Production of antioxidants from Eucalyptus globulus wood by solvent extraction of hemicellulose hydrolysates

Eucalyptus globulus wood samples were subjected to acid prehydrolysis, and the ethyl acetate-soluble fraction of hydrolysis liquors was assayed for antioxidant activity. The total yield was measured gravimetrically, the yield in phenolics was determined in terms of gallic acid equivalents, and the antioxidant activity was measured, using both the DPPH test for radical scavenging capacity and the inhibition of β-carotene bleaching assay. Up to 0.43 g of gallic acid equivalents/100 g dry wood were recovered by ethyl acetate extraction. The antioxidant activity of this fraction (EC50=0.39 g/l) corresponded to 61% of that presented by BHA, and was 12 times higher than that of BHT. When the acid hydrolysis was carried out under conditions leading to extracts with maximal antioxidant specific activity, the EC50 (0.23 g/l) was comparable to that of BHA. The freeze-dried extracts were stable for two months at 4 °C in the darkness, whereas the antioxidant capacity was reduced by 30 and 48% after 2 months storage at 40 and 50 °C, respectively. The aqueous phase, after ethyl acetate extraction of hydrolysates, was suitable for use as a xylose-based fermentation medium.