ABSTRACT 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.

Presence of fungi in food and feed products is a major problem. Fungi synthesize a large number of secondary metabolites including particularly harmful mycotoxins. They can be produced in plant tissues and are commonly found all over the world in many products including cereals. A total of 44 samples were taken for identification of ergosterol - the potential marker of fungal presence. Fourteen of these samples were chosen for further studies that included the evaluation of the relationship between ergosterol content and three major mycotoxins produced by Fusariumspp.: fumonisin B1, zearalenone and deoxynivalenol. Fungal strains were also isolated and identified by molecular means in those samples. The results of the studies give a further and more detailed insight into the relationship between contents of ergosterol and mycotoxins in different cereal products. It was found that there was no correlation between content of ergosterol and mycotoxins in the tested food products. Also, the presence of mycotoxins was not correlated with occurrence of species able to produce these toxins.