Quality of Propolis Commercially Available on Podkarpacki Beekeeping Market

Eight samples of propolis commercially available on south-eastern Poland’s beekeeping market were compared in terms of quality, chemical composition and biological activity, including antioxidant and antimicrobial properties. The organoleptic characteristics and physicochemical requirements indicated that only 50% of tested propolis samples was classified to class II regarding obligatory limits, while the others were out-class. A big variation in mineral composition was determined by the ICP-OES method but all samples were free of heavy metals (Pb, Cd and Ni). Although mesophilic bacteria, yeasts and moulds occurred in tested propolis (in general lower than 10² CFU/g), E. coli and spore-forming sulphite-reducing bacteria as well as Salmonella and Shigella bacteria were not detected. High antioxidant activity and total phenolic content for all samples was confirmed, which was correlated with antibacterial activity tested against E. coli ATCC 11775 strain. Additionally, the propolis sample with the strongest antibacterial activity (MIC 0.33 mg/mL) inhibited biofilm formation of S. aureus and S. epidermidis ATCC 35984 (MBIC 0.66 and 5.25 mg/mL, respectively). However, great variation in terms of antioxidant activity and HPLC polyphenolic profile were observed, and sakuranetin and pinobanksin were identified as the most effective antioxidant components. Moreover, the usefulness of ATR-FTIR spectra analysis was confirmed as a quick method for initial testing of propolis quality.