Photo-stability of Mixture of Violet Pigments Phycoerythrin and Phycocyanin Extracted without Separation from Discolored Nori Seaweed

Water-soluble pigment mixture was extracted from discolored nori seaweed without separating phycoerythrin (PE) and phycocyanin (PC). The stability of this mixture against light irradiation was studied for application as a violet food coloring additive. The PC component showed greater photo-stability than the PE component of the pigment solution (pH 7.0, 20°C) under irradiation at 5,300 and 7,800 Lx. The ratio of the second-order rate constant kPE/kPC which reflects photo-destruction was 9.3 (5,300 Lx) and 7.0 (7,800 Lx). The results were similar to those of a respective pigment separated by gel-chromatography. As for tonal changes, the a* value was decreased and both the b* and L* values were increased with progressing photo-destruction, namely, the violet color changed to pale dark-violet due to de-coloration of the red PE component. A reduction in photo-fading of 6.6% (PE) and 6.9% (PC) was achieved by 7,800 Lx irradiation for 5 h, compared with the control, by adding γ-cyclodextrin to the mixture.