Stability of Roselle, Lac and Gardenia colors in micellar systems

Abstract

Natural colors were used in place of synthetic colors because of low toxicity. However, limitation of using natural colors is due to their stabilities. This research intends to study changes and stabilities of three natural water-soluble colors; i.e. roselle petal, lac stick, and gardenia fruit in 3 micellar systems; i.e. sodium dodecylsulphate or SDS (anionic surfactant), cetyltrimetylammonium bromide or CTAB (cationic surfactant), and Tween80 (non-ionic surfactant) at concentration of 1, 5, 10, and 15 folds of their CMC values. Physicochemical characteristics of the extracted dyes were evaluated using several techniques including visible spectroscopy, pKa determination, HPLC, and LC-MS. Preliminary stability under six conditions (water, temperature, acid, base, oxidation, and UV light) and color stability in micellar systems were monitored by spectroscopy technique in terms of color intensity, color density, and percentage of color remaining at various times and CIELab system. The maximum wavelengths (λmax) of roselle, lac, and gardenia colors were 528, 490, and 443 nm corresponding to visualized colors of red, orange, and yellow, respectively. The apparent pKa of roselle and lac dyes were 3.00 ± 0.08 and 5.96 ± 0.15, respectively. HPLC and LC-MS showed that roselle dye composed of delphinidin-3-sambubioside and cyanidin-3-sambubioside as major coloring. Lac dye was a mixtures of laccaic acid A, B, and C, while the major components of gardenia dye were crocin, crocetin monogentiobiosyl monoglucosyl ester, and crocetin monogentiobiosyl ester. Roselle dye was unstable in alkaline, at elevated temperature, under oxidation, and under UV light. Lac color was unstable in alkaline, under oxidation and under UV light, while gardenia color was unstable in all conditions. Stabilities of roselle and lac dyes in micellar systems were in an order of in buffer > Tween80 micelles > SDS micelles while the color stability of gardenia was in an order of in SDS micelles > buffer > Tween80 micelles. Evaluation of color and color changes using UV-visible spectroscopy and CIELab system gave consistent results to one another. Visible spectroscopy clearly shows interaction between dyes and micelles but cannot describe observed color in details. CIELab system is a better way in describing color quality but cannot demonstrate dye and micelle interactions.