2.4.4. Anthocyanins
Total monomeric anthocyanins (TMA) were determined using
the pH differential method of Giusti and Wrolstad (2001).
This method measures the absorbance at two pH values (pH 1 and 4.5)
and is based on the change in anthocyanin structure as a function
of pH. Absorbances were measured at 510 and 700 nm with a UV–
Vis spectrophotometer. The monomeric anthocyanin pigment was
expressed as cyanidin-3-glucoside units (mg/l). In addition, the
percentage of the colour contributed by polymerised anthocyanin-
tannin complexes was measured by exploiting the bleaching
reaction of monomeric anthocyanins by bisulfite (Giusti &
Wrolstad, 2001).