二氧化碳超臨界萃取技術具有較低溫度，高擴散能力之特性，可將天然物中的熱不穩定性物質萃出，並保留活性成分，所以本研究以二氧化碳超臨界流體萃取技術萃取洛神花多酚類物質咖啡酸。洛神花所含有的多酚類物質具有許多的生物活性，其中的有效成分咖啡酸，具備有抗氧化、捕捉自由基、抑制酪氨酸酶的功能。將不同比例的水、乙醇作為共溶劑添加至二氧化碳超臨界流體中進行修飾，並且改變不同的臨界壓力、臨界溫度、與超臨界流體的流速藉此評估使用共溶劑修飾的超臨界流體萃取洛神花咖啡酸效率的最佳化條件。根據高效能液相層析儀針對萃取物的咖啡酸含量分析結果，可以得到的最佳化萃取條件為臨界壓力250 bar、臨界溫度40℃、共溶劑乙醇濃度85%、共溶劑流量1.2 ml/min。在抗氧化活性當中，其氧化還原能力、清除DPPH 自由基及酪氨酸酶之能力測定發現當咖啡酸萃取率上升，清除DPPH 自由基則提升，而氧化還原能力上咖啡酸萃取率也頗佳，但酪氨酸酶能力上，則看不出相同趨勢，但在HPLC 圖譜上較複雜，可能萃取出含有較優異抑制酪氨酸酶之成分。

Supercritical carbon dioxide (SC-CO2) can provide a benefit of lower temperature and highdiffusion ability in nature product extraction process, not only preserved the thermo unstablebut also keep the bioactivity of the extracts. Owing to this, we use supercritical carbondioxide extract the caffeic acid (CA), a kind of polyphenol, from Roselle. Caffeic acid hasabilities with antioxidant, radical catching and tyrosinase inhibition. We add water andalcohol as the co-solvent to modify the polarity of the supercritical carbon dioxide, and usethis modified supercritical carbon dioxide in the caffeic acid extraction with differ criticaltemperatures, critical pressures and flow rates. In the results of the further analysis by highperformance liquid chromatography, the best optimization in modified supercritical carbondioxide extraction of caffeic acid needs critical pressure at 250bar, critical temperature at 40℃, Co-solvent 85% ethanol as co-solvent at the flow rate 1.2ml/min.Among the antioxidant activity of its redox ability to remove DPPH Radicals and the abilityto determine tyrosinase found that caffeic acid extraction rate, clear the DPPH Free radicalsare improving, and redox ability of caffeic acid on the extraction rate is quite good, buttyrosinase Ability, then do not see the same trend, but more complicated on the HPLCchromatogram, may be extracted With excellent inhibition of tyrosinase than the ingredients.