Enzyme and Microbial Technology, Vol.101, 17-23, 2017
Characterization and thermal inactivation kinetics of highly thermostable ramie leaf beta-amylase
We characterized ramie leaf beta-amylase, and determined its thermostability and kinetic parameters. The enzyme was purified 53-fold using ammonium sulfate fractionation (40-60% saturation), anion exchange chromatography on DEAE-cellulose and gel permeation chromatography on Superdex-200. The purified enzyme was identified as beta-amylase with molecular mass of 42 kD. The enzyme displayed K-m and k(cat) values for soluble potato starch of 1.1 mg/mL and 7.8 s(-1), respectively. The enzyme had a temperature optimum of 65 degrees C, and its activity at 70 degrees C was 92% of that at the optimal temperature after a 15-min incubation. Furthermore, enzyme activity was stable during treatment at 55 degrees C for 60 min but was inactivated rapidly at >75 degrees C. This thermal behavior indicates that ramie leaf beta-amylase has excellent intermediate temperature-stable enzyme properties for the baking and bio-industries. Inactivation of the enzyme followed first-order kinetics in the range of 55-80 degrees C. The enthalpy change of thermal inactivation (Delta H-double dagger), Delta G(double dagger), and Delta S-double dagger were 237.2 kJ/mol, 107.7 kJ/mol, and 0.39 kJ/mol K at 333 K, respectively. The D-value at 65 degrees C (= 110 min) and the z-value (=9.4 degrees C) are given for food processing. (C) 2017 Elsevier Inc. All rights reserved.