The colour property of natural anthocyanins, described as
absorption spectra, was evaluated in the pH range of 1–8 (Fig. 1).
The results indicated that the absorbance values at maximum
absorption wavelength decreased with increasing pH up to pH 6.
The high absorbance values were observed only at pH 1–2 and
the colour of anthocyanins was strong red. At pH 3, the colour of
solution was fading and the decreasing of absorbance was found
sharply at pH 4–6. With increasing pH, flavylium cation (red) concentration
decreases as hydration to the colourless carbinol or
pseudobase occurs, which then equilibrated to the open chalcone
form (Mazza & Brouillard, 1987). Furthermore, the higher absorptions
were found between 570 until 600 nm at pH 7–8, due to
the presence of unstable blue quinonoidal structures. The bathochromic
shifts were also observed at pH > 4.