Solvent extraction of hemicellulosic wood hydrolysates: a procedure useful for obtaining both detoxified fermentation media and polyphenols with antioxidant activity

Eucalyptus wood hydrolysates were extracted with organic solvents (ethyl acetate and diethyl ether) to remove part of the phenolics derived from lignin. In order to obtain increased phenolic removal, the effects of the major experimental variables affecting extraction (type of solvent, hydrolysate to solvent volume ratio, temperature, pH and coupling of extraction stages) were explored. Under the best operational conditions, up to 84% of the initial lignin-derived compounds were extracted. The phenolic compounds extracted by solvents showed antioxidant activity. Under the best conditions, the antioxidant activity coefficient was 64% of the value found with a synthetic antioxidant (BHT). Extracted hydrolysates led to xylose solutions, allowing an enhanced fermentative production of xylitol with the yeast Debaryomyces hansenii.