不同萃取方法及乾燥熱處理對苧麻葉和根的抗氧化能力表現之探討

本研究第一部份擬針對苧麻葉與根探討其抗氧化能力，並以不同萃取方法、不同乾燥處理方式及經遠紅外線照射對其抗氧化能力之影響，研究結果顯示，在不同萃取方法中，新鮮苧麻葉與根皆以95%乙醇萃取物的抗氧化成分(總酚類和類黃酮)及抗氧化能力(清除ABTS(2,2`-azinobis?3-ethylben-zothiazo-line-6- sulfonic acid?和DPPH(α,α-diphenyl-β-picrylhydrazyl)自由基)為最高，其次為熱水萃取物和冷水萃取物，而新鮮苧麻根乙醇萃取物總酚類含量為200.24 ±0.93 mg/g，約高於新鮮苧麻葉乙醇萃取物的4.5倍，其清除ABTS自由基能力是新鮮苧麻葉乙醇萃取物的7.4倍，約為維生素衍生物(Trolox)的1/3倍。經冷凍乾燥和日曬乾燥的苧麻葉熱水萃取物其抗氧化成分較新鮮者低約55至67 %，而對DPPH自由基清除能力其EC50分別為19.05 mg/ml和15.61 mg/ml，相對其抗氧化能力卻較新鮮者為高約40至60%；經日曬乾燥苧麻根熱水萃取物其清除ABTS自由基能力(EC50=34.16 μg/ml)明顯較新鮮者為高，顯示其清除自由基能力只剩1/10。經遠紅外線照射和烘箱熱風處理(110℃, 60 min)的日曬苧麻葉皆可提高熱水的萃取率，但其抗氧化能力表現上則無顯著差異(p＞0.05)；而經遠紅外線照射和烘箱熱風處理的日曬苧麻根其抗氧化能力皆較未處理組高，且達顯著差異(p＜0.05)。第二部分將抗氧化能力較高的萃取物，包括苧麻葉與根的熱水及乙醇萃取物添加於大豆油中，探討其對油脂貯藏安定性之影響及開發加入苧麻葉或根的XO醬產品，並藉由測定油脂中過氧化價(peroxide value，POV)和硫巴比妥酸值(thiobar-bituric acid value，TBA)值評估其油脂氧化程度，結果貯存在70℃下第8天時，添加0.1 %苧麻葉與根乙醇萃取物，其POV值分別為56.27±0.12 meq/kg與57.13±0.50 meq/kg，皆較對照組(53.33 ±0.31 meq/kg)高，顯示以0.1 %的苧麻葉和根萃取物添加大豆油中並不具抑制油脂氧化作用。添加10 %的新鮮苧麻根於XO醬中，在貯存50℃下28天時，其POV值為24.33 ±1.33 meq/kg，較對照組(32.40 ±0.53 meq/kg)低，顯示添加10 %新鮮苧麻根於XO醬中可延緩油脂氧化的速率，但添加10 %新鮮苧麻葉於XO醬中反而促進油脂氧化。

關鍵字

苧麻； HASH(0x8cba070) ； HASH(0x8cba0e8)

並列摘要

The first part of this research was to investigate anti-oxidant abilities of Boehmeria nivea leaf and root. Different extraction methods, drying conditions as well as far infrared were applied to measure their effects on anti-oxidant abilities of Boehmeria nivea leaf and root. Results showed that 95% ethanol extracts of fresh leaves and roots demonstrate the highest anti-oxidant components(total contents of phenol compounds and flavonoids)and scavenging abilities free radical (scavengingABTS(2,2`-azinobis?3-ethylbenzothiazoline-6- sulfonic acid?and DPPH (α,α-diphenyl-β-picrylhydrazyl) free radical ), followed by hot water and cold water extraction. The total contents of phenol compounds of fresh Boehmeria nivea root was 200.24± 0.93 mg/g, which is 4.5 times higher than ethanol extracts of fresh Boehmeria nivea leaf, and its ability to remove ABTS free radical is 7.4 times higher than that of fresh Boehmeria nivea leaf, which is one third of Trolox's ability to remove free radical. Antioxidant components of hot water extracts of Boehmeria nivea leaf exhibited 55 and 67% lower than that of fresh leaf respectively. For the DPPH free radical scavenging, their EC50 values are 19.05 mg/ml and 15.61 mg/ml respectively, but their anti-oxidant capacities are 40 to 60 % higher than fresh ones. Hot water extracts of Boehmeria nivea root experienced sun dry treatment have a better ability to scavenging ABTS free radical (EC50=34.16 μg/ml)when compared to that of fresh root, which only have one tenth anti-oxidant ability left. It was also found that far infrared and oven hot air treatments(110℃, 60 min) both can improve hot water extraction rates of sun dried leaves, but no significant difference was observed in anti-oxidant abilities between them (p>0.05). Sun dried roots with far infrared and oven hot air treatments exhibited higher antioxidant abilities significantly compared to the roots without any treatments (p<0.05). Extracts with higher antioxidant abilities, including hot water and ethanol extracts of Boehmeria nivea leaves and roots, were screened and then added into soy bean oil to study effects on oil stabilities of oxidation during storage and also to develop new XO paste products containing Boehmeria nivea leaves and roots. The extents of oil oxidation in XO paste were evaluated by measuring POV (peroxide value ) and TBA (thiobarbituric acid value ) values. Results indicated that after 8 day storage at 70℃, the POV values of soy bean oil with addition of 0.1% of ethanol extracts of leaf and root were 56.27± 0.12 meq/kg and 57.13± 0.50 meq/kg respectively, which were both greater than that of control samples(53.33 ±0.31 meq/kg), showing that extracts of leaf and root do not have the abilities to inhibit oxidation of soy bean oil. Addition of 10 % fresh Boehmeria nivea root into XO paste for 28 days under 50℃, the POV value was 24.33± 1.33 meq/kg, which is smaller than that of control samples(32.40 ±0.53 meq/kg), indicating an ability to decrease the rate of oil oxidation. However, with the addition of 10% of fresh leaf to XO paste, oil oxidation was promoted instead.