Seasonal changes in phenolic compounds and in the biological activities of Baccharis dentata (Vell.) G.M. Barroso

Baccharis, a large genus of Asteraceae, has been extensively studied because of the medicinal properties of its species. The present study determined the seasonal variation of the levels of total phenolic compounds and flavonoids of Baccharis dentata, and determined the antioxidant and bactericidal potential of the plant extracts. Aerial parts of B. dentata were harvested during the seasons of 1 year. Samples of 0.1 g dry mass (DM) were extracted with aqueous methanol (80%; v/v), and used for quantification of phenolic compounds, quercetin-derived flavonoids and antioxidant activity (DPPH). Caffeic acid and the flavonoids rutin, quercetin, apigenin and kaempferol were quantified in methanolic extracts (0.5 g DM) by HPLC. The micro-dilution method was applied for the determination of the minimal inhibitory concentration (MIC) of selected bacteria strains. Concentrations of total phenolic compounds and flavonoids showed significant seasonal variation, and the antioxidant potential of extracts was related to the concentration of these compounds. Highest antioxidant activity was detected in the extracts from summer and winter plants. Concentrations of quercetin, kaempferol and apigenin were markedly higher in spring and summer plants when compared to the other seasons. This result may be related to the antibacterial activity of n-butanolic and aqueous fractions against Staphylococcus aureus. This is the first report on seasonal changes of secondary compounds and biological activities on B. dentata and might be useful to prospection of novel molecules with antioxidant and antimicrobial properties.