Purification and Characterization of Endo-β-1,4 Mannanase from Aspergillus niger gr for Application in Food Processing Industry

A thermostable extracellular beta-mannanase from the culture supernatant of a fungus Aspergillus niger gr was purified to homogeneity. SDS-PAGE of the purified enzyme showed a single protein band of molecular mass 66 kDa. The beta-mannanase exhibited optimum catalytic activity at pH 5.5 and 55 degrees C. It was thermostable at 55 degrees C, and retained 50% activity after 6 h at 55 degrees C. The enzyme was stable at a pH. range of 3.0 to 7.0. The metal ions Hg2+, Cu2+, and Ag2+ inhibited complete enzyme activity. The inhibitors tested, EDTA, PMSF, and 1,10-phenanthroline, did not inhibit the enzyme activity. N-Bromosuccinimide completely inhibited enzyme activity. The relative substrate specificity of enzyme towards the various mannans is in the order of locust bean gum > guar gum > copra mannan, with K-m of 0.11, 0.28, and 0.33 mg/ml, respectively. Since the enzyme is active over a wide range of pH and temperature, it could rind potential use in the food-processing industry.