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Two fraction, one containing flavonols, flavan-3-ols, phenolic acids and the other containing anthocyanins, were isolated from Rubus (red raspberry, blackberry) and Prunus (sweet cherry, sour cherry) fruits to study their phenol content by HPLC and antioxidant activity using the DPPH test. Raspberries and blackberries were characterised by catechins and ellagic acid derivatives; sour and sweet cherries by phenolic acids. All fruits had relatively high anthocyanin content. Anthocyanins contributed more to the antioxidant activity of all fruits (90%) than flavonols, flavan-3-ols and phenolic acids (10%). A biphasic reaction was observed between DPPH • radicals and phenols, with 'fast' and 'slow' scavenging rates which might be important in the biological activity of these fruits. Sour cherries and blackberries which stand out with the highest total phenol content (1416 and 1040 mg kg )1 ) had also the strongest antioxidant activity (EC 50 = 807 and 672 g of fruit per gram of DPPH) and can be considered as good source of dietary phenols.

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This study was aimed to investigate the influence of solvent (water and ethanol in concentration: 50%, 70% and 96%) and extraction temperature (25-80)°C on polyphenols extraction of grape seed (Vitis vinifera L. cv. ''Frankovka'') cultivated in Eastern Croatia. The best results were reached using 50% ethanol at 80°C. The most abundant individual polyphenolic compound was catechin which makes the average of 45.11% of the total phenolic content followed by epicatechin (34.45%), procyanidin B 2 (12.90%), gallic acid (5.34%), gallocatechin (1.58%), epicatechin gallate (1.01%). The antioxidant activity of extracts was determined by DPPH-method and it was highly dependent on extraction solvent and temperature. The total extractable proanthocyanidins content of extract had the highest positive correlation (r = 0.994) with antioxidant activity, which indicated that these compounds might be the most important antioxidant in examined grape seed extracts. Relationship between phenolic content and colour of extracts was observed.

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Electrochemical oxidation of (À)-epigallocatechin gallate (EGCG), the main monomer flavanol found in green tea, has been investigated over a wide pH range at a glassy-carbon electrode using square-wave voltammetry (SWV). Square-wave voltammograms of (À)-epigallocatechin (EGC) and gallic acid have been studied as well. The I -E profile of EGCG, i.e. the oxidation potentials and the current responses of the first and the second peak, is pH dependent. The oxidation of EGCG is a quasireversible process over the studied pH range, which was also confirmed by the non-linear relationship between the peak currents and squre root of frequency. The best SWV responses for EGCG were obtained at pH 2.0, frequency of 100 Hz, step of 2 mV and amplitude of 50 mV. Under these conditions, linear responses for EGCG were obtained for concentrations from 1 Â 10 À7 M to 1 Â 10 À6 M, and calculated LOD and LOQ for the first oxidation peak were 6.59 Â 10 À8 M and 2.19 Â 10 À7 M, respectively. The proposed electroanalytical procedure was applied for the determination of EGCG content in green tea. Developed SWV methodology represents a potential analytical tool in determination of catechins in tea samples.

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