Comparative stability of dimeric and monomeric pigments extracted from sea urchin Strongylocentrotus droebachiensis.

Ultraviolet-visible spectroscopy and UPLC-DAD-MS were used for analysis of stability of ethanol solutions of ethylidene-6,6'-bis(2,3,7-trihydroxynaphthazarin) (ENZ), spinochrome dimer (SDM) and spinochrome D (SD) that were isolated from Strongylocentrotus droebachiensis. In the freshly prepared solution, the concentration of ENZ at pH 6.0 was at 6 fold less comparing to pH 1.6. The increase of pH up to 4.0 resulted to increase of SD concentration and to decrease of SDM concentration. After 48 h storage, both dimers showed the highest stability at pH 1.6, while the elevation of the pH solution up to 6.0 activates degradation of SDM and ENZ at 1.3 and 3.6 fold correspondingly. The concentration of SD after 48 h storage at the pH 1.6 was at two-fold less comparing to the initial concentration, and at the pH 6.0 - at 4 fold less. This study contributes to increasing the knowledge on the stability of the spinochrome pigments.