Tannin extraction and characterization of polar extracts from the barks of two eucalyptus urophylla hybrids

Abstract

Barks from two commercial clones of Eucalyptus urophylla hybrids used by the charcoal industry in Brazil were analyzed, with their polar extracts characterized. Also, tannins were extracted with water and sodium sulfite. The mean bark chemical composition showed 2.6% ash, 16% extractives (89% of which were polar extractives), 1.2% suberin, 18.9% lignin, and 61.4% polysaccharides composed mainly of glucans (glucose 48.3% of bark) and xylans (xylose plus arabinose 10.1% of bark). The polar extracts included high mean contents of total phenolics (380.9 mg GAE / g extract), flavonoids (178.4 mg CE / g extract), and tannins (67.7 mg CE / g extract). The mean antioxidant activity of the extracts was low (53.6 mg Trolox / g of bark extract). The extracts had Stiasny indices of 20% with water and 45% with sodium sulfite solution. The FTIR spectra showed condensed tannin bands characteristic of C=C, C-C, and O-H bonds. The barks of E. urophylla hybrids are a potential source of polar extractives that may represent an important valorization.