Characterization of the bark of Protium tenuifolium Engl. from the Amazonian biome as a source of natural antioxidants

Abstract

The bark anatomy was analysed, as was the overall chemical composition (extractives, lignin, suberin, ash and polysaccharides), and a quantitative elemental analysis was performed of the bark and two tannin extracts (extracted with water only and with a mixture of water and Na2SO3). The phenolic composition and antioxidant activity of the bark extracts were quantified. The results indicated that the bark is composed of conductive phloem, nonconductive phloem, rhytidome, crystals and secretory cells. The average chemical composition was 15.9 % extractives, 35.3 % total lignin, 1.9 % suberin, 15.4 % ash and 31.5 % polysaccharides. The condensed tannin yield in the extract obtained with water alone was 5.1 %, and that in the treatment with water and Na2SO3 was 8.1 %. The ethanol-water extract had a high phenolic content (112.6 mg GAE g−1 extract). The bark extract showed strong antioxidant activity, reaching 83.5 % inhibition of DPPH free radicals, which was higher than the value of 75.0 % for the commercial antioxidant BHT at the same concentration. These results demonstrate that Protium tenuifolium is a potential natural Amazonian source of phenolic compounds and antioxidants and can be used for medicinal purposes and the production of various sustainable products, such as cosmetics.