Enzyme and Microbial Technology 44 (2009) 17–23 Contents lists available at ScienceDirect Enzyme and Microbial Technology journal homepage: www.elsevier.com/locate/emt Enhancement of the enzymatic digestibility of sugarcane bagasse by alkali–peracetic acid pretreatment Xuebing Zhao a,∗ , Feng Peng b , Keke Cheng c , Dehua Liu a,∗∗ a Institute of Applied Chemistry, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China b College of Science, Hunan Agricultural University, Changsha 410028, China c Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, China article info Article history: Received 28 May 2008 Received in revised form 21 July 2008 Accepted 29 July 2008 Keywords: Sugarcane bagasse Pretreatment Alkaline swelling Peracetic acid Delignification Enzymatic digestibility abstract The enzymatic digestibility of sugarcane bagasse was greatly increased by alkali (NaOH)–peracetic acid (PAA) pretreatment under mild conditions. The effects of several factors affecting the pretreatment were investigated. It was found that when bagasse was pre-pretreated by 10% (based on initial dry materials) NaOH with 3:1 liquid-to-solid ratio at 90 ◦ C for 1.5 h and further delignified by 10% peracetic acid (based on initial dry materials) at 75 ◦ C for 2.5 h, the yield of reducing sugars reached 92.04% by enzymatic hydrolysis for 120 h with cellulase loading of 15 FPU/g solid. Compared with acid and alkali pretreatment, alkali–PAA pretreatment could be conducted under milder conditions and was more effective for delignification with less carbohydrates being degraded in the pretreatment process. Alkaline stage played an important role for partial delignification, swelling fibers and subsequently reducing PAA loading. No loss of cellulase activity (FPA) was observed in the liquid phase for alkali–PAA pretreated bagasse after enzymatic hydrolysis for 120 h. © 2008 Elsevier Inc. All rights reserved. 1. Introduction During last years, environmental concerns and energy source shortage have increased the interest of using ethanol as an alterna- tive transportation fuel. However, it is not sustainable to produce ethanol from grains such as corn and wheat in China and some other countries. Lignocellulosic materials are attractive feedstocks for ethanol production since they are abundant and cheap. One of the major lignocellulosic materials to be considered in tropical countries is sugarcane bagasse, the fibrous residue obtained after extracting the juice from sugarcane in the sugar production process [1]. In the bioconversion of lignocellulosic biomass to fermentable sugars, the raw biomass should undergo pretreatment to increase its enzymatic digestibility. The final purpose of pretreatment is to realize high sugar yields from the overall process at low cost, but the specific goal of the pretreatment for increasing the enzymatic digestibility is to remove lignin and hemicelluloses, disrupt the cel- lulose crystallinity, and increase the porosity of the materials to make cellulose more accessible to the cellulases [2,3]. Several pro- ∗ Corresponding author. Tel.: +86 10 62782654; fax: +86 10 62785475. ∗∗ Corresponding author. Tel.: +86 10 62792128; fax: +86 10 62792128. E-mail addresses: zhaoxb04@mails.tsinghua.edu.cn (X. Zhao), dhliu@tsinghua.edu.cn (D. Liu). cesses have been developed for pretreatment of sugarcane bagasse, including steam explosion [4,5], liquid hot water process [6], acid hydrolysis [7], alkali pretreatment [8,9] and wet oxidation [1]. All of these processes enhanced the enzymatic digestibility of bagasse to a certain extent. Our previous work showed that the enzymatic hydrolysis of sugarcane bagasse could be greatly enhanced by per- acetic acid (PAA) pretreatment [10], which was achieved mainly by delignification accompanying with the increase of the surface area and exposure of cellulose fibers [11]. It was also found that under a mild condition removal of lignin was much more help- ful than removal of hemicellulose for increasing the enzymatic digestibility of sugarcane bagasse [11]. Therefore, the main purpose of chemical pretreatment under mild condition (<100 ◦ C) is delig- nification and separating cellulose fibers. However, single-stage PAA pretreatment consumed too much PAA (50% based on initial dry materials). It is known that PAA is a powerful oxidizing agent and quite selective toward the lignin structure to oxidize aromat- ics in lignin generating dicarboxylic acid and their lactones [12]. Therefore, PAA loading would be reduced by a pre-pretreatment previous PAA pretreatment to partially remove lignin. Alkali has been recognized as one of the most effective agents for delignifi- cation and swelling of the fibers. Teixeira et al. found that alkaline treatments are helpful in reducing PAA requirement in pretreat- ments of sugarcane bagasse. The enzymatic hydrolysis of pretreated samples incubated at 37 ◦ C with cellulase loading of 25 FPU/g cel- lulose for 120 h was significantly increased after bagasse being 0141-0229/$ – see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.enzmictec.2008.07.011