Non-isothermal autohydrolysis of barley husks: Product distribution and antioxidant activity of ethyl acetate soluble fractions G. Garrote, J.M. Cruz, H. Domı ´nguez * , J.C. Parajo ´ Departamento de Enxen ˜erı ´a Quı ´mica, Universidade de Vigo (Campus Ourense), Edificio Polite ´cnico, As Lagoas, 32004 Ourense, Spain Received 18 January 2007; received in revised form 29 May 2007; accepted 5 June 2007 Available online 14 July 2007 Abstract Non-isothermal treatments of barley husks in aqueous media were performed under a variety of operational conditions, to cause the hydrolytic degradation of hemicelluloses. The amount and composition of solid and liquid phases were determined. Liquors from treat- ments were extracted with ethyl acetate in order to remove non-saccharide components (mainly derived from the extractive acid-soluble lignin fractions), and the extracted fractions were quantified and assayed for antioxidant activity using the DPPH radical scavenging test. Posthydrolysis of autohydrolysis liquors led to xylose-containing solutions suitable as fermentation media. The dependence of the major process parameters (concentrations of monosaccharides and monosaccharide-degradation products obtained after autohydrolysis–pos- thydrolysis, yield of ethyl acetate soluble compounds and antioxidant activity of isolates) on the severity of treatments was assessed. The ethyl acetate soluble fraction obtained under the best processing conditions showed an antioxidant activity in the range reported for syn- thetic antioxidants. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Barley husks; Autohydrolysis; Fermentable sugars; Ethyl acetate extracts; Antioxidant activity 1. Introduction Aqueous processing under mild conditions (autohydro- lysis reaction, usually carried out at temperatures in the range 160–250 °C) is an environmentally friendly technol- ogy for biomass utilisation (Garrote, Domı ´nguez, & Parajo ´, 1999). The catalytic species (hydronium ions) com- ing from water autoionisation and from in situ generated organic acids cause the hydrolytic degradation of hemicel- luloses, leading to liquors containing a mixture of sugar oligomers, monosaccharides, sugar-decomposition prod- ucts (such as furfural or hydroxymethylfurfural, HMF) and acetic acid (from acetyl group hydrolysis). As the reac- tion is not selective, other compounds (including those derived from extractives and acid-soluble lignin) are also present in liquors. The solid phase from treatments is enriched in cellulose, which is hardly altered during auto- hydrolysis, enabling its further utilisation for a variety of purposes. Solvent extraction of autohydrolysis liquors allows the selective removal of non-saccharide compounds. Because of this, ethyl acetate treatments have been employed for refining liquors containing xylooligosaccharides, which can be used as ingredients for functional foods (Vegas, Alonso, Domı ´nguez, & Parajo ´, 2005). Alternatively, if the autohydrolysis media are posthydrolysed to give fermenta- tion media, the absence of ethyl acetate soluble compounds is expected to improve their fermentability (Rivas, Domı ´n- guez, Domı ´nguez, & Parajo ´, 2002). In this context, the development of practical applications for the ethyl acetate soluble compounds present in autohydrolysis liquors based on their antioxidant activity has been proposed (Garrote, Cruz, Domı ´nguez, & Parajo ´, 2003). 0260-8774/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2007.06.021 * Corresponding author. Tel.: +34 988 387082; fax: +34 988 387001. E-mail address: herminia@uvigo.es (H. Domı ´nguez). www.elsevier.com/locate/jfoodeng Journal of Food Engineering 84 (2008) 544–552