Caracterização anatômica e química de cascas de espécies amazônicas como fonte de antioxidantes naturais

Abstract

The general objective was to characterize the stem barks of the tree species Schizolobium parahyba var. amazonicum, Zanthoxylum ekmanii and Protium tenuifolium that occur in areas of sustainable management in the Brazilian Amazon, considering the potential use of their barks as a source of phenolic compounds for application in natural antioxidants. The species' barks were collected from eight individuals in a sustainable management area in the municipality of Dom Eliseu, Pará State, Brazil. The anatomical characterization consisted of macroscopic and microscopic analysis of the bark. Measurement of the cells was performed by dissociating the macerated bark of the species. The barks were further characterized for somatic chemistry, mineral components, phenolic compounds, and antioxidant activity. Tannic extracts were obtained from the barks with and without addition of 3% Na2SO3 (sodium sulfite) in relation to dry mass and their yields of condensed tannins determined by the Stiasny index. It was observed that the barks of S. parahyba. var. amazonicum, Z. ekmanii and P. tenuifolium are formed by conductive phloem, non-conductive phloem and rhytidome. The barks of S. parahyba var. amazonicum, Z. ekmanii showed a large amount of clusters of sclereids, and P. tenuifolium had a high amount of secretory cells. In the species S. parahyba var. amazonicum there were astrochlereids. The main chemical results showed that the bark extracts of S. parahyba var. amazonicum presented 0.67% of condensed tannins in water extraction and 1.81% with the addition of Na2SO3 (sodium sulfite). S. parahyba var. amazonicum showed 0.80% and 1.24%, respectively. In P. tenuifolium the values for the two extraction conditions were 5.1% and 8.1%, respectively, which were higher than the other species. Regarding the results of antioxidant activity, the IC5O values of the extract of S. parahyba var. amazonicum were higher compared to the commercial antioxidant butylated hydroxytoluene (BHT), indicating that the bark needed a greater amount of extract to inhibit 50% of the 2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH) free radicals, however in other sample concentrations it was observed that the bark extract showed higher antioxidant activity than the BHT, the same was observed in Z. ekmanii bark extracts. The extracts of P. tenuifolium bark presented IC5O values higher compared to the commercial antioxidant butylated hydroxytoluene (BHT), indicating that the concentration was insufficient to inhibit 50% of the free radicals 2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH), however, in all concentrations of samples of P. tenuifolium bark extract, the antioxidant activity was higher than the BHT. At the concentration of 25 μg mL - 1, the bark extract achieved 83.5% inhibition against the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), while BHT inhibited only 75.0%.