Nippon Suisan Gakkaishi 76 (4), 695-704 (2010)

Changes in quality and denaturation of sarcoplasmic protein components in the burnt meat of bluefin tuna Thunnus thynnus orientalis

YOSHIHIRO OCHIAI*

Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, Tokyo 113-8657, Japan

Burnt meat or spontaneously done meat (“yake-niku” in Japanese), which is accompanied by meat quality deterioration such as whitish discoloration, decrease in water holding capacity, etc., occurs frequently to tunas, especially during the summer season. However, the mechanism behind this phenomenon has not yet been fully explained. So far there has been no objective criterion to evaluate the extent of tuna meat deterioration. In order to elucidate the properties of burnt meat in cultured and wild bluefin tuna, differences in the meat quality (metmyoglobin formation ratio, myoglobin content, color difference values) and water-soluble (sarcoplasmic) protein components in the ordinary (white) and dark muscles were compared between normal and burnt fish. The data obtained showed that aggregation and decomposition of protein components took place in the burnt meat. Since some components, such as creatine kinase in the ordinary muscle, were absent in the burnt portion irrespective of whether the fish was wild or cultured, they were found to be excellent markers to distinguish burnt fish from normal fish. On the other hand, the extent of changes in myoglobin was quite small based on the data of solubility and calorimetric analysis, suggesting that this protein is not largely involved in discoloration of burnt portions.


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