Shelf-life extension of vacuum-packaged sea bream (Sparus aurata) fillets by combined γ-irradiation and refrigeration:: microbiological, chemical and sensory changes

The combined effect of gamma-irradiation and refrigeration on the shelf-fife of vacuum-packaged sea bream (Sparus aurata) fillets was studied by monitoring the microbiological, chemical and sensory changes of non-irradiated and irradiated fish samples using low-dose irradiation doses of 1 and 3 kGy. Fish species such as sea bream and sea bass are very popular in the Mediterranean countries due to their high quality characteristics, and their preservation is a constant challenge given their extreme perishability. Irradiation (3 kGy) dramatically reduced populations of bacteria, namely, total viable counts (3 vs 7 log cfu g(-1)) for the non-irradiated samples, Pseudomonas spp (< 2 vs 7.6 log cfu g(-1)), H2S-producing bacteria typical of Shewanella putrefaciens (< 2 vs 5.9 log cfu g(-1)), Enterobacteriaceae (< 2 vs 6.0 log cfu g(-1)) and lactic acid bacteria (< 2 vs 3.5 log cfu g(-1)) after 10 days of storage. The effect was more pronounced at the higher dose (3 kGy). Lactic acid bacteria, Enterobacteyiaceae and H2S-producing bacteria typical of Shewanella putrefaciens showed higher sensitivity to gamma-radiation than did the rest of the microbial species. Of the chemical indicators of spoilage, Trimethylamine (TMA) values of non-irradiated sea bream increased very slowly, whereas for irradiated samples significantly lower values were obtained reaching a final value of 7.9 and 6.3 mg N per 100 g muscle at 1 and 3 kGy respectively (day 42). Total volatile basic nitrogen (TVB-N) values increased slowly attaining a value of 67.3 mg N per 100 g for non-irradiated sea bream during refrigerated storage, whereas for irradiated fish, lower values of 52.8 and 43.1 mg N per 100 g muscle were recorded (day 42). Thiobarbituric acid (TBA) values for irradiated sea bream samples were higher than respective non-irradiated fish and increased slowly until day 21 of storage, reaching final values of 1.1 (non-irradiated), 2.0 (1 kGy) and 2.2 mg malonaldehyde kg(-1) muscle (3 kGy), respectively (day 42). Sensory evaluation showed a good correlation with bacterial populations. On the basis of overall acceptability scores (sensory evaluation) a shelf-life of 28 days (3 kGy) was obtained for vacuum-packaged sea bream, compared with a shelf-fife of 9-10 days for the non-irradiated sample. (c) 2004 Society of Chemical Industry.