Effect of Freezing and Thawing on the Quality of Northern Bluefin Tuna Thunnus Thynnus (Linnaeus 1758)

Abstract

Global tuna populations are in decline. Maintaining post-catch fish quality is important to prevent wastage of precious food resources. Tuna is often preserved by freezing; however, changes in tuna quality post-thawing have been poorly investigated. Therefore, the aim of this study was to evaluate the quality of frozen/thawed and raw flesh of northern bluefin tuna Thunnus thynnus (Linnaeus 1758) over 7 or 8 days period using characteristic indicators of flesh quality such as colour, bacterial count, K-value, pH and odour. The results showed that colour was significantly influenced by freezing and thawing. The colour of thawed tuna flesh deteriorated after 3 days, while that of raw flesh was maintained for 6 days. In contrast, bacterial count, K-value, pH and odour were not significantly influenced by freezing and thawing. The K-value was approximately 20% after 3 days at 4 °C in both raw and frozen/thawed flesh. Tuna should not be eaten raw if it was stored for longer than 3 days at 4 °C, regardless of whether the tuna was frozen and then thawed or kept raw. Freezing preserves the quality of fish flesh for a long period and is thus a good strategy to prevent tuna spoilage.