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The objective of this study was to determine total phenolic and flavonoid contents, antioxidant and antimicrobial activities of methanolic extracts from the leaves and barks of three Alnus species. The phenolic and flavonoid contents of extracts were determined spectrophotometrically using Folin-Ciocalteau and aluminium chloride methods, respectively. In addition, antioxidant activity of the extracts was determined using 1,1-diphenyl-2-picrylhydrazyl radical scavenging method. The antimicrobial activity was performed by disc diffusion assay against six reference bacterial strains including Gram-negative and Gram-positive bacteria and two fungal strains. Extract of Alnus viridis bark contained the highest amounts of total phenolics (780 mg CAT/g), while extract of A. viridis leaves had the highest amount of flavonoids (30.01 mg RUT/g). All extracts showed antioxidant activity higher than thymol, which was used as a positive probe. The largest diameters of inhibition zone (25 mm) were recorded with Bacillus subtilis 168 M and Staphylococcus aureus ATCC 6538.

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The phenolic composition, as well as the antioxidant and antimicrobial activities of two poorly investigated Achillea species, Achillea lingulata Waldst. and the endemic Achillea abrotanoides Vis., were studied. To obtain a more detailed phytochemical profile, four solvents with different polarities were used for the preparation of the plant extracts whose phenolic composition was analyzed using UHPLC-MS/MS (ultra-high performance liquid chromatography-tandem mass spectrometry). The results indicate that both of the investigated Achillea species are very rich in both phenolic acids and flavonoids, but that their profiles differ significantly. Chloroform extracts from both species had the highest yields and were the most chemically versatile. The majority of the examined extracts showed antimicrobial activity, while ethanolic extracts from both species were potent against all tested microorganisms. Furthermore, the antioxidant activity of the extracts was evaluated. It was found that the ethanolic extracts possessed the strongest antioxidant activities, although these extracts did not contain the highest amounts of detected phenolic compounds. In addition, several representatives of phenolic compounds were also assayed for these biological activities. Results suggest that ethanol is a sufficient solvent for the isolation of biologically active compounds from both Achillea species. Moreover, it was shown that the flavonoids naringenin and morin are mainly responsible for these antimicrobial activities, while caffeic, salicylic, chlorogenic, p-coumaric, p-hydroxybenzoic, and rosmarinic acid are responsible for the antioxidant activities of the Achillea extracts.

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