抗氧化及抑制黃嘌呤氧化酶成分在相思樹木材之縱徑向分布

相思樹（Acacia confusa）為臺灣本土樹種，其心材、樹皮、葉子、枝條、花及花苞已被證實具有良好之抗氧化活性。為了解相思樹縱向及徑向之活性成分分布及生物活性差異，本研究將單株相思樹由樹幹基部至樹頂依高度分為4區段，而各區段再由髓心往邊材以每7個年輪數分為5個區塊，以乙醇萃取其抽出物，並分別測定總酚類含量和總黃酮類含量，再評估清除DPPH自由基、清除超氧自由基、總抗氧化能力及抑制黃嘌呤氧化酶之生物活性。試驗結果顯示，靠近基部心材之總酚類含量最高，其值介於43.4－44.8 mg GAE/g of wood，縱向之含量以樹木中段心材最多；而總黃酮類含量由邊材往髓心遞增，縱向之含量以樹木中段心材最多。心材各區塊清除DPPH及超氧自由基之評估結果，顯示不論縱向或徑向皆無顯著差異；基部之內層心材抑制黄嘌呤氧化酶之活性最佳，上述3種活性皆與總酚類及總黃酮類含量成正相關，其中又以抑制黄嘌呤氧化酶之活性與總黃酮類含量具有高度相關性。總抗氧化能力之徑向分布皆以邊材為佳，並呈現向髓心遞減趨勢，顯示邊材水溶性總抗氧化能力較佳。進一步定量相思樹心材之4個活性成分：Melacacidin、4’-O-Methyl-melacacidin、Transilitin及Okanin；由定量結果得知Melacacidin和4’-O-Methyl-melacacidin為主要抽出成分。相思樹心材清除DPPH、超氧自由基及抑制黄嘌呤氧化酶之活性與上述4種化合物含量皆呈正相關，其中，又以清除DPPH自由基與Melacacidin和4’-O-Methyl-melacacidin具有高度相關性；而抑制黄嘌呤氧化酶之活性則與Transilitin和Okanin具有高度相關性，由此可知不同活性源自於不同化合物；且清除DPPH、超氧自由基及抑制黄嘌呤氧化酶之活性亦與4種化合物總量呈高度相關性。另外，相思樹活性成分定量結果得知，相較於邊材，4種黃酮類含量於移形材處大量產生，並由移形材向心材內累積。

關鍵字

相思樹；抗氧化活性；縱向分布；徑向分布；移行材；黃嘌呤氧化酶

並列摘要

Acacia confusa Merr. is an indigenous tree species that grows in Taiwan. It has been proven that their extractives of heartwood, bark, leaves, branch, flower and bud exhibited excellent antioxidant activities. The objectives of this study are to understand the difference of bioactivities between radial and longitudinal wood, and to analyze the distribution of bioactive constituents in A. confusa. Four sections were taken based on four different heights from the base to the top of trunk. Each section was divided into five blocks by every seven tree rings from pith to sapwood. All samples were extracted with ethanol, and their bioactivities were evaluated by DPPH radical scavenging (DPPH), superoxide radical scavenging assays (NBT), trolox equivalent antioxidant capacity (TEAC) assay and xanthine oxidase (XOD) inhibitory activity. In addition, total phenolic contents (TPC) and total flavonoids contents (TFC) were also examined. The results from TPC measurement showed that the TPC of heartwood at the tree base had the highest values (43.4－44.8 mg GAE/g of wood), and longitudinal distribution of TPC were higher in the middle trunk. Radial distribution of TFC gradually increased from sapwood toward pith, and longitudinal distribution of TFC were was higher in the middle trunk. Blocks of heartwood showed no significantly statistical difference on DPPH and NBT regardless of radial or longitudinal direction. Inner heartwood at the tree base possessed the best XOD inhibitory activity. The three above-mentioned activities have positive correlation with TPC and TFC, especially, XOD inhibitory activity has a high positive correlation with TPC and TFC. TEAC represents the inhibitory capability of water-soluble free radicals. TEAC was higher in sapwood, and radial distribution of TEAC decreased from the sapwood toward the pith of tree, revaling that extractives of sapwood had better water-soluble antioxidant activity. Furthermore, four main bioactive constituents, melacacidin, 4’-O-methyl-melacacidin, transilitin and okanin, of heartwood extract were quantified using HPLC. Results showed that melacacidin and 4'-O-methyl-melacacidin were two major compounds of the ethanolic extract. Based on statistical analyses, each content of four compounds showed positive correlation with DPPH, NBT and XOD inhibitory activity. Melacacidin and 4’-O-methyl-melacacidin has a high positive correlation with DPPH, transilitin and okanin has a high positive correlation with XOD inhibitory activity, especially. In addition, the total contents of four compounds showed strongly positive correlation with DPPH, NBT and XOD inhibitory activity. Besides, quantitative results obtained in this study showed that four main bioactive constituents were higher in TZ than in sapwood, then gradual accumulation to the other parts of heartwood.