Bioactive components and antioxidant activities of oak cup crude extract and its four partially purified fractions by HPD-100 macroporous resin chromatography

Documents have revealed that leaves, barks and woods from oak trees are rich in phenols, yet little is known about them in Mongolian oak (Quercus mongolica) cups, the by-product waste with large biomass. In the present work, composition analysis through total phenols, flavonoids and tannins, and condensed tannins, and HPLC profiles and antioxidant assessment by DPPH, ABTS, reducing power, ORAC and CAA were performed to evaluate oak cup crude extracts and the resulting four fractions (Fr. I, Fr. II, Fr. III and Fr. IV) prepared by HPD-100 macroporous resin chromatography. Among the optimal 50% ethanol crude extract (ECE) and its subsequent four fractions, Fr. II, on the basis of the oak cups, collected the majority of total phenols, flavonoids and tannins, and condensed tannins from ECE though lower contents of all compositions than those in Fr. III when based on the extract with an exception of condensed tannins. And the highlight of Fr. II is that it possessed the strongest antioxidant ability from the perspective of extract. These findings imply that composition of condensed tannins as well as its contents might take dominate role in antioxidant ability of oak cups. This was further corroborated through HPLC profiles as compositions in ECE and the four fractions are all distinguished from each other. HPLC also exhibited the great enrichment of ellagic acid in Fr. III. Moreover, the correlation analysis indicated that there is exclusive correlation existed between total flavonoids and antioxidant assays among all composition analysis including ellagic acid, which further confirmed the main influencing factor to antioxidant ability of oak cup may be composition of condensed tannins as well as its contents because the condensed tannins were constituted by flavonoid units, and ellagic acid may not be a strong antioxidant contributor in oak cups. Therefore, Fr. II should be chosen as the best fraction to be further explored. In addition, this established HPD-100 macroporous resin chromatography procedure could be developed as a simple and effective procedure for preparation of ellagic acid from oak cups.