Anti-oxidant capacities of flavonoid compounds isolated from acai pulp (Euterpe oleracea Mart.)
Acai fruit (Euterpe oleracea Mart.) has been demonstrated to exhibit extremely high anti-oxidant capacity. Seven major flavonoids were isolated from freeze-dried acai pulp by various chromatographic methods. Their structures were elucidated as orientin (1), homoorientin (2), vitexin (3), luteolin (4), chrysoeriol (5), quercetin (6), and dihydrokaempferol (7) by NMR, MS and compared with the reported literature. Compounds 3 and 6 were reported from acai pulp for the first time. Anti-oxidant capacities of these flavonoids were evaluated by oxygen radical absorbance capacity (ORAC) assay, cell-based anti-oxidant protection (CAP-e) assay and reactive oxygen species (ROS) formation in polymorphonuclear (PMN) cells (ROS PMN assay). ORAC values varied distinctly (1420–14,800 µmol TE/g) among the seven compounds based on numbers and positions of hydroxyl groups and/or other substitute groups. The ORAC values of aglycones are generally higher than that of glycosides. CAP-e results indicated that only three compounds (4, 6 and 7) could enter the cytosol and contribute to the reduction of oxidative damage within the cell. The ROS PMN assay showed that five compounds (2–3 and 5–7) demonstrated exceptional effects by reducing ROS formation in PMN cells, which produced high amounts of ROS under oxidative stress. In evaluating the anti-oxidant capacity of natural products, combining both chemical and cell-based assays will provide more comprehensive understanding of anti-oxidant effects and potential biological relevance.