Biochemical factors influencing metmyoglobin formation in beef muscles.

To explain the different rates of metmyoglobin accumulation in bovine muscles, biochemical factors such as oxygen consumption rate, cytochrome a(+a(3)) content, myoglobin autoxidation and enzymic ferrimyoglobin reduction were studied. The measurements involved five cows and five bulls. Only six cows were used for Metmyoglobin Reducing Activity (MRA) measurements. Three muscles with different colour stability (Tensor fasciae latae, Psoas major and Diaphragma medialis) were chosen. Meat colour stability, as well as the oxido-reduction potential of myoglobin, were highly related to muscle type. The animal effect was low or non-significant. Muscles with the poorest colour stability, such as Psoas major and Diaphragma medialis had the highest oxidative activities (oxygen consumption rate) and the highest myoglobin autoxidation rates. Enzymic ferrimyoglobin reduction, estimated either by spectrophotometric measurements from muscle homogenates in aerobic conditions ('Metmyoglobin Reductase Activity') or by reflectance measurements in anaerobic conditions (MRA), does not explain the differences observed in muscle colour stability.