Thermal resistance of tomato polygalacturonase and pectinmethylesterase at physiological pH

The kinetic parameters of heat-induced inactivation of tomato fruit pectic enzymes in a partially purified form have been calculated. Polygalacturonase I (PGI), polygalacturonase II (PGII) and pectin-methylesterase (PME) were separated by means of gel permeation chromatography and their thermoresistance in 50 mM citrate buffer, pH 4.0, 0.4 M NaCl calculated. All the enzymes showed first-order kinetics of inactivation. PGII D values ranged from 2.14 min at 64 degrees C to 0.24 min at 73 degrees C. Its z value was calculated to be 9.4 degrees C. PGI D values ranged from 15.9 min at 86 degrees C to 0.46 min at 95.4 degrees C. Its z value was calculated to be 5.6 degrees C. PME D values ranged from 7.6 min at 66.4 degrees C to 0.20 min at 74.5 degrees C. Its z value was calculated to be 5 degrees C.