Purification, properties and heat inactivation of pectin methylesterase from apple (cv Golden Delicious)

Pectin methylesterase from apple (cv Golden Delicious) was extracted and purified by affinity chromatography on a CNBr-Sepharose®-PMEI column. A single pectin methylesterase peak was observed. Isoelectric points were higher than 9. Kinetic parameters of the enzyme were determined as Km = 0.098 mg ml−1 and Vmax = 3.86 µmol min−1 ml−1 of enzyme. The optimum pH of the enzyme was above 7.5 and its optimum temperature was 63 °C. The purified PME required the presence of NaCl for optimum activity, and the sodium chloride optimum concentration increased with decreasing pH (from 0.13 M at pH 7 to 0.75 M at pH 4). The heat stability of purified PME was investigated without and with glycerol (50%), and thermal resistance parameters (D and Z values) were calculated showing that glycerol improved the heat resistance of apple PME.