Abstract

The phenolic content and antioxidant activities of extracts from Quercus durifolia, Quercus resinosa, Quercus eduardii and Quercus sideroxyla leaves were studied. Extracts were obtained by successive extraction with aqueous acetone (70%) followed by methanol (50%). Antioxidant activities were determined using a single electron transfer (SET) and hydrogen atom transfer (HAT) based assays. For SET-based the assays performed were, 2,2-diphenyl-1-picryl hydrazine (DPPH) inhibition expressed as IC₅₀, redox potential, as mV, inhibition of the low density lipoprotein (LDL) oxidation, as % of inhibition. For HAT-based assay, crocin bleaching technique was applied; a kinetics approach was used for the evaluation of total antioxidant capacity and the results presented in terms of equivalence by weight of a reference antioxidant. Acetone extracts (PFQA) from leaves of all Quercus species showed the best antioxidant capacity. Q. resinosa (PFQr) exhibited the best antioxidant capacity among the Quercus species analyzed either in acetone or methanol extracts (PFQM). Distinctive results are: DPPH IC₅₀, PFQrA = 78.3 µg/g, PFQrM = 250.7 µg/g; In Redox potential, PFQrA = 147.0 mV, PFQrM = 201.6 mV; In LDL oxidation inhibition: 98.2% and in inhibition of crocin bleaching, PFQrA = 1.08 g, PFQrM = 0.98 g. In conclusion, Quercusleaves might be used as potential source of polyphenolic antioxidants.

Key words: Quercus sp., SET-based assay, HAT-based assay, phenolic compounds, antioxidant activity.