Phenolic compounds as marker compounds for botanical origin determination of German propolis samples based on TLC and TLC-MS

Propolis, a complex mixture of different plant exudates collected and processed by honeybees, contains a wide range of bioactive substances. German propolis has so far only rarely been studied with respect to its constituents and botanical origin. To investigate the composition of specific phenolic constituents in bud extracts and German propolis, TLC and TLC-MS methods were developed. Ethanolic extracts from representative propolis samples and tree buds were analyzed by TLC. Compound assignment was achieved through mass spectrometric detection, and TLC using the DPPH assay was used to assess the antioxidant capacity. According to their TLC fingerprints, propolis samples were classified into three types (O/B/G) based on the results of former investigations. Identification of flavonoid aglycones and their methyl esters as well as acetates or butyrates was possible in both bud exudates of black poplar hybrids (Populus x canadensis Moench 'Robusta') and O-type propolis with TLC-MS. In aspen (Populus tremula L.) and B-type propolis, phenolic acid glycerols were detected as common constituents. Based on the marker compounds identified in the present study, black poplar hybrids and aspens were identified as major sources of the investigated propolis samples whereas horse chestnut (Aesculus hippocastanum L.) and birch (Betula pendula Roth) were of minor importance. The O-type propolis displayed superior antioxidant activity, but also contained higher amounts of potential allergens like caffeic acid derivatives than B-type propolis.