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.