Process Biochemistry 40 (2005) 1215–1223 Evaluation of the detoxification of brewery’s spent grain hydrolysate for xylitol production by Debaryomyces hansenii CCMI 941 F. Carvalheiro a , L.C. Duarte a , S. Lopes a , J.C. Parajó b , H. Pereira c , F.M. G´ ırio a,∗ a Departamento de Biotecnologia, INETI, Estrada do Paço do Lumiar 22, 1649-038 Lisboa, Portugal b Universidade de Vigo-Ourense, As Lagoas, 32004 Ourense, Spain c Centro de Estudos Florestais, Instituto Superior de Agronomia, Universidade Técnica de Lisboa, 1349-017 Lisboa, Portugal Received 24 July 2003; received in revised form 2 April 2004; accepted 18 April 2004 Abstract The hemicellulose fraction of brewery’s spent grain was selectively hydrolyzed by two sequential steps, autohydrolysis and post-hydrolysis (with diluted sulfuric acid), in order to obtain a fermentable hydrolysate. The concentrations of monosaccharides and inhibitory by-products generated by these sequential processes were evaluated and several detoxification methods for inhibitors removal were tested. These methods included pH adjustment to 5.5, overliming, adsorption into activated charcoal and treatment with anion- and cation-exchange resins at different pH. The treatment of the raw hydrolysate with anion-exchange resins without previous pH correction was found to be the method that removed more inhibitory compounds. Detoxification effects in both non-concentrated and concentrated hydrolysates were evaluated for Debaryomyces hansenii biomass and xylitol production, respectively. When supplemented with inorganic salts and vitamins, the detoxified hydrolysates (through anion-exchange resins) showed lower biomass yield and only slightly higher volumetric productivity (11%) compared to the non-detoxified (pH-adjusted) hydrolysates. The best xylitol yields (0.51 and 0.50 g g -1 ) and productivities (0.29 and 0.33 g l -1 h -1 ) were found both in non-detoxified and detoxified with activated charcoal hydrolysates, respectively. © 2004 Elsevier Ltd. All rights reserved. Keywords: Autohydrolysis; Brewery’s spent grain; Acid post-hydrolysis; Detoxification; Xylitol; Debaryomyces hansenii 1. Introduction Lignocellulosic biomass from forests, agricultural and agro-industrial residues is a widespread and inexpensive source of polysaccharides. The integrated utilization of this resource depends on the degradation of these polymers to sugars, with hemicelluloses being important in the overall conversion process. Brewery’s spent grain (BSG) is a hemi- cellulose rich agro-industrial by-product, whose hemicellu- loses can be hydrolyzed by acids or enzymes to produce a mixture of sugars that are potential substrates for conversion to a variety of added-value products such as xylitol. Dilute-acid hydrolysis is a simple and rapid method and is commonly used for the hydrolysis of biomass [1]. When ∗ Corresponding author. Tel.: +351-210924721; fax: +351-21-7163636. E-mail address: francisco.girio@ineti.pt (F.M. G´ ırio). agricultural residues or hardwoods are used as raw mate- rials, xylose is the most abundant sugar in hydrolysates. Unfortunately, the sugar liquors obtained also contain sev- eral microbial inhibitors, which can be included in three main groups: furan derivatives, aliphatic acids and phe- nolic compounds. Furan derivatives include furfural that results from the degradation of pentoses, and hydrox- ymethylfurfural (HMF), that results from the degradation of hexoses. HMF can be further degraded to levulinic acid and formic acid, the latter also formed when fur- fural is broken down. Acetic acid, the major aliphatic acid present, is released from the hemicellulosic acetyl groups. During the acid hydrolysis, a minor part of lignin is also degraded to a wide range of aromatic compounds being the low molecular mass phenolics the most toxic [2–4]. Autohydrolysis is an alternative method for the depoly- merization of hemicelluloses, with several advantages over 0032-9592/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.procbio.2004.04.015