Abstract
Aspergillus terreus FBCC 1369 was grown in solid-state culture under statistically optimized conditions. β-Mannanase was purified to apparent homogeneity by ultrafiltration, anion exchange and gel filtration chromatography. A purification factor of 10.3-fold was achieved, with the purified enzyme exhibiting specific activity of 53 U/mg protein. The purified β-mannanase was optimally active at pH 7.0 and 70 °C and displayed stability over a broad pH range of 4.0–8.0 and a 30 min half-life at 80 °C. The molecular weight of β-mannanase was calculated as ~49 kDa by SDS-PAGE. The enzyme exhibited K m and V max values of 5.9 mg/ml and 39.42 µmol/ml/min, respectively. β-Mannanase activity was stimulated by β-mercaptoethanol and strongly inhibited by Hg2+. The β-Mannanase did not hydrolyze mannobiose and mannotriose, but only mannotetraose liberating mannose and mannotriose. This indicated that at least four mannose residues were required for catalytic activity. Oligosaccharide with a degree of polymerization (DP) three was the predominant product in the case of locust bean gum (16.5 %) and guar gum (15.8 %) hydrolysis. However, the enzyme liberated DP4 oligosaccharide (24 %) exclusively from konjac gum. This property can be exploited in oligosaccharides production with DP 3–4. β-Mannanase hydrolyzed pretreated lignocelluloses and liberated reducing sugars (% theoretical yield) from copra meal (30 %). This property is an important factor for the bioconversion of the biomass.Electronic supplementary materialThe online version of this article (doi:10.1007/s13205-016-0454-2) contains supplementary material, which is available to authorized users.
Highlights
In plant cell walls, hemicelluloses are the second most abundant carbohydrates after cellulose
Among the six substrates examined for the production of bmannanase in SSF, copra meal was observed to be the best supporting 59 U/gds b-mannanase (Supplementary Table 2)
Copra meal was used for further optimization
Summary
Hemicelluloses are the second most abundant carbohydrates after cellulose. Mannans are the second largest group of hemicelluloses after xylan, which appear predominantly in softwoods of gymnosperms and form a minor component of hardwoods (Puls and Schuseil 1993). These are composed of b-linked mannose sugar-based backbones with variable degrees of side substitutions. These polysaccharides are renewable resources and their enzymatic conversion is of great interest in the field of lignocellulose biotechnology (Soni and Kango 2013). The breakdown of the main chain of mannan is accomplished with the action of b-mannanase (1,4-bmannan mannohydrolases EC 3.2.1.78), which releases manno-oligosaccharides. Enzymes that actively participate in mannan hydrolysis include b-mannanase (1,4-b-D-mannan mannohydrolase, EC 3.2.1.78), b-mannosidase (1,4-bD-mannopyranoside hydrolase, EC 3.2.1.25), b-glucosidase (1,4-b-D-glucoside glucohydrolase, EC 3.2.1.21) and
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