The search for biological activity in Finnish plant extracts containing phenolic compounds

Plants from the Finnish flora were extracted and studied for their biological activity in vitro, especially in relation to phenolic compounds, which are known to have several beneficial health effects. The content of total phenolic compounds in 92 crude plant extracts was determined according to the FolinCiocalteu procedure, and the antioxidant activities of the extracts were measured as inhibition of the autoxidation of methyl linoleate. The respective values showed good correlation, and Andromeda polifolia, Thymus vulgaris, Filipendula ulmaria, Calluna vulgaris, and leaves of Rubus chamaemorus had the best antioxidative activities. The calcium antagonistic activity of 51 extracts was investigated as the inhibition of depolarisation-induced Ca uptake in rat pituitary GH4C1 cells. The most effective plants were Humulus lupulus, Epilobium angustifolium, Lythrum salicaria, and Lysimachia vulgaris. The extracts of Allium cepa, Carum carvi, Malus pumila, and Thymus vulgaris had an adverse effect i.e. promoted fluxes into the cells. These effects did not correlate with the content of total phenolics. Diffusion methods were utilised to screen the antimicrobial effects of 13 phenolic compounds and 29 plant extracts. Among the standards, the widest antimicrobial activity was achieved with flavone, quercetin, morin, and naringenin. In the class of plant extracts, Epilobium angustifolium and Filipendula ulmaria showed the most effective bactericidic effects, whereas the extract of Lythrum salicaria was effective against both Escherichia coli and the yeast, Candida albicans. Antimicrobial effects were also noted for Betula pubescens and Pinus sylvestris, and berries of plants belonging to the genus Rubus. In order to study the chemical basis of the results obtained, the polyphenolic composition of the crude extract of Lythrum salicaria was characterised after fractionation using HPLC/DAD-UV and two HPLC/MS methods. The presence of flavone-C-glucosides was determined by a positive ion LC/APCI-MS method, and a negative ion LC/ESI-MS method was used to identify the tannins and phenolic acids. Based on UV and MS spectral data and reference material, a total of six compounds (vescalagin, pedunculagin, valoneic acid dilactone, 1,6-di-O-galloylglucose, 1-O-galloylglucose and 6-O-galloylglucose) were identified from Lythrum salicaria for the first time. The detection of four flavonoids and six other phenolics confirmed the information presented in the literature. In order to further develop the applicability of LC/MS techniques in phytochemical characterisation, the effect of nine different eluent compositions on the ionisation efficiency of five flavonoids was studied using ionspray (IS), atmospheric pressure chemical ionisation (APCI), and the novel atmospheric pressure photoionisation (APPI). The optimal ionisation conditions were achieved in positive ion IS and APCI using 0.4% formic acid as buffer (pH 2.3), and in negative ion IS and APCI using ammonium acetate buffer adjusted to pH 4.0. For APPI work, the eluent of choice was a mixture of organic solvent and 5 mM aqueous ammonium acetate. The limits of detection (LOD) were determined for the analytes using each interface. Negative ion IS showed the lowest LODs (0.8–13 μM) with an eluent system consisting of acidic ammonium acetate buffer, so this is why this method provides the best conditions for the detection of flavonoids in MS mode.