Thermal and high-pressure stability of purified pectin methylesterase from plums (Prunus domestica)

Pectin methylesterase (PME) from greengage plums (Prunus domestica) has been extracted and purified using affinity chromatography. Only one band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis was obtained, with an estimated molecular weight of 31 kDa. On isoelectric focusing electrophoresis, two bands with neutral isoelectric points (6.8 and 7.0) were detected. The optimal pH and temperature for plum PME activity were 7.5 and 65C, respectively. A study of purified plum PME thermostability was performed at pH 7.5 and 4.0, indicating a higher thermostability at pH 7.5 than at pH 4.0. A biphasic inactivation behavior was observed for thermal treatments (54-70C), whereas its pressure inactivation could be described by a first-order kinetic model in a pressure range of 650-800 MPa at 25C. Purified plum PME was found to be relatively stable to thermal and pressure (</=600 MPa) treatments, compared to PME from other fruits

Process stability of Capsicum annuum pectin methylesterase in model systems, pepper puree and intact pepper tissue

Process stability studies towards temperature and/or pressure on pepper pectin methylesterase (PME) were carried out in different systems (purified form, crude extract, pepper pieces and puree) at pH 5.6. Within the temperature range studied (22–80 °C, 5 min), pepper PME in pure form and crude extract was gradually inactivated showing a biphasic inactivation behaviour, indicating the presence of isoenzymes of different thermostability. Pepper samples heated for 15 min showed a maximum of residual PME activity around 55 °C. Isothermal inactivation of pepper PME in purified form and crude extract at pH 5.6 could be described by a biphasic inactivation model for the temperature range studied (62–76 °C). A stable behaviour towards high-pressure/temperature treatments (400–800 MPa/25–60 °C) was observed for crude extract and purified pepper PME. PME in pepper puree samples revealed to be very pressure stable. Mild temperatures combined with pressure treatments seem to increase the extractability from PME in pepper tissue, probably due to the effect on the cell structure