Kinetics determine effective process conditions for orange juice cold pasteurization.

Maintaining the quality of fresh orange juice is highly dependent on the activity of pectinolytic enzymes and the growth of spoilage microorganisms.

Greek scientists investigated the inactivation kinetics of indigenous pectin methylesterase (PME) and of two pressure-resistant species of spoilage lactic acid bacteria (LAB), L. plantarum and L. brevis, in freshly squeezed Valencia orange juice. The kinetics were examined under high hydrostatic pressure, at from 100 MPa to 500 MPa, and at moderate temperatures, ranging from 20 C to 40 C.

PME inactivation followed first-order kinetics with a residual PME activity of 15% at all pressure-temperature combinations used by the researchers. The values for activation energy and activation volume were estimated at each pressure and at each temperature, respectively. Values of 90 kJ per mol and 30 mL per mol at a reference pressure of 300 MPa and reference temperature of 35 C were determined, respectively. The corresponding zT and zP values of LAB inactivation were also estimated at all conditions tested. These values indicate thermoelectric efficiency.

Values of 19.5 C and 95 MPa at a reference pressure of 300 MPa and a reference temperature of 30 C were found, respectively, for L. plantarum. The corresponding values for L. brevis were 40 C and 82 MPa, respectively, at the same reference conditions.

The investigators found pressure and temperature to act synergistically both for PME and LAB inactivation. The PME and LAB inactivation rate constants were expressed as functions of the temperature and pressure process conditions. These functions make it possible to determine the pressure- temperature conditions that achieve the target enzyme and microbial inactivation at a selected processing time. The scientists indicate that process conditions of 350 MPa at 35 C for 2 minutes are effective for Valencia orange juice cold pasteurization.

Further information. Petros S. Taoukis, Laboratory of Food Chemistry and Technology, School of Chemical Engineering, National Technical University of Athens, 5 Iroon Polytechniou St., Athens 15780, Greece; phone: [phone]; fax: [phone]; email: [e-mail].