Relation between Freshness of Antarctic Krill and Extractability of Its Muscular Protein

The extractability and its biochemical properties of muscular protein with 0.45 M NaCl phosphate buffer from washed muscle, free from digestive enzymes, have been studied in relation to freshness of muscle of Antarctic krill Euphausia superba. To extract a large portion of muscular protein from the fresh muscle obtained from the krill immediately after death, it was necessary to homogenize the muscle with 0.45M NaC1-pho sphate buffer (pH 7.0-7.5, I••0.5) for 30 seconds retaining the temperature below 10•Ž. The extractable protein thus obtained amounted to over 90% on the basis of total protein in the homo genate but its ATP-sensitivity as well as viscosity number was very low. With the lapse in the storage at 2•Ž, the amount of the extractable protein first decreased and then increased to the same level of that from the fresh muscle. During this period, ATP sensitivity and viscosity number of the extracted protein were increased and remained at the maxi mum values. As the high ATP content in the fresh muscle was reduced with the lapse of time, the extractable protein was concomitantly decreased. In addition, it was recognized that the addition of ATP in the extraction medium remarkably increased the amount of extractable protein from the muscle containing poor ATP. These results revealed that not only the quantity but also the quality of the extractable protein from the muscle was strongly affected by the freshness of krill.