The role of seasonality on the chemical composition, antioxidant activity and cytotoxicity of Polish propolis in human erythrocytes

Propolis extracts possess beneficial biological effects, such as antioxidant activity. However, the composition of propolis and biological properties of its extracts depend on many factor, including time of harvesting. The main purpose of this study was to evaluate the seasonal effect on the phenolic profile of Polish propolis extracts and their antioxidant activity. Propolis samples were collected from the same apiary during three seasons of the year. The chemical composition (contents of phenolic acids and flavonoids) of ethanolic propolis extracts was determined by ultra-performance liquid chromatography equipped with a photodiode detector and a triple quadrupole mass spectrometer. The antioxidant potential of propolis extracts was evaluated. Additionally, in vitro effects of propolis extracts on the morphology of human red blood cells and the selective permeability of their membrane were determined. The capacity of propolis extracts to protect human red blood cells against free radical-induced hemolysis was also studied. The analyze of the chemical composition of propolis extracts collected in three season of the year indicated that the sum of determined flavonoids and phenolic acids was the highest in the sample harvested in the spring (125.14 mg/g) and it was the lowest in the extract of material collected in the fall (110.09 mg/g), but the differences were slightly. The concentration of examined phenols in propolis samples collected in different seasons was similar and only content of seven among fifteen determined compound was significantly different in extracts according to statistical analysis. The propolis extracts possess high antioxidant potential and significantly protect human red blood cells from oxidative damage. There was no significant differences with regard to the seasonal effect on the chemical profile and antioxidant potential of Polish propolis extracts. These results indicate that the time of Polish propolis harvesting have no influence on phenolic profile and antioxidant activity of its extract.