Thermal and High-Pressure Stability of Pectinmethylesterase, Polygalacturonase, β-Galactosidase and α-Arabinofuranosidase in a Tomato Matrix: Towards the Creation of Specific Endogenous Enzyme Populations Through Processing

The thermal and pressure stability of tomato pectinmethylesterase (PME), polygalacturonase (PG), beta-galactosidase (beta-Gal), and alpha-arabinofuranosidase (alpha-Af) were investigated in situ. Enzyme inactivation by thermal and high-pressure processing (respectively 5 min at 25-95 A degrees C at 0.1 MPa and 10 min at 0.1-800 MPa at 20 A degrees C) was monitored by measuring the residual activity in crude enzyme extracts of treated tomato pur,e samples. PME was completely inactivated after a 5-min treatment at 75 A degrees C. Only 30 % of the pressure stable PME was inactivated after a treatment at 800 MPa (20 A degrees C, 10 min). A 5-min treatment at 95 A degrees C and a treatment at 550 MPa (20 A degrees C, 10 min) caused complete PG inactivation. beta-Gal and alpha-Af activities were already reduced significantly by thermal treatments at 42.5-52.5 A degrees C and 45-60 A degrees C, respectively. These enzymes were, however, rather pressure resistant: treatments at respectively 700 and 600 MPa were necessary to reduce the activity below 10 % of the initial value. Assuming that first-order, fractional conversion or biphasic inactivation models could be applied to the respective enzyme inactivation data, inactivation rate constants and their temperature or pressure dependence for the different enzymes were determined. Based on differences in process stability of the enzymes, possibilities for the creation of specific enzyme populations in tomato pur,e by selective enzyme inactivation were identified. For industrially relevant process conditions, the enzyme inactivation data obtained for tomato pur,e were shown to be transferable to intact tomato tissue.