Purification and characterization of β-mannanase from Aspergillus terreus and its applicability in depolymerization of mannans and saccharification of lignocellulosic biomass

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 Km and Vmax 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.