Production of oligosaccharides by autohydrolysis of breweryÕs spent grain F. Carvalheiro a , M.P. Esteves a , J.C. Paraj  o b , H. Pereira c , F.M. G  ırio a, * a Departamento de Biotecnologia, INETI, Estrada do Pac ßo 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 T ecnica de Lisboa, 1349-017, Lisboa, Portugal Received 8 October 2002; received in revised form 17 February 2003; accepted 5 April 2003 Abstract BreweryÕs spent grain was treated with water in a process oriented towards the production of xylo-oligosaccharides (XOS). A wide range of temperatures and reaction times were tested and the effects of these operational variables on hemicellulose solubi- lization and reaction products were investigated. The maximal XOS yield (61% of the feedstock xylan) was obtained at 190 °C after 5 min of reaction. Several oligosaccharide mixtures with different molecular weight distributions were obtained depending on temperature and reaction time. Longer reaction times led to decreased oligosaccharide production and enhanced concentrations of monosaccharides, sugar decomposition products and acetic acid. With reaction times leading to the maximal yields of XOS, little decomposition into organic acids and aldehydes was found at all the temperatures assayed. From the composition of processed solids, it was calculated that 63–77% of the initial xylan was selectively solubilized in autohydrolysis treatments. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Xylo-oligosaccharides; Hydrothermal treatments; Autohydrolysis; BreweryÕs spent grain 1. Introduction BreweryÕs spent grain (BSG) is a residue from the brewery industry obtained after liquefation and sac- charification of the barley starch fraction. This ligno- cellulosic residue is a hemicellulose-rich material mainly used as cattle feed, although its market is variable and of low added value. The use of both chemical hydrolysis and steam ex- plosion technologies for biomass conversion into useful chemicals, energy and food has been considered for fractionation of biomass components (Koukios, 1985; Montan e et al., 1998; Shimizu et al., 1998; Li et al., 2000a). Recently, more environmental-friendly techno- logies, such as autohydrolysis, have gained interest (Tortosa et al., 1995; Weil et al., 1998; Garrote et al., 1999a,b). Autohydrolysis has been mainly used as a pretreatment to make cellulose more amenable to fur- ther enzymatic saccharification (H€ ormeyer et al., 1988; Heitz et al., 1991; Weil et al., 1998; Meunier-Goddik et al., 1999) but could also be a promising technology for converting agro-food by-products into useful food in- gredients, e.g., functional oligosaccharides (OS). Since no chemicals other than water are used, several advantages have been associated with this process in respect to acid prehydrolysis, namely low by-product generation, limited problems derived from equipment corrosion owing to the mild pH of reaction media and reduction of operational costs since no further neutralisation is needed. Moreover, this mild technology allows an almost quantitative re- covery of hemicelluloses as soluble OS (Bouchard et al., 1991; Garrote et al., 1999b). Some of these OS have functional properties prone to be used as food ingredi- ents. Inulin type-fructans, which include native inulin, enzymatically hydrolysed inulin or oligofructose and synthetic fructo-oligosaccharides (FOS) are the most studied OS and their probiotic effect on growth of the colon beneficial bacteria has been demonstrated (Gibson and Wang, 1994; Gibson and Roberfroid, 1995; McBaine and Macfarlane, 1997; Roberfroid et al., 1998; Van Loo et al., 1999). A probiotic effect has also been ascribed to xylo-oligosaccharides (XOS) (Modler, 1994; Jeong et al., 1998; Suwa et al., 1999) although their use and produc- tion are not widespread. Imaizumi et al. (1991) observed * Corresponding author. Tel.: +351-217165141; fax: +351- 217163636. E-mail address: francisco.girio@ineti.pt (F.M. G  ırio). 0960-8524/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0960-8524(03)00148-2 Bioresource Technology 91 (2004) 93–100