Cold pasteurization of Rainbow Trout fillet (Oncorhynchus mykiss) with gamma rays and shelf Life assessment at refrigerated condition

The present study was conducted to evaluate the effect of different doses of gamma rays on shelf life and fatty acids composition of Rainbow trout fillet (Oncorhynchus mykiss) during refrigerating condition. Quality and shelf life of non-irradiated and irradiated (0, 0.75, 1.5, 2.25, 3, 3.75 and 4.5 kGy) Rainbow trout stored at +4 C was investigated by measurement of microbiological, chemical and sensory analysis .Irradiation of fillets was performed by gamma rays from a Co60 source. Microbial counts for non-irradiated trout fillet samples were higher than respective irradiated fish. Total volatile base nitrogen (TVB-N) values was increased from 7 mg/100 g for non-irradiated to 52.7 mg/100 g after 15 days storage at refrigerator, whereas for irradiated fish lower values of 39.4, 37.6, 28.7, 25.6, 24.8 and 23.2 mg/100 g were recorded at 0.75, 1.5, 2.25, 3, 3.75 and 4.5 kGy, respectively (day 15).initial amount of peroxide value in non irradiated sampleswas 0.8 meq/kg and was increased to 7 meq/kg (7 day).Highest amount of peroxide after irradiation process was belonged to samples irradiated by 4.5 kGy (1.5 meq/kg). Also, total viable count of irradiated samples were decreased significantly (p<0.05). On nutritional aspect, results showed that total saturated fatty acid concentrations increased significantly (p<0.001) with increasing irradiation dose , so that the control sample and fish muscles that irradiated with 4.5 kGy had the lowest and highest amounts of total saturated fatty acids (20.454 ± 0.011% and 19.228 ± 0.040% , respectively). The amount of total polyunsaturated fatty acids (PUFAs) in irradiated samples were significantly lower than control sample (p<0.001) and amounts of total monounsaturated (MUFAs) were significantly higher than control samples (p<0.001). The results were indicated that the highest content of MUFAs and PUFAs were in samples irradiated with 3.75kGy (37.783± 0.092 %) and control samples (37.677± 0.104 %), respectively .The lowest level of MUFAs and PUFAs were in control samples (36.596 ± 0.024%) and 4.5 kGy (36.459 ± 0.047%), respectively. Altogether, results of this study were determined that irradiation treatment changes significantly the fatty acid composition especially polyunsaturated fatty acids in rainbow trout muscle (P<0.001). Overall, irradiation of fillet by 3.75 kGy had best results on increasing shelf life of fillet at refrigerator (between 11-15 days) and had no advers effect on fatty acid composition of Rainbo trout fillet.

Iranian Fisheries Science Research Institute

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