Effects of temperature changes on freshness of tuna ( Thunnus obesus) fillet in cold chain logistics

To investigate the effect of temperature variation on quality and microstructure of tuna ( Thunnus obesus) when transported, changes in pH value, metmyoglobin formation, thiobarbituric values ( TBA) , total volatile basic nitrogen ( TVB-N) , trimethylamine nitrogen ( TMA-N) , histamine and microbiological were assayed periodically in 3diverse simulated situations of logistics.The results showed that the freshness of bigeye tuna stored in ultra- low temperature was significantly affected by temperature changes in the logistics process.Freshness of tuna could be maintained under complete cold chain of-55℃ during transportation and sale, while the more the frequency and range of temperature changes, the greater the deterioration would be. When transported at- 18℃ twice before stored at 4℃ in domestic refrigerators for 12 hours, pH value, metmyoglobin percentage, thiobarbituric values of the tuna were 6.71, 64.77%, 1.277mg malonaldehyde /kg respectively.Although TVB-N, TMA-N and TVC of tuna didn't exceed the legal limits, it had lower freshness than those maintained at-18℃ all the time.Histamine of tuna during storage did not change significantly, so all experimental groups were in the safe range. The lack of ultra- low temperature refrigerated trucks would result in lower freshness of fish. Therefore, temperature variation between transportation and storage should be avoided.In general, this study is going to provide reference for retaining the freshness of tuna in stages of storage, transportation and sale.