In the present study, the seasonal variability of the in vitro ferric reducing ability of plasma (FRAP), total phenols, and terpene hydrocarbon content in 70% ethanol extracts were evaluated. The samples of crushed (CBs) and non-crushed ripe juniper berries (NCBs) collected at five localities in North-East Slovakia during the years 2012-2014 were compared. The method of preparation of the extract influenced the amount of dry matter (DM) in the extracts. In the CB extracts were statistically higher contents of DM (from 13.91 ± 0.11 g·L-1 to 23.84 ± 0.14 g·L-1) compared to NCB extracts (from 1.39 ± 0.01 g·L-1 to 16.55 ± 0.09 g·L-1). The differences in antioxidant activity between the investigated localities were statistically significant for both types of extract. For example, in 2013 in the locality of Zbojné, the FRAP in NCBs was 76.62 µmol·L-1·g-1 DM and in CBs was 138.27 µmol·L-1·g-1 DM, while in the Miľpoš locality, in NCBs there was 232.66 µmol·L-1·g-1 DM and in CBs there was 1178.98 µmol·L-1·g-1 DM. The differences in the antioxidant activity between the studied years in the case of NCB extracts were not statistically significant. In the case of CB extracts, significant differences between the evaluated years were found. Statistics by ANOVA confirmed that CB extracts prepared from berries in the year 2013 showed significantly higher activity compared to CB extracts from berries from the years 2012 and 2014. Based on the Pearson we found a negative correlation coefficient between the FRAP assay and the content of total polyphenols in NCB extracts (-0.531 in 2012; -0.349 in 2013; and -0.224 in 2014). In contrast, CB extracts showed a positive correlation coefficient (0.843 in 2012; 0.742 in 2013; 0.617 in 2014).
Keywords: FRAP; antioxidant activity; ethanol extracts; terpene hydrocarbons; total phenols.