Content of biologically active compounds in Bulgarian propolis: a basis for its standardization

In Bulgaria, propolis tincture is among of the most popular home-made remedies. Bulgarian propolis has been studied and it was found to originate from the bud resin of the black poplar Populus nigra L.; the chemical constituents responsible for its biological activity are flavonoid aglycones (flavones, flavonols, flavanones, dihydroflavonols), substituted cinnamic acids and their esters. However, the specific quantitative characteristics of Bulgarian poplar propolis have not been studied. Validated spectrophotometric procedures were used to quantify the three main groups of bioactive substances: total phenolics, total flavones/flavonols, total flavanones/dihydroflavonols, in 22 samples of Bulgarian propolis from different regions of the country. Based on the results, we characterized raw poplar propolis in terms of minimum content of its bioactive components (antimicrobial and antioxidant) as follows: 46% resin, 24% total phenolics, 7% total flavones/flavonols; 5.4% total flavanones/dihydroflavonols. These values can be used as a basis for Bulgarian propolis standard. They are somewhat higher that the ones suggested by the International Honey Commission for poplar type propolis. This is a proof that Bulgarian propolis is a valuable bee product of high quality, higher than that of the average poplar propolis samples coming from other regions.