Pressurized water extraction of naphtodianthrones in St. John's wort (Hypericum perforatum L.)

Abstract

A high pressure water extraction (PWE) method was developed for separation of naphtodianthrones (hypericin, protohypericin, pseudohypericin, and protopseudohypericin) in St. John's wort. The effects of extraction temperature, pressure, pH, particle size, and modifier were studied, and the PWE method was compared to a conventional solvent extraction method. The most important factors affecting the extraction efficiency were found to be temperature, pH and particle size. The highest extraction efficiency of naphtodianthrones was achieved when the extraction was performed using a fine sample powder (≤80 mesh), a low temperature (ambient), and 100 bar pressure at pH ≥ 7. Using these conditions the PWE efficiency to extract naphtodianthrones (the summed amount of hypericin, pseudohypericin and their protoforms) compared to methanol extraction (with ultrasound) was about 80% (90% pseudohypericin and 60% hypericin). PWE extraction efficiency was further improved when ethanol was added to the sample as a modifier before the extraction. Using ethanol modified PWE at pH 7 the summed amount of naphtodianthrones was 90% (95% pseudohypericin and over 80% hypericin ) compared to the methanol extraction with ultrasound. Reproducibility of the optimized PWE method was comparatively good; the relative standard deviation of both hypericin and pseudohypericin was 8%.