Comparison of several correlations include one utilizing soret band for spectrophotometric determination of metmyoglobin in tuna meat extracts.

The red colour of meat is an important factor used in the evaluation of tuna meat quality, and strongly influences the consumer’s purchasing decision. It is known that the meat colour of tuna is dependent on the degree of oxidation of Myoglobin (Mb) included in muscular cells of red meat. When the iron ion is in the ferric state it becomes metmyoglobin (metMb) which appears as brown meat colour. Because Mb oxidation was commonly reported in terms of the percentage of metMb (%metMb), it would be an important indicator to determine the meat quality. To determine %metMb, we often use UV spectrophotometer to measure the absorption of myoglobin extracts and then calculate the %metMb. There’re several previously reported equations, but different %metMb values would be obtained with the different equations. Also, all of the equations use the Q band (480-650nm) absorption. However, in the soret band (around 400nm), there’s also a characteristic peak, and the peak can be shifted during the oxidation of the Mb, which can be used to determine %metMb. In this study, we use different equations reported to calculate the %metMb of tuna meat, and compare the differences. In addition, we use a new equation which used soret band, and compare it with reported equations to prove its feasibility.