Characterization of secondary metabolites in Drimia maritima (L.) Stearn and Strophanthus kombé Oliv. as well as fermented extracts derived therefrom by liquid chromatography-diode array/mass spectrometric detection

Mediterranean sea squill (Drimia maritima (L.) Stearn) and African Strophanthus kombé Oliv. seeds are used in complementary medicine for the preparation of medicinal product applied for the treatment of heart diseases because of their active compounds, i. e. cardiac glycosides. A procedure for the preparation of extracts derived from these two plant species comprising a fermentation step is specified in the German Homoeopathic Pharmacopoeia (GHP). However, little is known about the secondary metabolite profile of such extracts and the fate of these components upon processing and storage. The present work revealed the characterization of raw materials and fermented extracts by using novel HPLC-DAD-MSn methods without previous sample cleanup. More than 40 bufadienolides and phenolic compounds were tentatively assigned in Drimia maritima, and characteristic compounds were specific to individual plant parts or vegetation stages. Strophanthus kombé seeds revealed the presence of more than 20 cardenolides, including compounds not reported in the literature so far. Differences in the cardenolide contents of seeds of different origins, i. e. Zimbabwe and Malawi, were observed. The metabolization pathways of bufadienolides in D. maritima and cardenolides in S. kombé were described during fermentation. Total cardiac glycoside contents decreased by about 50% within 12 months of storage. Glycosides were gradually converted into their corresponding aglycones, which was attributed to microbial and plant enzyme activities and by acid hydrolysis as a result of lactic acid accumulation.