マグロ肉のmetmyoglobinの簡易測定法

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Generally there are three forms of myoglobin (Mb) in meat; reduced Mb, oxymyoglobin (MbO2) and metmyoglobin (MMb), and the discoloration of meat is caused mainly by the transformation of MbO2 to MMb. So the degree of discoloration of meat is shown by MMb content. Several authors have made the determination by spectrophotometrically using water extract of meat1)5)6). This report presents a simple method for the determination of MMb using opal glass apparatus9)10). It was found generally that tuna meat which was selled as a fillet contained Mb02 and MMb, and these absorption spectra have two isosbestic points at 520 and 590mμ, and have alpha and beta band at 575 and 540mμ, respectively. No shift can be seen on both absorption band at 540 mμ and isosbestic point at 520 mμ in different samples tested, while the alpha band at 575 mμ and the isosbestic point at 590 mμ were very often shifted within a few mμ's. Calculations were made by using E540 and E520 which were obtained by subtracting the tailing absorption value due to opal glass in the range of wavelength between 670 and 700 mμ. Using differently discolored samples the ratio (R) of the absorption value at 540mμ to cul-culated by the author's method were plotted against MMb contents determined by the method of Sano and Hashimoto6) and linear line is obtained. (Fig. 2) Thus the MMb content in commercial tuna meat fillets can be promptly determined from this figure and the ratio R which can be easily obtained within a few minutes with the aid of opal glass apparatus.