Process alternatives
A number of process conditions were selected for their commercial feasibility. Since PME is attached to the cell walls of the juice sacs, total PME activity increases with the pulp level. This means that commercial juices with high pulp levels pose a special challenge to achieving sufficient PME inactiva- tion. For these experiments orange juice with 8.5% added unpasteurized or pasteurized pulp was used. This pulp level is found in commercial not-from-concentrate orange juices with high pulp levels.
Processing of juice with unpasteurized pulp at 800 MPa resulted in almost instantaneous PME inactivation with a re- sidual activity of 6.4% (Table 1). This alternative required the shortest processing time, but high pressures above 600 MPa may be commercially undesirable as more expensive equip- ment is required to continuously operate at these pressures. Processing at 600 MPa or 500 MPa in combination with mild heat required longer processing times of at least 5 mins. Irwe and Olsson (1994) explored combinations of pressure (400 and 600 MPa) and process temperature (20 to 60