Determination of anthocyanins and proanthocyanidins (PAs) contents
Five grams of frozen fruit skin tissue without achenes were grounded with liquid nitrogen, homogenized with 15 ml of acetone/water (80/20 v/v) and stored at -20°C until use. Anthocyanins quantification was performed according to previously reported [42]. Briefly, 50 μl of fruit extract and 150 μl of corresponding buffer were dispensed into a 96-well plate. The absorbance was measured at 509 nm and 700 nm, considering ε = 17,330 L/cm1.mol1. The results were expressed as mg of pelargonidin-3-glucoside equivalents per 100 g of fresh weight (FW). PAs content was measured according to previously reported [43]. Briefly, 70 μl of fruit extract diluted (1/10, v/v) and 210 μl of dimethylaminocinnamaldehyde (DMAC) reagent were dispensed into wells of a 96-well plate. The microplate was read for 20 min at 640 nm. The concentration was calculated from a calibration curve, using catechin as standard. The results were expressed as mg of catechin equivalents per 100 g of FW.