Fermented aqueous as well as hydroethanolic extracts of Strophanthus kombé Oliv. seeds were characterized by UHPLC-DAD.
Strophanthus extracts containing cardioactive cardenolides are still applied in European complementary medicine for the treatment of heart diseases. However, the cardenolide profile and the fate of individual compounds during extraction and storage are not well understood. Therefore, the objective of the present study was to characterize the cardenolide compound pattern in extracts of different polarity and their structural changes upon storage in aqueous fermented preparations. For this purpose, individual cardenolides were quantitated by a UHPLC-DAD validated method using an internal standard. Three different extraction protocols were compared: hydroethanolic extraction under reflux with and without previous defatting of the seed material and ultrasonic-assisted extraction at ambient temperature. Reflux extraction of non-defatted seeds showed maximum cardenolide yields. Differences in the cardenolide contents of seeds of the different origins Zimbabwe and Malawi were observed. The cardenolide profile and metabolization of individual compounds upon fermentation and storage of S. kombé seed extracts revealed that predominant cardenolides, mainly strophanthidin glycosides, changed upon storage over 12 months. Cardenolides exhibiting two or three saccharide moieties were degraded presumably by β-glucosidase activities, originating from the plant material or lactobacilli, releasing the corresponding monoglycosides. The latter were further degraded into the corresponding aglycones probably by acid hydrolysis as a result of lactic acid accumulation.