Influence of pH on color variation and stability of cyanidin and cyanidin 3-<i>O-β</i>-glucopyranoside in aqueous solution

Abstract

Changes in color and color stability of cyanidin and cyanidin 3-O-β-glucopyranoside (Cy3Glc) in aqueous solutions were investigated at pHs from 0.5 to 13.1, by combination of colorimetry and spectrophotometry. The glucosidic substitution at C-3 of cyanidin (i.e., Cy3Glc), moved the tonalities toward the yellow pole of the chromatic circle, which resulted in high Chroma increases and a hypsochromically shifted visible absorbance maximum (λmax-vis). Under the most acidic and alkaline conditions, cyanidin showed greater Lightness compared with the rest of the pH range. At these extreme pHs, the lower Lightness of Cy3Glc was coupled with a high Chroma value. As a consequence, Cy3Glc showed its most intense color under the most acidic and alkaline conditions, and did not show visually perceptible color at neutral pH. At pH <3 and from pH 10 to11 cyanidin had lower color stability than Cy3Glc. We show the correlations between the data for these color and stability variations for cyanidin and Cy3Glc over the entire pH range.