Valorização das cascas de espécies arbóreas da Amazônia como fonte de taninos e seu uso como antioxidantes naturais

Abstract

The bark of trees is a potential source of byproducts with multiple uses that can add value to a species and contribute to its sustainable management. Thus, the main objective of the study was to deepen knowledge about the anatomical and chemical composition of the barks of five forest species from the Amazon and to evaluate the potential of their barks as a source of tannins for use as naturais antioxidants. The barks of the species Byrsonima spicata, Croton matourensis, Myrcia splendens, Tapirira guianensis and Vismia guianensis were collected in secondary forests located in the state of Pará, Brazil. The anatomy of the species was detailed for the first time by describing the histological sections and analyzing the biometry of the cellular elements. The barks were characterized in terms of histochemistry, extractive content, suberin, lignin, polysaccharides and minerals. The polyphenols were quantified by high- performance liquid chromatography. The antioxidant activity of the tannins extracted from the bark of each species against the free radical 2,2-diphenyl-1-picryl hydrazyl hydrate (DPPH) was determined and compared to that of commercial black wattle tannin and the commercial synthetic antioxidant butylated hydroxytoluene (BHT). The anatomical structure of the barks showed the presence of a rhytidome composed of one to seven layers of periderms with small phellem development. The bark had a significant presence of extractives (from 29.3 to 46.1%) mostly of compounds that were soluble in ethanol and water. Suberin content was low (from 0.4 to 3.4%) and lignin ranged from 19.0 to 33.4%. Ash varied from 1.8 to 6.0% and the barks were particularly rich in calcium (2.9 to 20.6 g kg -1 of bark). Six phenolic compounds were identified, with the highest concentrations of catechin and gallic acid in most of the extracts. A rich presence of condensed tannins was observed in the bark, especially in B. spicata (19.1%) and M. splendens (29.9%). The anatomical and histochemical study showed that the tannins are located mainly in the cells of the periderm, the outermost region of the bark, which contributes to the sustainable management of the trees. The tannins showed high antioxidant activity against the DPPH free radical. The highest antioxidant activities were found in the tannins of B. spicata (95.4%), T. guianensis (95.2%) and M. splendens (92.1%), higher than commercial tannin (72.6%) and the antioxidant BHT (87.9%). Thus, by characterizing the bark, it was possible to learn about the chemical value of five forest species from the Amazon biome, and the potential of their tannins for use as natural antioxidants.