Biodegradation of cassava starch factory residue using a combination of cellulases, xylanases and hemicellulases M.P. Divya Nair, G. Padmaja*, S.N. Moorthy Division of Crop Utilization, Central Tuber Crops Research Institute, Sreekariyam, Thiruvananthapuram 695 017, Kerala, India article info Article history: Received 11 October 2010 Received in revised form 3 December 2010 Accepted 7 December 2010 Available online 5 January 2011 Keywords: Cassava starch factory residue Biodegradation Cellulase Hemicellulase Xylanase Glucose release abstract Cassava starch factory residue (CSFR), a low cost solid byproduct of the cassava starch industry, having around 60% unextracted starch and 15% cellulose is a potential candidate for bioethanol production. As the economic feasibility depends on complete degradation of the polysaccharides to fermentable glucose, the comparative hydrolytic potential of four enzymes such as Multifect Ò XL, Optimashä XL, Optimashä BG and Accelleraseä1000 was studied. Whilst the former three enzymes exerted maximum activity at pH 5.0 and 60  C, Accellerase had optimum activity at pH 4.5 and 60  C. The enzyme cocktail, Multifect XL- Optimash XL-Accellerase (5, 15 and 20 g enzyme protein kg 1 CSFR respectively) was more effective than sequential process with the same enzyme loading. Hydrothermal treatment (HT) of CSFR for 30 min at 100  C enhanced the susceptibility to enzymatic cleavage as compared to HT for 45 and 60 min as well as autoclaving or microwave exposure. Optimash BG was the most effective on HT CSFR and approximately 704.8 g glucose was released kg 1 CSFR. The high yield of glucose indicates the potential use of hydrothermally treated CSFR as a cheap substrate for ethanol production. ª 2010 Elsevier Ltd. All rights reserved. 1. Introduction Lignocellulosic biomass such as wood or agricultural residues is a promising raw material for fuel ethanol production. Three key processes like pre-treatment to increase the digestibility of cellulose and hemicellulose by enzymes, hydrolysis of the polysaccharides to fermentable sugars and fermentation of the sugars to ethanol are involved in lignocellulosic conversion of biomass to ethanol [1]. The cost of production of ethanol from lignocellulose materials depends on the type of pre-treatment technologies needed, cost of enzymes as well as the integration of the process concepts. Soft and hardwood or agricultural residues like corn stover, sugarcane bagasse or straw contain around 22e28% lignin and around 37e45% cellulose and 8e27% hemicellulose [2e4], which necessitate rigorous pre-treatment steps to solubilize the lignin and enhance the accessibility of the substrate to cellulolytic enzymes. Environmentally benign processes like hydrothermal/steam treatment or mechanical comminution of lignocellulosic biomass are preferred over chemical pre-treatment with acids, bases or organic solvents [5e9]. The efficiency of enzymatic hydrolysis is also reported to be influenced by the degree of milling [10e12]. Cassava starch factory residue (CSFR) is a solid fibrous dry (moisture content: 12e13%) byproduct of the starch industries in India, produced at the rate of approximately 60 000 tonnes per year [13]. The dry residue has a composition of starch (56e60%), cellulose (15e18%), hemicellulose (4e5%), lignin (2e3%), protein (1.5e2.0%), pentosans (2%) and reducing sugars (0.4e0.5%) [13,14]. During the extraction of starch from wet cassava (Manihot esculenta Crantz) tubers, around 55e56% of starch goes unex- tracted due to its entrapment in the cellulose-hemicellulose matrix and CSFR causes considerable pollution problems for the * Corresponding author. Tel.: þ91 471 2598551; fax: þ91 471 2590063. E-mail address: padmajabn@yahoo.com (G. Padmaja). Available at www.sciencedirect.com http://www.elsevier.com/locate/biombioe biomass and bioenergy 35 (2011) 1211 e1218 0961-9534/$ e see front matter ª 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2010.12.009