リソゾ-ム酵素活性を指標とする解凍魚と非凍結魚の鑑別法の検討

概要

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Lysosomal enzymes are released when lysosomal particles are ruptured by freezing-thawing. This study is concerned with whether or not frozen-thawed fishes can be differentiated from un-frozen ones by the activity level of lysosomal enzymes in the press juice of the muscle. The press juice were squeezed from unfrozen fish muscle and frozen-thawed one by centri-fugation, and the extracts were prepared by homogenizing the squeezed meat remained after centrifugation with 1% NaCl solution. The press juices and the extracts were used for deter-mination of the activities of lysosomal enzymes: β-N-acetylglucosaminidase, α-glucosidase, and cathepsin D. For each of the three enzymes, the ratio of the activity in the press juice to toal activity (the sum of the enzyme activities in the press juice and the extract) in frozen-thawed muscle was compared with that of the unfrozen one. Seven fish species were tested for the ratio. Theactivity ratio was increased by freezing-thawing by two to three fold, higher than that of the unfrozen muscle for the five species examined and by more than ten fold higher for the two species examined. It was, however, rather difficult to find out a standard level of the activity ratio adequate for differentiation of the frozen-thawed muscle from unfrozen muscle of various species of fish because the activity ratio varied considerably from species to species.