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標題: Continuous Hot Pressurized Solvents Extraction of Scavenging DPPH (1,1-diphenyl-2-picryl-hydrazyl) Free Radical Compounds from Taiwan Yams-Dioscorea alata
作者: 陳柏延
Chem, Po-Yen
關鍵字: Dioscorea;山藥;DPPH free radical;continuous hot pressurized solvent;DPPH 自由基;連續式熱壓溶劑
出版社: 化學工程學系
This study preliminarily investigates the scavenging-activity on the DPPH (1,1-diphenyl- 2-picryl-hydrazyl) free radical, individually by the extract of both meat and peel portions of three Taiwan yams “Dioscorea alata”. Liquid-liquid extractions were employed to generate six fractions, initially extracted by ethanol. Then, the aqueous solution of dried solid residues was sequentially fractionated by hexane, chloroform, ethyl acetate, and n-butanol. The EC50 value, defined as the UV absorption of DPPH concentrations sufficiently decrease down to 50% of the original value, was individually detected for six partitions. It was found that all peel portions have better effect on scavenging DPPH free radical than meat portions, especially for the ethyl acetate partition of the peel portion of Tai-nung #2 Yam. Its EC50 value (14.5µg/ml) was even lower than that of ascorbic acid (21.4µg/ml). There is no diosgenin found in three yams, however, there is 0.11 wt% in one yam imported from China. Furthermore, semi-continuous hot pressurized ethanol (HPE) was superior to hot pressurized water (HPW) in extracting the compound scavenging DPPH radical from purpurea Roxb peel. The recovery of four unknown compounds was corresponding to the scavenging ratio of DPPH free radical in the HPE extract. Finally, three-level and four-factor experimental design discovered that ethanol ratio and temperature were the most effective factors in order. Pressure and solvent-to-feed ratio were relatively not significant. 80% of aqueous ethanol, 20 (kg/kg) solid ratio, 180 psig, and 100℃ were found to be a suitable condition.

本研究首先以三種台灣產食用山藥為研究對象。探討皮和肉部分的萃出物對捕捉DPPH自由基的活性。乙醇索氏萃取的乾燥粗水萃液,相繼地再以正己烷、氯仿、乙酸乙酯、正丁醇進行液-液萃取。每一種液-液分層物與DPPH自由基反應後的濃度下降到50%原始吸收值時定義為EC50,其值愈低,代表具高抗氧化性。結果發現,三種山藥皮部份之各分層對於DPPH自由基的清除率,均優於肉的部分。特別是台農二號山藥皮的乙酸乙酯的分離層,呈現14.5µg/ml的EC50值。但是三種山藥均無法檢測出山藥皂素。大陸進口的藥用茅淮山藥卻含有0.11%的山藥皂素。再者,吾人利用半連續式熱壓水與熱壓乙醇分別萃取紫玉血薯山藥皮的抗DPPH自由基成份。熱壓乙醇萃取抗DPPH成分的效率優於熱壓水萃取,且熱壓乙醇萃出液中四未知成份的回收率對應於DPPH的清除率。最後,吾人採取四種變數(乙醇比例、溶固比、壓力、溫度)的L9實驗設計法發現,在80%的乙醇、20 (kg/kg)的溶固比、180psig和100℃的萃出液對於清除DPPH自由基有最好的效果。經由統計分析顯示,乙醇的比例和萃取溫度分別是首要及次要因子。
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