INFLUENCE OF pH VALUE ON HUE ANGLE AND VISIBLE ABSORPTION MAXIMA OF CYANIDIN 3-O-beta-GLUCOPYRANOSIDE IN AQUEOUS SOLUTION

Cyanidin 3-O-beta-glucopyranoside (Cy3Glc) is a simple anthocyanin that is found in different berries, such as elderberries, blueberries, cowberries, whortleberries, blackcurrants, and black chokeberries. These are natural, water soluble, non-toxic pigments that can show a variety of colours, from orange to blue. Today, there is considerable interest in the development of food colorants from natural sources to replace synthetic food colorants. The aim of the study was to compare visible absorbance maximum (lambda(max-vis)) values of Cy3Glc aqueous solution at the various pH values with the corresponding hue angle (h(ab)) values. These facts are important from the viewpoint of the possibility to use these compounds as natural food colorants. The Cy3Glc aqueous solution was subjected to spectroscopic and colorimetric study to examine influence of pH value on h(ab) and lambda(max-vis). The h(ab) and the lambda(max-vis) in the aqueous solutions of Cy3Glc were studied across the whole pH range (from pH 0.5 to 13). Measurement of the h(ab) and the lambda(max-vis) showed that their values were highly dependent on the pH. For the Cy3Glc starting basic orange nuances is remained in area of orange hues with pH increase until pH until 3.34, and then with further pH increase colour of Cy3Glc gradually changed toward reddish nuances. At pH 6.98, the hue angles of Cy3Glc starting increase and consequently colour of solution changes from orange toward yellow at pH 9.46. In pH range 9.97-10.47 Cy3Glc had a yellow colour. At higher pH values, the hue angles increase again, and the colours gradually changed toward more yellowish green tones. For the lambda(max-vis) the following tendency was was observed: as pH increased, the lambda(max-vis) values of Cy3Glc showed the bathochromic shift. The lambda(max-vis) of Cy3Glc aqueous solution shifted from 508 nm (at pH 0.50) to 603 nm (at pH 12.53). The solution of Cy3Glc exhibited variations of h(ab), although their lambda(max-vis) remained stable. By contrast, solutions having shifted spectra share the same basic tonality. The lambda(max-vis) values of Cy3Glc aqueous solution at the various pH values correlated poorly with the corresponding h(ab) values and caution should be applied when using lambda(max-vis) values for interpretation of colours.