Buffering capacity of free histidine and its related dipeptides in white and dark muscles of yellowfin tuna.

Abstract

A comparison of the difference between buffering capacrities of white and dark muscles of yellowfin tuna was made using β-pH curves, and the contribution of free histidine and its related dipeptides was investigated by means of omission test of the whole synthetic extract which was prepared by blending reagent grade chemicals on the basis of analytical values of the muscle ex-tract. The homogenate and picric acid extract of the white muscle showed higher buffering capac-ity than in the dark muscle, and the curve of the whole synthetic extract of the white muscle re-sembled that of a picric acid extract. When histidine and anserine, the most prominent nitrogenous compounds in the white muscle, were omitted, the buffering capacity was almost lost, and there-fore, these constituents were found to play the most important role in the buffering of the white muscle. In the dark muscle, these constituents, naturally, did not participate in the main buffering of the muscle, since it contained relatively low amounts of histidine and anserine.