Comparative study of antioxidant capacity of yellow birch twigs extracts at ambient and high temperatures

The antioxidant capacity of yellow birch (Betula alleghaniensis Britton) twigs aqueous acetone extract and its fractions was evaluated at ambient and at elevated temperatures. The crude extract, obtained by maceration in acetone, was further fractionated with tert-butyl-methyl ether and ethyl acetate. The antioxidant activity at room temperature was studied by methods based on 1,1-diphenyl-2-picrylhydrazyl (DPPH). Differential scanning calorimetry (DSC) and thermogravimetry (TG) were employed at high temperatures. The commercial antioxidant 2,6-di-tert-butyl-4-methyl-phenol (BHT) was used as a reference. Among samples, the ethyl acetate and aqueous fractions exhibited the highest antioxidant capacity in DPPH assays. The ether fraction and crude extract showed more antioxidant activity at high temperatures. The commercial antioxidant BHT exhibited the best antioxidant behaviour in most of the reported tests. The only exception was in the kinetic method with DPPH. The results of this study confirm that antioxidant activity is a property that strongly depends on the oxidation conditions used in the particular oxidation test.