Comprehensive phytochemical characterization of St. John's wort (Hypericum perforatum L.) oil macerates obtained by...

The aim of the present study was to investigate the impact of crucial process parameters, i.e. of light and temperature conditions, during the preparation of St. John's wort (SJW, Hypericum perforatum L.) Arachis oil macerates. Extracts were prepared according to a standardized protocol over a period of 28 days. For this purpose, flowering tops of H. perforatum were macerated with Arachis oil (drug extract ratio, DERnative 1:4) under different light and temperature conditions. Spectrophotometric measurements were carried out to quantitate naphthodianthrones and to characterize extract color in the CIE L*C*h° system. Moreover, individual plant secondary metabolites were screened by UHPLC-DAD-MSn measurements following liquid-liquid extraction of the oil macerates with methanol. For quantitation purposes, the chromatographic method was validated using reference standards. This methodology allowed the separation of up to 25 constituents in oily and methanolic SJW extracts, covering hydroxycinnamic acids, flavanols, proanthocyanidins, flavonol glycosides, flavonol aglyca, biflavones, bisanthraquinone glycosides, naphthodianthrones and phloroglucinols. Lowest naphthodianthrone contents were determined in oil macerates recovered at 5 °C, whereas highest amounts were detected upon extraction at 50 °C (both under the exclusion of light). Color shades of the oil macerates differed markedly, revealing e. g. a*-values ranging from -4.6±0.3 to 42.5±0.3. The flavonoids quercetin, kaempferol and I3, II8-biapigenin as well as the phloroglucinols hyperforin and adhyperforin could be simultaneously detected and quantitated in all oil macerates. Contents of these constituents varied noticeably between macerates prepared under different conditions (quercetin 14.7±1.2 to 21.8±0.6 μg/g, kaempferol 3.0±0.1 to 5.4±0.4 μg/g, I3, II8-biapigenin 4.4±0.2 to 7.4±0.4 μg/g, hyperforin 52.6±46.0 to 451.4±24.9 μg/g, adhyperforin 6.9±5.7 to 74.5±7.1 μg/g). These results confirm that the quality of the resulting plant extracts is largely determined by the respective process parameters, i.e. especially temperature and light conditions, and thus must be thoroughly chosen and monitored to obtain tailor-made preparations.