High-pressure and temperature effects on enzyme inactivation in tomato puree

A study was made of the effect of high hydrostatic pressure treatment (50-500 MPa) combined with heat treatment (20-60 degrees C) on peroxidase (POD), polyphenol oxidase (PPO), and pectin methylesterase (PME) activities of tomato puree. Assays were carried out on fresh made tomato puree, and a 15 min treatment time was selected. Pressurization/depressurization treatments caused a continuous denaturation of soluble proteins at room temperature (20 degrees C). Also, ultrahigh hydrostatic pressure (UHP)/mild heat treatments produced a significant reduction (32.5%) of PME activity when a combination of 150 MPa/30 degrees C treatment was employed, while some activation was observed for treatments carried out at 335-500 MPa and different temperatures. A reduction of POD activity (25%) was obtained in tomato purees treated at 350 MPa/20 degrees C, but a combination of higher pressures and mild temperatures (30-60 degrees C) produced an enhancement of this activity. PPO activity did not show any significant change due to UHP/mild-temperature treatments in tomato product. Only a combination of 200 MPa/20 degrees C seemed to produce a significant loss (10%) in PPO activity.