Change in color and quality of tuna during treatment with carbon monoxide gas

Abstract

The yellowfin tuna steaks (ca. 8 × 5 × 2 cm) sealed in a package and treated with 99.5% carbon monoxide (CO) gas at 4°C for 5 days were compared with the control steaks without CO gas treatment stored at same condition. The surface layer (2 mm thick), middle layer (2 ∼ 4 mm from surface) and inner layer (4∼6 mm from surface) were separately cut from the fish steak. For each layer, the Hunter's color value (L, a, b), metmyoglobin formation (metMb%), volatile basic nitrogen (VBN) and CO residue were measured and compared. The results revealed that Hunter +a value of tuna steaks treated with CO gas for 4 hr increased higher than that of the control steak for all three layers. However the values of L and +b between the CO gas-treated steak and the control steak differed slightly. The metMb% in the surface layer showed no significant difference with or without the CO treatment whereas the metMb% in the middle and inner layers of CO gas-treated steak were apparently lower than that of the control steak. The VBN of the steaks remained below 20 mg/100 g during the 5-day chilling storage regardless of CO gas treatment. The amount of CO residue in the surface layer increased rapidly in 24 hr of the treatment and consequently reached the highest value at 96 hr, while those in the middle and inner layers increased quickly in 48 hr. The CO residue in the inner layer remained constant after 48 hr of treatment at a value about a half as high as that in the surface layer.