Phenolic compounds are a group of plant secondary metabolites important in human diet. Together with vitamins they form antioxidant complex productive in eliminating of free radicals. Antioxidant activity of phenolic compounds is closely connected with chemical structure of their. Generally, the antioxidant potential of compound arise from free –OH groups and their substitution in the compound. The main phenolic compounds of pepper fruits are esters of ferulic and sinapic acids and flavonoid glycosides, mainly quercetin, luteolin and apigenin.
The aim of presented work was to determine the relation between phenolic acids and flavonoid derivatives contents in extracts from two parts of pepper fruit: placenta and pericarp in two maturity stages of fruits and their antioxidant activity.
Investigations were made with two sweet pepper cultivars: Red Knight and King Artur. Pericarps and placenta were separated from fresh green and red fruits. The phenolic compounds fraction was isolated from 80% ethanolic homogenate on Sep-Pak C18 cartriges. Extracts were analyzed according to antioxidant activity in DPPH model system and phenolic compounds content by HPLC method. The standards for determination of phenolic compounds were prepared from the pure compounds obtained in our earlier work. The correlation coefficient was evaluated to determine the dependence between phenolic compounds content and antioxidant activity of the extracts.
Analyzed cultivars differed in phenolic compounds content. Higher level of phenolic acid derivatives was found in King A., while in Red K. higher amounts of quercetin, luteolin and apigenin derivatives were calculated. Phenolic acids esters concentration was the highest in red placenta, and it was above ten times higher, than in pericarps. Similar tendence was observed in the extracts from green fruits, where extracts from placenta had almost ten times higher level of phenolic acids derivatives. On the other side derivatives of flavonoids were identified only in pericarp and their concentration was higher in green, than in red fruits. Antioxidant activity investigations showed higher activity of the extracts obtained from red fruits. Additionally these extracts showed comparable activity as well from placenta, as from pericarp. Evaluation of correlation coefficient between phenolic compounds content and antioxidant activity of the fractions showed high dependence between phenolic compounds and antioxidant activity of the extracts from placenta (0,97), while in the fractions from pericarp there were any correlations. On the other side a middle correlation (0,54) between antioxidant activity and phenolic compounds content in red fruits (placenta and pericarp) was found.
It may be concluded, that phenolic acids derivatives, decide about antioxidant potential of the extracts from placenta. In extracts from pericarp other unidentified compounds may be present, which influenced on antioxidant activity of mentioned fraction.

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