Modification of guar galactomannan with the aid of Aspergillus niger pectinase

Pectinase from Aspergillus niger associated with polygalacturonase activity, caused considerable debranching-depolymerization of guar galactomannan. Zymogram analysis further confirmed the action of pectinase on the latter. Optimum activity occurred at pH 5.0 and 50 °C and the reaction obeyed Michaelis-Menten kinetics with Km and Vmax values of 3.72 mg mL−1 and 1.852 mmoles min−1 mg−1. Viscometry, GPC and HPLC analyses of the native guar galactomannan showed a molecular weight (Mw) of ∼240 kDa with a galactose:mannose (G:M) ratio of 1:1.6, as revealed by GLC analysis, whereas, after enzymatic catalysis for 60 min, the major resultant product had a Mw of ∼70 kDa with a G:M ratio of 1:2.8, respectively. The latter had a solubility of ∼98% in water at ambient temperature (within 30 min) compared to ∼60% for native galactomannan. IR spectral analysis revealed differences in the conformation of enzyme catalyzed guar galactomannan. The latter showed better gelling property with xanthan gum compared to native galactomannan. Use of non-specific pectinase for debranching-depolymerization of guar galactomannan is of commercial interest as modified galactomannans find multiple applications as functional food ingredients.