The acid-base equilibrium of these pigments were investigated using spectrophotometric and
potentiometric methods.
In the present study we have extracted the anthocyanin from rose flowers by 3
methods using methanolic solutions of 0.1% HCl, citric acid and tartaric acid.T he
anthocyanin was used as natural indicator in acid – base titration. The intrinsic pH of the
extract was 2.88. The spectroscopic data of the extracted anthocyanin pigments indicate a
shift in wavelength maxima of the colors by addition of stannous salt and the complex not
only showed change in pH of the aqueous medium but it also showed change in λmax. The
extract showed wavelength maxima change from 517 nm (dark pink) to 592 nm (green)
between the pH range 2 to 9. Significant changes were observed when stannous salt was
added to the rose anthocyanin extract.
The colorant present in the rose flower is mainly consisting of cyanidin, pelargonin
or peonidin or to mixtures of these pigments as shown in figure-1.