The total anthocyanin content (TAC) was
determined by the pH-differential method (Giusti
and Wrolstad, 2001). Anthocyanin pigments undergo
reversible structural transformations with a change
in pH manifested by strikingly different absorbance
spectra. The colored oxonium form predominates at
pH 1.0 and the colorless hemiketal form at pH 4.5. The
pH-differential method is based on this reaction, and
permits accurate and rapid measurement of the total
anthocyanins, even in the presence of polymerized
degraded pigments and other interfering compounds.