mesophilic bacteria (TVC) and total psychrophilic bacteria. Irradiation at both doses were also observed to have some significant impacts on hydrogen sulfide producing bacteria and lactic acid bacteria (LAB). While the TVC values of the control, 3 and 5 kGy irradiated groups were found to be 6.16, 5.51 and 5.71 log cfu/g, the total psychrophilic bacteria values were found as 6.71, 5.93 and 5.78 log cfu/g, respectively, at the end of the storage. According to the sensory evaluation, the shelf life of the control group was found to be 20 weeks while groups irradiated with 3 and 5 kGy doses were 23 weeks. No significant differences on the shelf life were observed between groups irradiated with 3 and 5 kGy doses. In this study, it was observed that sensory assessment results have supported by the chemical and microbiological analyses.