Industrial Crops and Products 52 (2014) 544–551 Contents lists available at ScienceDirect Industrial Crops and Products journa l h om epa ge: www.elsevier.com/locate/indcrop Investigation on the structure and antioxidant properties of modified lignin obtained by different combinative processes of oil palm fronds (OPF) biomass M. Hazwan Hussin a,b , Afidah Abdul Rahim a , Mohamad Nasir Mohamad Ibrahim a , Mehdi Yemloul c , Dominique Perrin b , Nicolas Brosse b,∗ a Lignocellulosic Research Group, School of Chemical Sciences, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia b Laboratoire d’Etude et de Recherche sur le MAteriau Bois (LERMAB), Faculte des Sciences et Techniques, Universite de Lorraine, Bld des Aiguillettes, F-54500 Vandoeuvre-les-Nancy, France c CRM2 UMR 7036, Universite de Lorraine, Bld des Aiguillettes, F-54500 Vandoeuvre-les-Nancy, France a r t i c l e i n f o Article history: Received 4 September 2013 Received in revised form 12 November 2013 Accepted 17 November 2013 Keywords: Organosolv lignin Oil palm fronds Autohydrolysis 2-Naphthol Antioxidant a b s t r a c t The present work reports on the structural characteristic and antioxidant activity of the ethanol organo- solv lignin obtained from oil palm fronds (OPF) via different pretreatment combinative processes. Physicochemical analyses of pretreated lignins have shown that autohydrolysis method prior to organo- solv pulping gave smaller fragments of lignin with higher phenolic hydroxyl content compared to dilute sulphuric acid method. Indeed, repolymerization tends to occur during dilute sulphuric acid pretreat- ment, affecting its lignin structure and antioxidant activity. Chemical modification of lignin by utilizing organic scavenger (2-naphthol) seems to improve the properties of lignin by reducing the possibility of condensation reaction. Oxygen uptake measurement has shown that the antioxidant activity of the dif- ferent pretreated organosolv lignins (autohydrolyzed lignin, AH EOL: 82% > autohydrolyzed + 2-naphthol lignin, AHN EOL: 78% > dilute sulphuric acid treated lignin, DAP EOL: 75%) were closely related to its average molecular weight and phenolic hydroxyl content. © 2013 Published by Elsevier B.V. 1. Introduction Large amounts of lignin are produced each year by the pulp and paper industry as by-products of delignification. However, the pulping processes currently used in the paper industry pro- duce degraded lignin employed in low-added value utilizations and energy production. Worldwide, several types of technologies have been studied and proposed for the purpose of production of second generation bioethanol from lignocellulosic feedstock. To improve the overall effectiveness of bioethanol production, one strategy is the biorefinery model in which all components of biomass are fully used to produce a wide range of value-added products (Ragauskas et al., 2006). Organosolv processes which allow a clean fractionation of lignocellulosic feedstocks and the recovery of high- quality lignins (relatively pure, less condensed than other industrial lignins, sulphur free, soluble in organic solvent) are of great inter- est and are currently a focus of attention (Zhao et al., 2009). Thus, availability of such organosolv lignin fractions in large quantities should stimulate development in new lignin utilizations. However, ∗ Corresponding author. Tel.: +33 3 83 68 48 62; fax: +33 3 83 68 44 98. E-mail address: Nicolas.Brosse@lermab.uhp-nancy.fr (N. Brosse). the valuable utilization of the lignin produced at the industrial scale requires a good control of its variability which is a function of the nature of the raw material and also of the processes used for the lignin extraction (Brosse et al., 2011). Lignins as well as other polyphenols are potent free radical scavengers and considered to be valuable source of antioxidant phenolic compounds. One of the analytical methods used to mea- sure the antioxidant capacity is based on the inhibition of the oxidation of organic substrates (Burton et al., 1985; Wanasundara and Shahidi, 1994; Eloualja et al., 1995). The oxygen uptake mea- surement is the most direct method used to measure the reaction extent (Poaty et al., 2010; Saha et al., 2013). Moreover, the induced oxidation of methyl linoleate and its radical long chain reaction is well known to be inhibited by various antioxidants (Uri, 1961). The applicability of lignins from different sources as antioxidants has been also successfully tested (Urgatondo et al., 2009). Recent stud- ies by Garcia et al. (2010) have revealed the effect of pretreated processes of lignin on its antioxidant capacity. Combinative pretreatments of lignocellulosic feedstocks involv- ing a prehydrolysis step to hydrolyze the hemicelluloses and a second step (where the solid from the 1st step is pretreated again) have been recently described. The main goal of the 2-step processes is to minimize the degradation of carbohydrate fragments into 0926-6690/$ – see front matter © 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.indcrop.2013.11.026