天然耐久木材抗腐朽機制之探討

Abstract

為延長木材使用年限，通常會使用防腐劑，然而傳統防腐劑對環境及人體具有高度毒性，若能利用天然產物不僅可降低毒性還能減緩對環境的衝擊。有鑑於此，本研究以本土天然耐腐朽樹種－相思樹（Acacia confusa Merr.）及臺灣杉（Taiwania cryptomerioides Hay.）為研究對象，除了找尋傳統殺菌成分，並篩選具有抗氧化及金屬螯合之成分，以探討對木材耐腐朽性之影響。 以木塊耐腐朽法評估相思樹與臺灣杉天然耐腐性之試驗結果得知，相思樹及臺灣杉心材抽出物對Lenzites betulina白腐菌或Laetiporus sulphureus褐腐菌皆具有良好的耐腐朽能力；而兩者邊材抽出物則不具耐腐朽能力。 進一步評估兩者心材乙醇抽出物及各可溶部之抗腐朽菌及抗氧化能力，由固態平板試驗結果得知，相思樹乙醇抽出物及其3個可溶部之抗腐朽菌能力不佳；而臺灣杉乙醇抽出物具良好抗腐朽菌之活性，且4個可溶部中以正己烷可溶部之抗腐朽菌能力最佳，進一步分離正己烷可溶部，共分離出6個化合物，分別為Ferruginol、Cedrol、T-Cadinol、T-Muurolol、α-Cadinol及Hinokinin。在抗氧化能力方面，臺灣杉乙醇抽出物及其4個可溶部抗氧化能力不佳；相思樹乙醇抽出物具良好抗氧化活性，且3個可溶部中以乙酸乙酯可溶部具有極佳之抗氧化能力，進一步分離乙酸乙酯可溶部，共得5個化合物，分別為Protocatechuic acid、7,8,3’,4’-Tetrahydroxyflavanone、Melanoxetin、Transilitin及Okanin。 將相思樹及臺灣杉各可溶部含浸至柳杉（Cryptomeria japonica D. Don）與楓木（Acer serrulatum Hay.）邊材中，經12週木塊耐腐朽試驗得知，含浸相思樹3個可溶部之柳杉邊材對L. s.皆具有耐腐朽活性，而含浸臺灣杉正己烷可溶部之柳杉具最佳耐腐朽活性；然而無論相思樹或臺灣杉之抽出物含浸於楓木邊材對L. b.皆不具耐腐朽活性。 相思樹之天然耐腐朽活性與本身抽出物相關，雖然其抽出物並無抑菌效果，卻具有良好的抗氧化活性，所以得知相思樹具抗氧化活性之抽出物能夠提升木材對L. s.之耐腐朽能力。因此相思樹抑制腐朽菌腐朽之主要原因來自於抗氧化之抽出物。 臺灣杉天然耐腐朽活性與正己烷可溶部中活性成分有相當大之關連性，且主要是屬於抑菌效果，與其抗氧化能力較無相關性。所以得知臺灣杉天然耐腐朽機制來自於活性成分之殺菌成分，故木材不易受腐朽菌分解。

To extend the wood service life, it is usually treated with preservatives. However, the traditional wood preservatives are highly toxic to environment and human beings. Using natural products as preservatives not only reduces toxicity but also slows down the impact on the environment. In this study the endemic durable species - Acacia confusa Merr. and Taiwania cryptomerioides Hay. were chosen to be investigated. Besides determining compounds with fungicidal activity, antioxidant activities and metal chelating capacity were carried out to explore the influences of active components on natural durable wood. The results showed extracts of A. confusa and T. cryptomerioides heartwood possessed excellent durability against white-rot fungus Lenzites betulina and brown-rot fungus Laetiporus sulphureus after 12 weeks decay resistance test while sapwood extracts didn’t exhibit any decay resistance ability. Antifungal and antioxidant activities of heartwood ethanolic extracts and their fractions were also carried out. The results obtained from agar plate method showed that A. confusa ethanolic extract and its three fractions exhibited no antifungal activity, whereas T. cryptomerioides heartwood ethanolic extracts had good antifungal activity and its n-hexane soluble fraction displayed the best antifungal activity among the four fractions. Six compounds were isolated using bioassay-guided fractionation from the n-hexane soluble fraction and their structures were identified, namely ferruginol, cedrol, T-cadinol, T-muurolol, α-cadinol, and hinokinin. In the antioxidant activity test, however, no significant antioxidant activity was observed with ethanolic extracts and its fractions of T. cryptomerioides heartwood. But ethanolic extracts from A. confusa heartwood had good antioxidant activity and its ethyl acetate soluble fraction showed excellent performance. Five compounds were isolated using bioassay-guided fractionation from the ethyl acetate soluble fraction and their structures were identified, namely protocatechuic acid, 7,8,3’,4’-tetrahydroxyflavanone, melanoxetin, transilitin, and okanin. In addition, fractions of heartwood extracts from A. confusa and T. cryptomerioides were soaked in sapwoods of Cryptomeria japonica D. Don and Acer serrulatum Hay. for 12 weeks decay resistance test. Three fractions of A. confusa extract performed good durability against L. s., and n-hexane soluble fraction of T. cryptomerioides extract was superior to other fractions. Sapwoods of A. serrulatum soaked with fractions of two extracts showed no significant resistance to L. b.. Natural durability of A. confusa should be associated with its crude extract. However, the extract from A. confusa didn’t show toxic effectiveness but had good antioxidant activity, which lead to the increase in decay resistance to L. s.. Therefore, the natural durability of A. confusa may be attributable to its antioxidant action. Natural durability of T. cryptomerioides is significantly associated with its active ingredients in the n-hexane soluble fraction whose main action is antifungal rather than antioxidant activity. Therefore, the naturally durable mechanism of T. cryptomerioides is attributable to the active compounds which act as fungicides to prevent deterioration caused by wood rot fungi.