Hindawi Publishing Corporation Evidence-Based Complementary and Alternative Medicine Volume 2012, Article ID 215959, 8 pages doi:10.1155/2012/215959 Research Article Antioxidant Activities and Phytochemical Study of Leaf Extracts from 18 Indigenous Tree Species in Taiwan Shang-Tse Ho, 1 Yu-Tang Tung, 2 Yong-Long Chen, 1 Ying-Ying Zhao, 1 Min-Jay Chung, 3 and Jyh-Horng Wu 1 1 Department of Forestry, National Chung Hsing University, Taichung 402, Taiwan 2 Department of Life Sciences, National Chung Hsing University, Taichung 402, Taiwan 3 The Experimental Forest, National Taiwan University, Taipei 106, Taiwan Correspondence should be addressed to Jyh-Horng Wu, eric@nchu.edu.tw Received 30 June 2011; Accepted 25 October 2011 Academic Editor: Virginia S. Martino Copyright © 2012 Shang-Tse Ho et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The objective of this study is to assess antioxidant activities of methanolic extracts from the leaves of 18 indigenous tree species in Taiwan. Results revealed that, among 18 species, Acer oliverianum exhibited the best free radical scavenging activities. The IC 50 values were 5.8 and 11.8 μg/mL on DPPH radical and superoxide radical scavenging activities, respectively. In addition, A. olive- rianum also exhibited the strongest ferrous ion chelating activity. Based on a bioactivity-guided isolation principle, the resulting methanolic crude extracts of A. oliverianum leaves were fractionated to yield soluble fractions of hexane, EtOAc, BuOH, and water. Of these, the EtOAc fraction had the best antioxidant activity. Furthermore, 8 specific phytochemicals were isolated and identified from the EtOAc fraction. Among them, 1,2,3,4,6-O-penta-galloyl-β-d-glucopyranose had the best free radical scavenging activity. These results demonstrate that methanolic extracts and their derived phytochemicals of A. oliverianum leaves have excellent antioxidant activities and thus they have great potential as sources for natural health products. 1. Introduction Molecular and cellular damage due to reactive oxygen species (ROS) is widely believed to be the major cause of aging, neu- ral disorders, diabetes, atherosclerosis, inflammatory injury, cancer, and cardiovascular disease [1]. Thus, a potential scav- enger of ROS may serve as a possible preventive intervention for free-radical-mediated diseases [2]. Plants are potential sources of natural antioxidants. In the past few years, the antioxidant properties of plants have been extensively stud- ied [3, 4]. Among the various medicinal and culinary plants, some endemic species are of particular interest because they may be used for preparations containing phytochemicals with significant antioxidant activities and health benefits [5]. Therefore, the intake of natural antioxidants from plants has been associated with low incidence of cancer, cardiovascular disease, diabetes, and other diseases associated with aging [6]. Taiwan is on the boundary of the tropics and subtrop- ics, and although the island covers only a small area, the environment of Taiwan is diversified, possessing unique indigenous tree species in this island. However, to the best of our knowledge there is no prior report on antioxidative phytochemicals of leaf extracts of indigenous tree species in Taiwan. Thus, in this study, a number of in vitro assays were performed to evaluate the antioxidant activities of methano- lic extracts from the leaves of 18 indigenous tree species. In addition, the characteristics of bioactive phytochemicals were also addressed in this study. 2. Materials and Methods 2.1. Extraction and Fractionation of 18 Indigenous Tree Species. The leaves of 18 indigenous tree species in Taiwan were collected at the end of May 2009 from the Hui-Sun Forest Station of National Chung Hsing University (NCHU) in Nantou County. All voucher specimens including Acacia confusa Merr. (Lu 0069), Acer oliverianum Pax. var. nakaharai (Peng 0001), Calocedrus formosana Florin (Tsai et al. S.N.),