Chemical diversity of propolis and the problem of standardization.

Chemical variability of propolis is discussed with respect to the problem of standardization. Several chemical types of propolis are formulated, based on their plant source. Reliable criteria for chemical standardization of different propolis types are needed but such generally accepted criteria do not yet exist. The chemical profile of "poplar" propolis, typical for the temperate zone, can be characterized by the following parameters: total flavone and flavonol content, total flavanone and dihydroflavonol content, and total phenolics content. These parameters correlate better with the biological activity and are more informative that the quantification of individual components. There is still a lot of work to be done to achieve standardization of other propolis types. Working with standardized material will allow scientists to connect a particular chemical propolis type to a specific type of biological activity and formulate recommendations for mainstream practitioners.