Effect of Freezing and Thawing on the Discoloration of Tuna Meat

Abstract

Discoloration profiles of unfrozen or frozen and thawed (“frozen/thawed”) meat of bluefin, yellowfin, and bigeye tunas during iced storage were examined, taking as parameters the metmyo-globin (metMb) to total Mb ratio (metMb%), solubility (extractability) of Mb, and Hunter color difference scale (L, a, and b values).
During storage, metMb% rapidly increased, while Mb solubility and a value remarkably decreased, L and b values tending to increase. Discoloration of frozen/thawed meat generally proceeded faster than that of unfrozen meat during iced storage, irrespective of tuna species. No significant differences in discoloration profile were observed among surface, middle and inner portions of dorsal meat, and ventral meat. Bigeye tuna meat showed a quite slow discoloration, even after freezing and thawing.
In the bluefin tuna meat which was pre-stored at -20° ?? -80°C for one month, followed by iced storage, the lower the pre-storage temperature was, the slower the rate of discoloration.