I. Verlent

Comparative study of the inactivation kinetics of pectinmethylesterase in tomato juice and purified form.

Pectinmethylesterase (PME) extracted from tomato fruit was purified by affinity chromatography. A single peak of PME activity was observed, presenting a molar mass of 33.6 kDa, an isoelectric point higher than 9.3, and an optimal temperature and pH for activity of 55 °C and 8.0, respectively. The processing stability of purified tomato PME in buffer solution was compared to PME stability in tomato juice. In both media, thermal inactivation of PME presented first‐order inactivation kinetics, PME in tomato juice being more heat‐labile than purified PME. Regarding high‐pressure treatment, tomato PME showed to be very pressure‐resistant, revealing an outspoken antagonistic effect of temperature and pressure. To avoid cloud loss in tomato juice, a time‐temperature treatment of 1 min at 76.5 °C was calculated in order to have a residual PME activity of 1 × 10−4U/mL.

Inactivation kinetics of polygalacturonase in tomato juice

a ¸ ´´ ˜ ´ Abstract The inactivation kinetics of polygalacturonase (PG) in tomato juice was studied during thermal and high-pressureythermal processing. In the temperature range of 55-70 8C the thermal inactivation of polygalacturonase in tomato juice followed a fractional conversion model, with a thermostable fraction of approximately 14%. Under conditions of combined high-pressurey thermal processing, 200-550 MPay5-50 8C, PG inactivation presented first order kinetics. A mathematical model to describe the inactivation rate constant as a function of pressure and temperature was formulated. Industrial relevance: Polygalacturonase is responsible for the decrease of viscosity in tomato-based products. However, little research on thermal and high pressure ythermal inactivation kinetics of tomato Polygalacturonase has been reported. This research clearly shows that it is possible to selectively inactivate PG by high pressureythermal processing without applying high temperatures. This leads to tomato-based products with improved functional properties while other quality attributes (color, flavor, nutritional value ) are maintained. 2002 Elsevier Science Ltd. All rights reserved.

Strawberry Pectin Methylesterase (PME): Purification, Characterization, Thermal and High-Pressure Inactivation

Pectin methylesterase (PME) was extracted from strawberries ( Fragaria ananassa, cv Elsanta) and purified by affinity chromatography on a CNBr‐Sepharose 4B‐PME‐inhibitor column. A single protein and PME activity peak was obtained. A biochemical characterization in terms of molecular mass, pI, and kinetic parameters of strawberry PME was performed. In a second step, the thermal and high‐pressure stability of the enzyme was studied. Isothermal and combined isothermal‐isobaric inactivation of purified strawberry PME could be described by a fractional‐conversion model. Purified strawberry PME is much more stable toward high‐pressure treatments in comparison to those from oranges and bananas.

Effect of Temperature and High Pressure on the Activity and Mode of Action of Fungal Pectin Methyl Esterase

Pectin was de‐esterified with purified recombinant Aspergillus aculeatus pectin methyl esterase (PME) during isothermal‐isobaric treatments. By measuring the release of methanol as a function of treatment time, the rate of enzymatic pectin conversion was determined. Elevated temperature and pressure were found to stimulate PME activity. The highest rate of PME‐catalyzed pectin de‐esterification was obtained when combining pressures in the range 200–300 MPa with temperatures in the range 50–55 °C. The mode of pectin de‐esterification was investigated by characterizing the pectin reaction products by enzymatic fingerprinting. No significant effect of increasing pressure (300 MPa) and/or temperature (50 °C) on the mode of pectin conversion was detected.

Kinetic Information on Thermal and High Pressure-Temperature Inactivation of Pectinesterases

Several key effects and advantages of high hydrostatic pressure have resulted in the current interest of the food industry to use this novel technology in food processing or preservation, replacing or complementing thermal processing. In this context, the current paper focuses on kinetic studies of the activity and stability of pectinesterase (PE) from oranges and tomatoes during thermal and high pressure processing. In addition, the influence of intrinsic product properties such as pH and Ca2+-ions on the processing stability of PE is quantified.