Effect of met-myoglobin reductase on the color stability of blue fin tuna during refrigerated storage

ABSTRACT: To investigate the reducing ability of met-myoglobin (metMb) reductase, browned tuna meat was immersed with/without metMb reductase (0.103 unit/mL) for 120 min at 4°C. The metMb reductase activity of browned tuna meat significantly increased, whereas no significant change was observed in the control sample for the first 10 min of immersion ( P > 0.05). After comparing the changes in metMb reductase activity, metMb content, Hunter's 'a' and color, it was observed that the reductase did recover the bright red color. To further confirm the role of metMb reductase in color stability, fresh tuna meat was first immersed in metMb reductase (0.503 unit/mL) or a mixture of reductase and nicotinamide adenine dinucleotide (NADH) (1 mM) solutions at 5°C for 10 min, and then stored at 4°C and relative humidity 100%. No significant changes in metMb accumulation and in metMb reductase activity were observed between samples treated with enzyme alone and enzyme + NADPH ( P > 0.05). Changes in metMb reductase activity, metMb, Hunter's 'a' value and color for both the control and treated samples suggested that immersion in metMb reductase could extend the color stability of tuna meat, and that the enzymatic reduction of metMb by its reductase occurred during refrigerated storage.