Chalcones in Bioactive Argentine Propolis Collected in Arid Environments

The aim of this study was to assess the chemical and biological profile of propolis samples collected in arid environments of north-western Argentina. The samples were from two phytogeographical regions (Prepuna and Monte de Catamarca Province). Propolis ethanolic extracts (PEE) and chloroform (CHL), hexane (HEX) and aqueous (AQ) sub-extracts of samples from three regions (CAT-I; CAT-II and CAT-III) were obtained. All PEE exhibited antioxidant activity in the DPPH radical scavenging assay (SC50 values between 28 and 43 μg DW/mL). The CHL extract was the most active (SC50 values between 10 and 37 μg DW/mL). The antioxidant activity in the β-carotene bleaching assays was more effective for PEE and CHL (IC50 values between 2 and 9 μg DW/mL, respectively). A similar pattern was observed for antibacterial activity. The highest inhibitory effect on the growth of human Gram-positive bacteria was observed for CHL-III and CHL-I (Monte region) with minimal inhibitory concentration values (MIC100) of 50 to 100 μg DW/mL. Nine compounds were identified by HPLC-PAD. Two of them (2′,4′-dihydroxychalcone and 2′,4′- dihydroxy 3′-methoxychalcone) were found only in propolis samples from the Monte phytogeographical region. We consider that the Argentine arid region is appropriate to place hives in order to obtain propolis of excellent quality because the dominant life forms in that environment are shrubby species that produce resinous exudates with a high content of chalcones, flavones and flavonols.