Inactivation kinetics of pectin methylesterase and cloud retention in sonicated orange juice

The effect of sonication on pectin methylesterase (PME) activity and cloud stability of orange juice was studied. Ultrasonic acoustic energy density (AED) levels of 0.42, 0.47, 0.61, 0.79 and 1.05 W/mL and treatment times of 0 (Control), 2, 4, 6, 8 and 10 min were investigated. The highest PME inactivation level observed was 62% for sonication at the highest AED level and treatment time. A fraction conversion model adequately described the PME inactivation compared to first order or polynomial models. A significant change in particle size distribution was observed in sonicated samples due to cavitational effects. These results indicate that the cloud stability of sonicated orange juice depends not only on PME inactivation but also on particle size reduction. Industrial relevance: Power ultrasound is a non thermal pasteurisation method that has been identified to meet the US FDA requirement for a 5 log reduction in E coli pertinent to fruit juices. Apart from microbial inactivation, cloud stability is a critical orange juice quality parameter influencing product shelf life and consumer acceptance. This work demonstrates that sonication at low AED levels and temperatures can be employed to achieve the desired cloud stability. (C) 2008 Elsevier Ltd. All rights reserved.