Abstract: In order to analyze the effect of temperature fluctuation on the quality of big-eye tuna (Thunnus obesus) during low-temperature circulation, changes in texture properties, pH, metmyoglobin (MetMb) content, total volatile basic nitrogen (TVB-N) content, histamine content, total viable count (TVC) and sensory evaluation score were measured during simulated cold chain logistics with constant (control) and fluctuating temperatures (L1: supermarket direct marketing; L2: supermarket retailing). The results showed that pH, MetMb content, TVB-N content, histamine content and TVC rose during the experimental period for all groups. The temperature fluctuation in group L2 was the most obvious compared with the other groups, and group L2 showed the most significant increase in hardness and chewiness as well as the most obvious quality deterioration. After 216 h, the pH of group L2 was as high as 6.66 and the MetMb content was increased up to 35.23%, indicating severe browning. In addition, the TVB-N content was 19.14 mg/100 g, histamine content 89.97 mg/kg, TVC 5.43 (lg (CFU/g)), and sensory score ?2 points. Correlation analysis demonstrated that the MetMb content, TVB-N content, histamine content and TVC were positively correlated with each other for all groups (P < 0.01 or P < 0.05), which could therefore be used to evaluate the quality changes of big-eye tuna during low temperature circulation. Conclusively, temperature fluctuations should be reduced as much as possible during circulation. Particularly, severe temperature fluctuations could affect the quality of big-eye tuna greatly.

Key words: temperature fluctuation; big-eye tuna; low-temperature circulation; quality