Statistical screening and optimization of process variables for xylanase production utilizing alkali-pretreated rice hus

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ORIGINAL ARTICLE

Statistical screening and optimization of process variables for xylanase production utilizing alkali-pretreated rice husk Anita Singh & Manju & Anurag Yadav & Narsi R. Bishnoi

Received: 23 January 2012 / Accepted: 27 April 2012 / Published online: 26 May 2012 # Springer-Verlag and the University of Milan 2012

Abstract With the objective of the production of xylanase, local raw material (rice husk) and the indigenous isolate, Aspergillus niger ITCC 7678, were studied. Optimization of the cultivation system for enhancing xylanase production was studied via submerged fermentation. Statistical procedures were employed to study the effect of process variables, such as alkali-pretreated rice husk (as carbon source), NaNO3 (as nitrogen source), KH2PO4, KCl, Tween 80 (as surfactant), MgSO4, FeSO4·7H2O, pH, particle size, agitation, and temperature, on xylanase production by A. niger. The effect and significance of the variables was studied using Plackett–Burman (PBD) and central composite statistical design (CCD). It was found that alkali pretreated rice husk (weight/volume), pH, temperature, and NaNO3 significantly influence xylanase production. So, these four factors were further optimized by CCD, and it was found that maximum xylanase activity of 10.9 IU/ml was observed at (6.5 % w/v) rice husk, pH (5.5), temperature (32.5 °C), and NaNO3 (0.35 % w/v) concentration. Under optimum conditions, xylanase production was also studied at the bioreactor level and showed 12.8 % enhanced xylanase activity. Keyword Aspergillus niger . Plackett Burman . Xylanase . Lignocellulosic biomass A. Singh : Manju : A. Yadav : N. R. Bishnoi (*) Department of Environmental Science and Engineering, Guru Jambheshwar University of Science and Technology, Hisar 125001, Haryana, India e-mail: [email protected] e-mail: [email protected]

Introduction Lignocelluloses are mainly secondary plant cell-wall materials which consist of lignin, cellulose, and hemicellulose (Singh et al. 2010). Xylan is a major hemicellulose found in wood and accounts for 20–35 % of the total dry weight of hardwood and perennial plants, and is considered, with cellulose and chitin, as being among the most abundant polysaccharides in nature. It is composed of a linear backbone of 1,4-β-linked-Dxylopyranosyl units that often has side chains of Oacetyl, arabinosyl, and methylglucuronosyl substituents (Blanco et al. 1997; Maheshwari et al. 2000). Endo-β-1,4xylanase (1,4-β-D-xylan xylanohydrolase, EC 3.2.1.8) is the main enzyme responsible for the cleavage of the linkages within the xylan backbone (Belfaquih et al. 2002). Filamentous fungi are industrially important producers of this enzyme due to extracellular release of xylanases, higher yields compared to yeast and bacteria, and production of several auxiliary enzymes that are necessary for debranching of the substituted xylans (Haltrich et al. 1996). Xylanases show great potential for industrial applications mainly for the bioconversion of lignocelluloses to sugar, ethanol, and other useful substances