Abstract
The effects of yeast extract (X1), NH4NO3 (X2), peptone (X3), urea (X4), CMC (X5), Tween 20 (X6), MgSO4 (X7), and CaCO3 (X8) on production of xylanase from Cellulosimicrobium cellulans CKMX1 were optimized by statistical analysis using response surface methodology (RSM). The RSM was used to optimize xylanase production by implementing the Central composite design. Statistical analysis of the results showed that the linear, interaction and quadric terms of these variables had significant effects. However, only the linear effect of X4, X5, interaction effect of X1X7, X1X8, X2X3, X2X8, X3X6, X3X8, X4X6, X4X7, X5X7, X5X8 and quadratic effect of X32, X52 and X72 found to be insignificant terms in the quadratic model and had no response at significant level. The minimum and maximum xylanase production obtained was 331.50 U/g DBP and 1027.65 U/g DBP, respectively. The highest xylanase activity was obtained from Run No. 30, which consisted of yeast extract (X1), 1.00 g (%); NH4NO3 (X2), 0.20 g (%); peptone (X3), 1.00 g (%); urea (X4), 10 mg (%); CMC (X5), 1.00 g (%); Tween 20 (X6), 0.02 mL (%); CaCO3 (X7), 0.50 g (%) and MgSO4 (X8), 9.0 g (%). The optimization resulted in 3.1-fold increase of xylanase production, compared with the lowest xylanase production of 331.50 U/g DBP after 72 h of incubation in stationary flask experiment. Application of cellulase-free xylanase in pulp biobleaching from C. cellulans CKMX1 under C–EP–D sequence has been shown to bring about a 12.5 % reduction of chlorine, decrease of 0.8 kappa points (40 %), and gain in brightness was 1.42 % ISO points in 0.5 % enzyme treated pulp as compared to control.
Highlights
Xylan is the major hemicellulosic constituent of hard and soft wood and is the most abundant renewable polysaccharide after cellulose
Application of cellulase-free xylanase in pulp biobleaching from C. cellulans CKMX1 under C–EP–D sequence has been shown to bring about a 12.5 % reduction of chlorine, decrease of 0.8 kappa points (40 %), and gain in brightness was 1.42 % ISO points in 0.5 % enzyme treated pulp as compared to control
For response surface methodology (RSM) based on the central composite design (CCD), used for the optimization of independent variables for the xylanase production, 51 experimental runs with different combinations of eight factors were carried out
Summary
Xylan is the major hemicellulosic constituent of hard and soft wood and is the most abundant renewable polysaccharide after cellulose. This complex heteropolysaccharide consists of a main chain of 1,4-b-Dxylose monomers and short chain branches consisting of Oacetyl, a-L-arabinofuranosyl and a-D-glucuronyl residues. The commercial application of xylanase in various industrial processes has had limited success due to various factors. These include inaccessibility of substrate to xylanase enzymes because of physical limitations, the limited hydrolysis of xylans due to their branched nature, thermal instability, narrow pH range, end product inhibition and cost of enzyme production. The last two problems can be overcome to some extent by the use of cheap substrates and by employing the process of solid-state fermentation (SSF)
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