Metmyoglobin reducing activity in the mitochondrial fraction from the dark muscle of tuna

Abstract

Desirable bright cherry-red meat color of tuna depends on the redox state of myoglobin (Mb). Mitochondria involved in energy production in live muscle, also influence the redox state. However, no research has determined metmyoglobin (metMb) reduction in tuna muscle via mitochondria. This study aimed to assess the metMb reductase activity in the mitochondrial fraction from the dark muscle of tuna with a high concentration of Mb. As a result, elevated assay temperature resulted in increasing mitochondrial metMb reductase activity in the range of 10-30°C. There was no significant change in the activity between pH 5.7-6.8, but a significant decrease was observed at pH 7.0. Furthermore, NADH, as the cofactor, was found to initiate the metMb reduction, while exhaustion of NADH resulted in metMb formation. Therefore, maintenance of NADH concentration was considered to be essential to maintain the color of tuna meat during chilled storage.