Identification of phenolic compounds isolated from pigmented rices and their aldose reductase inhibitory activities

Two anthocyanins (cyanidin-3-O-β-glucoside and peonidin-3-O-β-glucoside) and other phenolic (ferulic acid) were, respectively isolated from black and pigmented brown rices (Oryza sativa L. japonica) and their complete structures were determined by spectroscopic analyses (H NMR, C NMR and MALDI MASS). The HPLC profile of anthocyanins extracted from black rice showed cyanidin-3-O-β-glucoside as the first peak (85%) and peonidin 3-O-β-d-glucoside as the second (15%), while that of pigmented brown rice showed ferulic acid as the first peak (85.7%) and tocols as the second (14.3%). Several tocols were isolated and identified from the unsaponifiable fractions of both rices having some difference on their structures and amounts. The aldose reductase inhibitory activity of isolated compounds was in the following decreasing order: cyanidin-3-glucoside > quercetin > ferulic acid > peonidin-3-glucoside > tocopherol.All isolated compounds showed significant inhibitory activity against aldose reductase suggesting that both pigmented rices might contribute significantly in combating diabetic complications as health-promoting food ingredients in food processing.