Profiling of Phenolic Compounds and Antioxidant Activity of Dry Extracts from the Selected Sorbus Species

The antioxidant efficiency of dry extracts from inflorescences and/or leaves of seven Sorbus species was studied using four in vitro tests of SET (single electron transfer) and HAT-type (hydrogen atom transfer) mechanisms. The 70% methanol extracts and its diethyl ether, ethyl acetate, n-butanol and water fractions were tested in parallel with the phenolic standards, e.g., caffeic acid, quercetin, BHA, BHT, and Trolox((R)). The SET-type activity of the extracts depended primarily on the extraction solvent. The most valuable extracts were n-butanol and ethyl acetate ones, which activity was high in the DPPH (EC50 = 3.2-5.2 mu g/mL), TEAC (2.8- 4.0 mmol Trolox((R))/g), and FRAP (9.8- 13.7 mmol Fe2+/g) tests, and strongly correlated with the total phenolic levels (39.6- 58.2% of gallic acid equivalents). The HPLC-PDA analysis of the extracts led to the identification of chlorogenic acid, isoquercitrin, hyperoside, rutin, quercetin 3-O-sophoroside, and sexangularetin 3-O-beta-D- glucopyranoside as the main components. Apart from flavonoids and hydroxycinnamic acids, proanthocyanidins have also a significant impact on the SET-type activity. The HAT-reactivity of the extracts in the linoleic acid peroxidation test (IC50 = 36.9-228.3 mu g/mL) depended more strongly on the plant tissue than on the extraction solvent, and its correlation with the phenolic content was weak. Both SET and HAT-type activity of the most potent Sorbus extracts was comparable with the activity of the standards, indicating their great potential as effective sources for health products.