“…According to the literature data, the biological activity of propolis is mainly attributed to the presence of phenolic compounds, especially flavonoids, phenolic acids, and their esters [ 1 , 6 , 10 ]. For this reason, the phenolic fraction is the most extensively investigated among all constituents determined in propolis samples collected from various geographical regions [ 3 , 9 , 12 , 14 ]. Phenolic compounds regularly determined in poplar-type propolis samples include pinocembrin, galangin, chrysin, kaempferol, catechin, quercetin, rutin, pinostrobin, pinobanksin, naringenin, caffeic acid, coumaric acid, ferulic acid, caffeic acid phenethyl ester, or caffeic acid cinnamyl ester [ 11 , 14 , 15 , 16 , 17 , 18 ].…”