Determination of Anthocyanin Content. Monomeric anthocyanin content of the apple peels was measured using a spectophotometric pH differential protocol (23, 24). The apple peel extracts were mixed thoroughly with 0.025 M potassium chloride pH 1 buffer in 1:3 or 1:8 ratio of extract to buffer. The absorbance of the mixture was then measured at 515 and 700 nm against a distilled water blank. The apple peel extracts were then combined similarly with sodium acetate buffer pH 4.5, and the absorbance of these solutions was measured at the same wavelengths. The anthocyanin content was calculated as follows:
where A is absorbance = (A515 − A700)pH 1.0 − (A515 − A700)pH 4.5; MW is molecular weight for cyanidin 3-glucoside = 449.2; ε is the molar absorptivity of cyanidin 3-glucoside = 26 900; and C is the concentration of the buffer in milligrams per milliliter. Anthocyanin content was expressed as milligrams of cyanidin 3-glucoside equivalents per 100 g of fresh apple peel for the tripicate extracts.