Effect of vacuum packaging and low-dose irradiation on the microbial, chemical and sensory characteristics of chub mackerel (Scomber japonicus).

The effects of vacuum packaging followed by gamma irradiation treatment (1.5 kGy) on the shelf-life of fillets of chub mackerel (Scomber japonicus) were examined, during chill storage. The control and the treated packs were analyzed periodically for chemical (TMA, TBARS, biogenic amines) and microbial characteristics. Based on chemical and microbial data, vacuum packaging - by itself - was improper in extending the shelf-life of chub mackerel, estimated to 7 days. On the 7th day, TMA and Histamine contents reached the defect action levels, associated with the presence of mesophiles (3.7 log UFC/g); total coliforms (3.5 log UFC/g); staphylococci (1.9 log UFC/g) and the emergence of Pseudomonas (1.7 log UFC/g), in both the control and the vacuum packaged lots. Combination of vacuum packaging and gamma-irradiation was found to delay the spoilage during 14 days of refrigerated storage, based on chemical and microbial analyses. Similarly, consumer hedonic tests were performed to determine the effect of different treatments on the taste of fish fillets. For all treatments, consumers failed to discriminate treated samples from the control, on the 2nd day of storage (p > 0.05). The acceptability test showed that low-dose irradiation (1.5 kGy) optimised the sensory quality, on the 3rd day of storage (p < 0.05). The employment of vacuum packaging combined to a low-dose gamma-irradiation (1.5 kGy) on chub mackerel is recommended to enhance microbiological quality (4 log reduction), alleviate chemical changes and extend the shelf-life by 7 days, leading to consumer appreciation of these products.