Short Communication High pressure treatment as a tool for engineering of enzymatic reactions in cellulosic fibres Sandra C.T. Oliveira a , Andreia B. Figueiredo a , Dmitry V. Evtuguin a,⇑ , Jorge A. Saraiva b a CICECO, Chemistry Department, University of Aveiro, Campus de Santiago, P-3810-193 Aveiro, Portugal b QOPNA, Chemistry Department, University of Aveiro, Campus de Santiago, P-3810-193 Aveiro, Portugal article info Article history: Received 4 September 2011 Received in revised form 14 December 2011 Accepted 16 December 2011 Available online 24 December 2011 Keywords: Kraft pulp Xylan Enzymatic hydrolysis High hydrostatic pressure treatment Xylanase abstract Ultrahigh hydrostatic pressure (UHP) was applied to enhance the enzymatic hydrolysis of xylan in cellu- losic fibers. The pretreatment improved xylan accessibility in the fiber cell wall and a 5–10-fold increase in the initial hydrolysis rate of xylan by xylanase was observed when Eucalyptus globulus kraft bleached pulp was pretreated at hydrostatic pressures of 300–400 MPa for 15–45 min. The rate and the extent of hydrolysis can be controlled by varying the pressure and the exposure time of UHP treatment prior to enzymatic hydrolysis. Sequential UHP pretreatment and hydrolysis by xylanase disaggregated the hydrated cellulose fibrils and led to the gelation of cell wall regions accessible to enzymatic attack. UHP could therefore become a tool for the engineering of enzymatic reactions within cellulosic fibers to obtain products with tailored properties. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Plant fibers are a renewable resource for various biomaterials and may be used either in their natural state or after physical, physico-chemical or chemical modifications (Fomin, 2001). The properties of cellulosic fibers are predetermined by the structural organization of their macromolecular components. Besides the major component, cellulose, hemicelluloses play an important role in fiber properties. Hemicelluloses are structural polysaccharides that define the spatial organization of cellulose microfibrils (CMF). In the so-called xylan-type cell wall (all angiosperms), heteroxylan envelops CMF, fills interfibrillar spaces and is linked to lignin thus providing cell wall integrity (Beg et al., 2001). In delignified cellulosic fibers (chemical pulp) targeted for papermaking or chemical processing, the amount of xylan is strictly controlled. The xylan content in fibers affects their bleach- ability (Suurnäkki et al., 1997), beatability, physical properties upon drying (hornification) (Rebuzzi and Evtuguin, 2006), accessi- bility towards cellulolytic enzymes (Eremeeva et al., 2001), and chemical processability into diverse derivatives (Christov and Prior, 1993; Gehmayr et al., 2011). Hence, different grades of cellu- losic pulps can be obtained by regulating their xylan content. In practice this is done by choosing an appropriate delignification procedure and particular cooking and bleaching conditions with- out much inflexibility. The selective gradual removal of xylan by hemicellulases may allow targeted modification of cellulose fibers for different applications. Hemicellulases have been used increasingly in the pulp and paper industry, mainly due to their ability to modify cellulosic fibers for a wide range of applications (Bajpai, 1999; Beg et al., 2001; Savitha et al., 2009). Xylanases are applied in biobleaching of chemical kraft pulps, since the enzymatic treatment improves pulp accessibility towards the oxidation by bleaching chemicals, thus minimizing chlorine consumption (Beg et al., 2001; Savitha et al., 2009; Suurnäkki et al., 1997). Additionally, xylanase treatment of kraft pulps has proven to increase the leachability of lignin and therefore to facilitate the delignification process (Suurnäkki et al., 1997). Besides applications in the form of cellulose ethers/esters, xylans-free cellulose is suitable for the production of dissolving pulps whose hemicelluloses content is strictly limited (Christov and Prior, 1993; Gehmayr et al., 2011). After partial removal of xylan from cellulosic pulps, the resultant xylose from the enzymatic hydrolysis can be used either for bioethanol processing or converted into high value-added chemicals, such as xylitol, furfural or lactic acid (Balat, 2011; Dhepe and Sahu, 2010). However, the practical realization of such applications is hin- dered by poor hydrolysis of xylan in cellulosic fibers due to problems associated with accessibility in the fiber cell wall (Alvira et al., 2010; Kaya et al., 2000). In order to improve enzymatic digestibility of xylan, several pre-treatment methodologies have been developed. These include biological, mechanical, thermal or physico-chemical pretreatments able to diminish the structural order of cell wall com- ponents and compositional constraints of lignocellulosic materials 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.12.093 ⇑ Corresponding author. Tel.: +351 234 401 526; fax: +351 234 370 084. E-mail address: dmitrye@ua.pt (D.V. Evtuguin). Bioresource Technology 107 (2012) 530–534 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech Article 44