Phytochemical Profile, Plant Precursors and Some Properties of Georgian Propolis

Propolis (bee glue) is a resinous substance produced by different species of bees i.a. from available plant resins, balsams, and exudates. It is characterized by significant biological activity (e.g., antimicrobial and antioxidant) and phytochemical diversity related to the available plant sources in specific geographical regions. The available scientific literature on propolis is quite extensive; however, there are only a few reports about propolis originating from Georgia. Therefore, our research was focused on the characterization of Georgian propolis in terms of phytochemical composition and antimicrobial/antioxidant activity. Performed research included UHPLC-DAD-MS/MS phytochemical profiling, determination of total phenolic and flavonoid content, antiradical and antioxidant activity (DPPH and FRAP assays) as well as antibacterial activity of propolis extracts obtained using 70% ethanol (70EE). Georgian propolis extracts exhibited strong activity against Gram-positive bacteria (22 mm-disc assay/64 µg/mL-MIC for S. aureus, sample from Imereti) and weaker against Gram-negative strains as well as strong antioxidant properties (up to 117.71 ± 1.04 mgGAE/g in DPPH assay, up to 16.83 ± 1.02 mmol Fe²⁺/g in FRAP assay for samples from Orgora and Qvakhreli, respectively). The phytochemical profile of Georgian propolis was characterized by the presence of flavonoids, free phenolic acids, and their esters. In most of the samples, flavonoids were the main chemical group (52 compounds), represented mainly by 3-O-pinobanksin acetate, pinocembrin, chrysin, galangin, and pinobanksin. The primary plant precursor of the Georgian bee glue is black poplar (Populus nigra L.) while the secondary is aspen poplar (P. tremula L.).