Phung Thi Tuyen, Do Tan Khang, Pham Thi Thu Ha, Tran Ngoc Hai, Abdelnaser Abdelghany Elzaawely, Tran Dang Xuan, Antioxidant Capacity and Phenolic Contents of Three Quercus Species, ILNS Volume 54, International Letters of Natural Sciences (Volume 54)
    The antioxidant capability and phenolic contents of ethanol extracts (free phenolics) and ethyl acetate extracts (bound phenolics) of three <i>Quercus</i> species were estimated in this work. The antioxidant activities were examined by 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) free radical, reducing power and <i>b</i>-carotene bleaching methods. HPLC was employed to detect major phenolic acids. The leaf extract of <i>Q. salicina</i> contained maximum total phenolics while the highest total flavonoid content was found in the leaf extract of<i> Q. serrata</i>. The antioxidant activities varied among three species. Bark extract of <i>Q. salicina</i> was the most potential and it was closed to levels of the standard antioxidative dibutyl hydroxytoluene (BHT). The bark extract of <i>Q. serrata</i> also showed promising antioxidant activities despite their eminence was negligibly lower than <i>Q. salicina</i>. Stronger antioxidant activities of free phenolics than those of the bound phenolics may be attributed to higher quantities of free phenolics in the barks of <i>Quercus</i> species, however total flavonoids may not contribute a critical role. By HPLC analysis, thirteen phenolic acids were detected in the leaf and bark extracts. Of them, <i>Q. salicina </i>showed maximum in number (ten compounds) and quantities of detected phenolic acids. Ellagic, chlorogenic and benzoic acids were dominant in <i>Quercus</i> species. Findings of this study revealed that leaves and barks of three <i>Quercus</i> species are rich source of antioxidants, and <i>Q.</i> <i>salicina</i> is the most promising and should be elaborated to exploit its pharmaceutical properties.
    Antioxidant Activity, Phenolic Compounds, <i>Quercus crispula</i>, <i>Quercus salicina</i>, <i>Quercus serrata</i>