Water as extraction solvent for willow bark and artichoke leaves

Pure water is rarely used in extraction technology. However, water extracts will be monographed in Ph Eur for willow bark and artichoke leaves [1,2]. In both cases, some special phytochemical aspects have to be taken into consideration to establish a convenient and reproducible extraction protocol. In willow bark, hydrolysis of the salicin derivatives like salicortin and tremulacin is improved compared to ethanol/water mixtures. Approximately 53% of the total salicin will be detected as salicin after an extraction with demineralised water at 25°C. The rate can be increased up to 70% by adjusting the pH to 7.2 during the process. The hydrolysis of the salicin esters shows a similar kinetic compared to pure salicortin [3]. Chlorogenic acid has been selected as lead compound in Ph Eur monographs of artichoke leaves and extracts [2] by the working group 13B. Hardly any chlorogenic acid will be extracted by using cold water. The situation changes drastically with hot water. The best yield will result at 70–80°C by maceration during one hour. The fingerprint is equivalent to the fingerprint of the herbal drug. At higher temperatures (90°C and boiling water) a reduction of the chlorogenic acid is observed. A further peak elutes just before the chlorogenic acid. This peak is supposed to be an isomerization product of the chlorogenic acid. Furthermore, the fingerprint is changed by an additional peak between chlorogenic acid and flavonoids. It can be concluded that aqueous extracts are a useful and, in some cases, an equivalent complement to ethanolic extracts. Temperature and pH influence thereby the spectrum of the extracted substances.

Acknowledgments: We thank SWISSMEDIC, Department of Pharmacopoeia, for the financial support.

References: [1] EDQM (2006) Draft monograph, Willow bark dry extract. Pharmeuropa 18.1, 158–159. [2] EDQM (2007) Draft monograph, Artichoke leaf dry extract. Pharmeuropa 19.1, 56–57. [3] Meier B. (1988) Salicylate in einheimischen Arzneipflanzen, Schweizer Apotheker-Zeitung 126, 725–733.