2.4. Determination of total anthocyanin content (TAC)
The TAC was determined using a spectrophotometric pH differential method (Giusti & Wrolstad, 2001) with some modifications. Two dilutions were performed for each sample, one with hydrochloric acid–potassium chloride buffer (0.025 M, pH 1.0) and the other with sodium acetate buffer (0.4 M, pH 4.5). Difference in absorbance of the two dilutions at different pH values is caused by a structural transformation of the constituent anthocyanins from the coloured oxonium at pH 1.0 to the colourless hemiketal at pH 4.5 (Giusti & Wrolstad, 2001). Samples were diluted to allow the absorbance readings to be in the linear range (