Nüsslein B, Kurzmann M, Bauer R, Kreis W
Lehrstuhl für Pharmazeutische Biologie der Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstrasse 5, D-91058 Erlangen, Germany.
J Nat Prod. 2000 Dec;63(12):1615-8. doi: 10.1021/np0002839.
Cichoric acid (2R,3R-O-dicaffeoyltartaric acid) (1) is highly susceptible to enzymatic degradation during the preparation of Echinacea purpurea products. Degradation of 1 and other caffeic acid derivatives can be inhibited by antioxidants added to the extraction solvent or in buffered protein extracts saturated with nitrogen. Inhibitor studies conducted with protein extracts prepared from dried overground parts of E. purpurea revealed that polyphenol oxidases (PPO) but not peroxidases are responsible for the oxidative degradation of exogenous and endogenous caffeic acid derivatives. With a view to stabilizing aqueous extracts with respect to their content of 1, the effects of ascorbic acid and ethanol were tested. Compound 1 was not stable under conditions where oxidative processes could almost be excluded. It was found that an esterase hydrolyzing the ester bonds between tartaric acid and caffeic acid is still active under PPO inhibitory conditions. Finally, addition of 40% ethanol and 50 mM ascorbic acid to aqueous extracts of "Echinaceae purpureae herba" resulted in a constant amount of cichoric acid over four weeks.
紫锥菊酸（2R,3R - O - 二咖啡酰酒石酸）（1）在紫锥菊产品制备过程中极易受到酶促降解。在提取溶剂中添加抗氧化剂或在充氮饱和的缓冲蛋白提取物中，1及其他咖啡酸衍生物的降解可受到抑制。用紫锥菊干燥地上部分制备的蛋白提取物进行的抑制剂研究表明，多酚氧化酶（PPO）而非过氧化物酶是外源和内源咖啡酸衍生物氧化降解的原因。为了使水提取物中1的含量稳定，测试了抗坏血酸和乙醇的效果。在几乎可以排除氧化过程的条件下，化合物1并不稳定。发现在PPO抑制条件下，一种水解酒石酸和咖啡酸之间酯键的酯酶仍然具有活性。最后，向“紫锥菊草”水提取物中添加40%乙醇和50 mM抗坏血酸，可使紫锥菊酸在四周内保持恒定含量。
