Nonspecific Activity of Bacillus acidopullulyticus Pullulanase on Debranching of Guar Galactomannan

Pullulanase (EC 3.2.1.41) from Bacillus acidopullulyticus could preferentially remove galactose residues from guar galactomannan (GG), a heteropolymer consisting of polymannan backbone with alternating galactose as single-residue side-chain stubs. The enzyme showed maximum activity at pH 4.5 and 45 °C and exhibited Michaelis−Menten kinetics with a Km and Vmax of 6.0 mg mL−1 and 1820 nmol min−1 mg−1, respectively. The native and modified GG had a viscosity of 4800 and 3800 cps, respectively. The molecular mass of the enzyme-treated GG varied between 152 ± 0.5 kDa, and its GLC analysis revealed a significant change in galactose−mannose content of 1:3.8, respectively, similar to that of locust bean gum (LBG). FTIR and solid-state CP-MASS 13C NMR analyses indicated subtle changes in the conformation of modified GG because of the removal of galactose residues. Gel-strength measurements with κ-carrageenan showed an improvement in the gelling behavior, similar to that shown by LBG. Debranching of GG by pullulanase is an alternative and inexpensive route to produce modified GG with enhanced functional properties, as a cost-effective replacement for LBG.