Balsam poplar and black poplar (Populus balsamifera L. and Populus nigra L.) buds that grow in Lithuania are the primary source of propolis, therefore it is proper to evaluate and compare the composition of these raw plant materials and propolis quantitatively and qualitatively. Propolis and balsamic poplar bud extract are dominated by p-coumaric acid and black poplar-caffeic acid. Antioxidant activity was evaluated by DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), FRAP (ferric-reducing antioxidant power) and CUPRAC (cupric reducing antioxidant capacity) methods and all extracts showed antioxidant activity, and obtained results correlated with the obtained amounts of phenolic compounds and flavonoids in the extracts. Studies of antimicrobial activity have shown that all extracts have a growth inhibitory effect against Staphylococcus aureus and Candida albicans, but the extract of balsam poplar buds showed the most significant effect of such kind. Considering the results of the research, it can be stated that balsam poplar buds cultured in Lithuania are the primary raw material of propolis, which is rich in phenolic compounds with antioxidant properties and is a promising raw material for pharmaceutical purposes.

Antioxidant and free radical scavenging effects are attributed to phenolic compounds present in propolis, and when delivered to the skin surface and following penetration into epidermis and dermis, they can contribute to skin protection from damaging action of free radicals that are formed under UV and premature skin aging. This study was designed to determine the penetration of phenolic acids and vanillin into the human skinin vitrofrom experimentally designed vehicles. Results of the study demonstrated the ability of propolis phenolic acids (vanillic, coumaric, caffeic, and ferulic acids) and vanillin to penetrate into skin epidermis and dermis. The rate of penetration and distribution is affected both by physicochemical characteristics of active substances and physical structure and chemical composition of semisolid vehicle. Vanillin and vanillic acid demonstrated relatively high penetration through epidermis into dermis where these compounds were concentrated, coumaric and ferulic acids were uniformly distributed between epidermis and dermis, and caffeic acid slowly penetrated into epidermis and was not determined in dermis. Further studies are deemed relevant for the development of semisolid topically applied systems designed for efficient delivery of propolis antioxidants into the skin.

The manufacture of ethanol-free propolis solutions offers a broader application. A few trials with Lithuanian propolis have been conducted. The aims of the study are to manufacture propolis water and water-free solutions and evaluate the quality and antimicrobial activity of these solutions. The studied solutions containing 2.5%, 5%, and 10% propolis are prepared. As solvents, purified water, 70% v/v ethanol, 96.3% v/v ethanol, propylene glycol, and their systems were used. Determination of total levels of phenolic compounds (FAE mg/g) is based on colour oxidation-reduction reaction using Folin-Ciocalteu reagent under alkaline conditions and performed at 765 nm wavelength using UV spectrophotometer. The highest content of phenolic compounds was determined in solutions containing 10% propolis extracts, and the lowest amounts in 2.5% propolis extracts. The water extracted the lowest amount of phenolic compounds from crude propolis, ethanol extracted the highest amount, and propylene glycol ranked the middle position. It is determined that technological parameters (stirring, temperature) contribute to content of phenolic compounds. During microbiological study, MICs were determined. The studies showed that water extracted propolis solutions and solvents mixture did not inhibit the growth of the studied microorganisms, and propolis solutions in propylene glycol were found to have antimicrobial activity.

Phenolic compounds with miscellaneous biological activities are an interesting component in dermatology and cosmetology practices. The aim of our study was to determine the phenolic compounds released from emulsion, emulgel, gel, ointment, and oleogel formulations penetration into human skin layers, both the epidermis and dermis, and estimate their antioxidant activity. The ex vivo penetration study was performed using Bronaugh type flow-through diffusion cells. Penetration studies revealed that, within 24 h, the chlorogenic acid released from the oleogel penetrated into skin layers to a depth of 2.0 ± 0.1 µg/mL in the epidermis and 1.5 ± 0.07 µg/mL in the dermis. The oleogel-released complex of phenolic compounds penetrating into epidermis showed the strongest DPPH free radical scavenging activity (281.8 ± 14.1 µM TE/L). The study estimated a strong positive correlation (r = 0.729) between the amount of quercetin penetrated into epidermis and the antioxidant activity detected in the epidermis extract. Plant based phenolic compounds demonstrated antioxidant activity and showed great permeability properties through the skin.

The balsam poplar (Populus balsamifera L.) buds that grow in Lithuania are a polyphenol-rich plant material with a chemical composition close to that of propolis. In order to potentially adapt the extracts of this plant’s raw material for therapeutic purposes, it is important to carry out detailed studies on the chemical composition and biological activity of balsam poplar buds. An important step is to evaluate the yield of polyphenols by different extraction methods and using different solvents. According to our research, extracts of balsam poplar buds collected in Lithuania are dominated by p-coumaric (496.9–13,291.2 µg/g), cinnamic acid (32.9–11,788.5 µg/g), pinobanksin (34.9–1775.5 µg/g) and salicin (215.3–1190.7 µg/g). The antioxidant activity of poplar buds was evaluated by the ABTS (2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), DPPH (2,2-diphenyl-1-picrylhydrazyl) and FRAP (ferric-reducing antioxidant power) methods, all extracts showed antioxidant activity and the obtained results correlated with the obtained amounts of total phenolic compounds in the extracts (ABTS r = 0.974; DPPH r = 0.986; FRAP r = 0.955, p < 0.01). Studies of antimicrobial activity have shown that ethanolic extracts have an antimicrobal activity effect against Staphylococcus aureus, Enterococcus faecalis and Escherichia coli. The extracts showed a better antimicrobal activity against gram-positive bacteria.