Studies on the application of thin layer isoelectric focusing to food analysis II. Identification of fish species by numerical value of isoelectric focusing pattern.

Abstract

For the biological identification of fish species by electrophoresis including isoelectric focusing (Y. Ukishima, et al., Eisei kagaku, 30, 189 (1984)) of the sarcoplasmic proteins, it is generally required to electrophoresize the standard samples together with the test samples. However, each standard sample is not always kept in the laboratories. We, therefore, attempted to identify fish species, without standard samples, by applying numerical values which indicate isoelectric focusing patterns of sarcoplasmic proteins. To determine the pH gradient of polyacrylamide gel, a method with pI markers was more satisfactory in the reproducibility and operability than the methods with pH micro electrode. The stained protein bands on isoelectro-focused polyacrylamide gels were scanned by a densitometer, and pI values and relative peak heights of the five to ten bands were numerically expressed. Relative standard deviations of pI values of the protein bands were below 1%. Isoelectro-focused sarcoplasmic protein bands of 45 fish species were also numerically expressed. The numerical values were species-specific except bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares), indicating that fish species are successfully identified by using the tables of numerical values of isoelectro-focused sarcoplasmic proteins. Furthermore, isoelectro-focused sarcoplasmic proteins of seasoned fish slices were numerically expressed. Although a few protein bands were disappeared or weakened by seasoning process, the present identification method might also be applicable to the seasoned slice samples.