Evaluation of processing qualities of tomato juice induced by thermal and pressure processing

Effects of processing conditions including hot-break processing (92 degrees C for 2 min), cold-break processing (60 degrees C for 2 min) and hydrostatic pressure treatments (100-500 MPa) at different temperatures (4, 25 and 50 degrees C) for 10 min on quality aspects of tomato juice were investigated. Both hot- and cold-break processing induced significant changes in color, viscosity and radical-scavenging capacity of tomato juice compared with control (fresh tomato juice); moreover, hot-break processing induced a specific range of reduction of pectin methylesterase (PME) and polygalacturonase (PG) activities. Pressure treatments at and below 200 MPa at 4 and 25 degrees C maintained the color, extractable total carotenoids and lycopene, and radical-scavenging capacity; further, those at 500 MPa at 4 and 25 degrees C improved all the quality attributes the most except inactivation of PME in this study. The residual activity of PME showed the lowest after treating by 200 MPa at 25 degrees C however, the PME activity was enhanced by treatments at 300-500 MPa and various temperatures. The residual activity of PG decreased gradually to 72% with pressure elevated from 100 to 400 MPa at 4 and 25 degrees C, further, that declined quickly to 10% after 500 MPa treatments. This research clearly shows that it is possible to selectively produce good tomato juice products by high pressure processing at ambient temperature. (C) 2007 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.