Characterization and Thermal Inactivation Kinetics of Highly Thermostable Ramie Leaf β-amylase

Abstract We characterized ramie leaf β-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 β-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 °C, and its activity at 70 °C was 92% of that at the optimal temperature after a 15-min incubation. Furthermore, enzyme activity was stable during treatment at 55 °C for 60 min but was inactivated rapidly at >75 °C. This thermal behavior indicates that ramie leaf β-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 °C. The enthalpy change of thermal inactivation ( ΔH ‡ ), ΔG ‡ , and ΔS ‡ were 237.2 kJ/mol, 107.7 kJ/mol, and 0.39 kJ/mol K at 333 K, respectively. The D-value at 65 °C (= 110 min) and the z-value (= 9.4 °C) are given for food processing.