Changes in purified tomato pectinmethylesterase activity during thermal and high pressure treatment

The enzymatic reaction of purified tomato pectinmethylesterase on pectin was investigated during a combined high pressure/temperature treatment (0.1-600 MPa/20-65 °C) at pH 8.0 and pH 4.4. The optimal temperature for tomato pectinmethylesterase activity at atmospheric pressure is situated around 45 °C at pH 8.0, and around 35 °C at pH 4.4. At both pH 8.0 and pH 4.4, the optimal temperature shifted to higher values at elevated pressure compared with atmospheric pressure. At both pH values, the catalytic activity of tomato pectinmethylesterase was higher at elevated pressure than at atmospheric pressure, creating possibilities for rheology improvements by pressure processing. Maximal tomato pectinmethylesterase activity in the pressuretemperature domain investigated was observed at 55 °C and 300 MPa for pH 8.0 and at 57 °C and 450 MPa for pH 4.4. However, under all pressure-temperature conditions tested the catalytic activity of tomato pectinmethylesterase at pH 4.4 was much lower than at pH 8.0. The chemical de-esterification of pectin at pH 8.0 was accelerated by increasing pressure and temperature, whereas no chemical deesterification of pectin was observed at pH 4.4.