Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2007
Publication Date: 5/1/2007
Citation: Kumar, P., Coronel, P., Simunovic, J., Truong, V., Sandeep, K.P. Measurement of dielectric properties of pumpable food materials under static and continuous flow conditions. Journal of Food Science. 2007. J. Food Sci. 72(4):E177-E183. Interpretive Summary: Continuous flow microwave heating is a promising alternative to conventional heating for aseptic processing of viscous food products. For microwave processing, dielectric properties play an important role in determining the interaction between the food materials and electromagnetic energy. Knowledge of dielectric properties and effects of processing conditions are essential for effective heating and safe process design. The objective of this study was to measure the dielectric properties of representative pumpable food materials by a new approach (under continuous flow conditions) and compared with the conventional approach (under static conditions) which is time consuming and may not provide the real dielectric properties of the bulk for multiphase products. The results indicated that dielectric properties measured under static and continuous flow conditions were similar for homogeneous food products such as skim milk and vegetable puree, but they were substantially different for salsa con queso which is a multiphase food product. Therefore, dielectric properties measured under continuous flow conditions can be used as a rapid method to assess the actual heating profiles of food materials, especially the multiphase products, for determining the energy input required in microwave heating systems.
Technical Abstract: Continuous flow microwave sterilization is an emerging technology which has the potential to replace the conventional heating processes for viscous and pumpable food products. Dielectric properties of pumpable food products were measured by a new approach (under continuous flow conditions) at a temperature range of 20 to 130 °C and compared with the dielectric properties measured by the conventional approach (under static conditions). The food products chosen for this study were skim milk, green pea puree, carrot puree, and salsa con queso. Second order polynomial correlations for the dependence of dielectric properties at 915 MHz of the food products on temperature were developed. Dielectric properties measured under static and continuous flow conditions were similar for homogeneous food products such as skim milk and vegetable puree, but they were substantially different for salsa con queso which is a multiphase food product. The results from this study suggest that, for a multiphase product, dielectric properties measured under continuous flow conditions should be used for designing a continuous flow microwave heating system.