Thermal inactivation of pectin methylesterase in tomato homogenate

It is well known that Pectin methylesterase (PME) is one of the most important enzymes affecting the quality of processed tomato products. A number of investigators have studied thermal inactivation of tomato PME using partially or fully purified enzymes. The aim of the present work was to calculate D and z values for thermal inactivation of PME in the homogenates among tomato cultivars growing in the U.S. and Japan, which will more closely represent actual processing conditions. D and z values for thermal inactivation of PME were determined in five U.S. and seven Nippon Del Monte (NDM) cultivars. The enzyme was comprised of both resistant and labile isozymes. At 70degreesC, the D value for labile and resistant isozymes of U.S. cultivars ranged from 5.0 to 9.5 min and 12.0 to 13.9 min, respectively. The z value of labile and resistant isozymes ranged from 4.9degreesC to 5.9degreesC and 5.1degreesC to 6.3degreesC, respectively. At 70degreesC, the D value of the labile and resistant isozymes of NDM cultivars ranged from 5.8 to 9.6 min and 10.1 to 13.9 min, respectively. The z value of labile and resistant isozymes ranged from 5.9 to 6.8degreesC and 6.2degreesC to 7.6degreesC, respectively. D value of cold-break cultivar did not essentially differ from that of hot-break cultivar. D values determined in homogenate were higher than those reported for purified PME performed in buffer solutions. This suggests that controlling thermal processing is important in the production of tomato paste or diced tomatoes.