THERMAL INACTIVATION OF PECTIN METHYLESTERASE IN TOMATO PUREE - IMPLICATIONS ON CLOUD STABILITY

The thermal behaviour of pectin methylesterase (PME, EC. 3.1.1.11) in five new tomato cultivars used for juices and tomato products was anal ysed. Enzyme inactivation induced by heat was followed by measuring th e activity as a function of temperature. The thermal behaviour of PME activity in five tomato varieties was described by sigmoidal thermal d enaturation curves. The data analysis, performed assuming a two state equilibrium model, showed that only one of the five tomato varieties r etained PME activity This observation could explain the cloud loss sho wn by some tomato products during storage. From the thermal transition curves, the D-T, Z and F/D parameters, usually employed for the evalu ation of stabilization thermal processes, were calculated at various p H values.