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

To investigate the reducing ability of met-myoglobin (metMb) reductase, bro wned tuna meat was immersed with/without metMb reductase (0.103 unit/mL) fo r 120 min at 4 degreesC. 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 co lor, it was observed that the reductase did recover the bright red color. T o further confirm the role of metMb reductase in color stability, fresh tun a meat was first immersed in metMb reductase (0.503 unit/mL) or a mixture o f reductase and nicotinamicle adenine dinucleotide (NADH) (1 mM) solutions at 5 degreesC for 10 min, and then stored at 4 degreesC and relative humidi ty 100%. No significant changes in metMb accumulation and in metMb reductas e activity were observed between samples treated with enzyme alone and enzy me +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 i mmersion 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.