Studies on the extractive components of ascidians. I. Seasonal variation of extractive nitrogen and free amino acids in the muscle of the ascidian Halocynthia roretzi.

Abstract

Extractive nitrogen and free amino acids in the muscle of the cultured ascidian Halocynthia roretzi were analyzed on the specimens collected bimonthly from May 1980 to September 1981 at Okkirai Bay, Iwate Prefecture, and on the specimens collected in May and November 1980 at Onagawa Bay, Miyagi Prefecture, The ascidian muscles were rich in free amino acids, especially in taurine, proline, glutamic acid, glycine and alanine, but scanty in arginine, Most amino acids as well as extractive nitrogen showed a marked seasonal variation and lowest values were found in winter. Significant differences in some amino acids were observed between the specimens collected from the two localities in May. The ascidian seems to bear both characteristics of marine vertebrates and invertebrates with respect to the free amino acid composition of the muscle in line with its taxonomic position. It is suspected that the palatability of the ascidian muscle is closely related to the free amino acids, as their contents were considerably higher in the season when its flavor is better.