Antimicrobial potential of different propolis extracts

Introduction: Propolis is a mixture of different types of beeswax and resins collected from plants by bees (Apis mellifera). The role of propolis in the hive is related to its mechanical properties and it is used to construct, adapt and protect the hive; its antimicrobial activity ensures an aseptic environment. Propolis is known for having antibacterial activity conferred by the presence of flavonoids, aromatic acids and esters in their composition and for the presence of ferulic and caffeic acids. Several authors reported that the activity of each chemical compound present in propolis is influenced by the extraction method. These compounds are quite soluble in ethanol, however, the extracts resulting from this solvent can only be used if the ethanol is food grade. Other solvents such as propylene glycol, glycerol and oils, as well as other techniques, have been tested and have shown promising results regarding their composition and biological activities. Discussion & Conclusions: Apparently, the solvent did not affect the pH value of the propolis extracts. Ethanol and PG allowed better extractions of the phenolic compounds presented in propolis, with similar concentration values. The antioxidant activities of all extracts were similar and their composition was identical, varying only in the content of flavonoid compounds. Caffeic acid, coumaric acid, ferulic acid, quercetin and kaempferol were identified by HPLC. Propolis extracted with ethanol and PG showed higher antimicrobial activity against several microorganisms. All propolis extracted with PG, at both temperatures, inhibited most of the microorganisms tested. However, at 50 ºC, 0.3125 μg/ml of propolis extract was enough to inhibit a large number of microorganisms. Propolis 1, extracted with PG at 50 ºC demonstrated quite promising results. As conclusion, although further tests are required, propolis extracted with PG, a compound that according to the United States FDA is Generally Recognized as Safe (GRAS), could be a promising product to be used in food industry to, for example, reduce the microbial loads of raw meats and avoid cross-contaminations.