Effects of reduced malto-oligosaccharides on the thermal stability of pullulanase from Bacillus acidopullulyticus.

We investigated the effects of the reduced malto-oligosaccharides, D-glucitol (G1-OH), maltitol (G2-OH), maltotriitol (G3-OH), maltotetraitol (G4-OH), and maltopentaitol (G5-OH) on the thermal stability of Bacillus acidopullulyticus pullulanase (EC 3.2.1.41). The thermal stability depended on the concentration of D-glucitol; after heat treatment for 90 min at 60 degrees in the presence of 0.56, 0.28, 0.14, or 0M G1-OH, the residual activity was 100, 80, 32, and 10% of the control, respectively. Stability increased with the number of glucosyl residues in the alditols added; the effects of G3-OH, G4-OH, and G5-OH on stability were remarkable. Addition of 30% G2-OH, G3-OH, and G4-OH also contributed to the thermal stability of the pullulanase immobilized onto chitosan beads treated with glutaraldehyde. A high concentration of G2-OH stabilized other debranching amylases, Klebsiella pneumoniae pullulanse, Bacillus sectorramus pullulanase, and Pseudomonas amyloderamosa isoamylase (EC 3.2.1.68) under heat treatment for 48 h at 60 degrees, as well as the pullullanase of B. acidopullulyticus.