Abstract:Bluefin tuna (Thunnus thynnus) meat, wrapped with or without polyethylene film, was stored at 4°C and relative humidity of 100%. Decrease in Hunter’s ‘a’ and increase in ‘L’ were observed in both samples during 120 h storage. Metmyoglobin (metMb) reductase activity of both samples decreased, while the metMb increased with the duration of storage. The nicotinamide adenine dinucleotide (NADH) of tuna meat increased during the first 56–80 h of storage, but decreased again during the further storage. Although the nicotinamide adenine dinucleotide phosphate (NADPH) of both wrapped and unwrapped samples decreased with the duration of storage, the total amount of NADH and NADPH seemed to remain at a constant level during the first 80 h storage and then significantly decreased during further storage. The metMb reductase is an important factor affecting the accumulation of metMb of refrigerated tuna.