MICROWAVE HEATING OF LOW-LOSS DIELECTRIC FOOD PRODUCTS

In the food industry, production of powdered materials enables to extend the shelf life of foods while preserving their intrinsic qualities. Moreover, in the case of high protein dairy powders, the application of a high temperature treatment (i.e. T ≥ 80°C) may modify proteins structure and thus their potential functionalities for further processing or incorporation within other food matrixes. This solution is particularly adapted in the context of a Clean Label approach where significant reductions of additives and other controversial ingredients are expected. In this study, a microwave heat treatment is applied to a whey proteins isolate (WPI) powder in a dry state. The thermophysical properties of the WPI powder (density, specific heat and thermal conductivity) were measured or taken from literature. A dielectric characterization using a resonant cavity perturbation technique is also presented and the measurements confirmed the low dielectric loss factor of the sample. A 3D numerical model, which includes a single mode microwave cavity working at 2.45 GHz, is also developed to understand the microwave interactions with the powdered food. Simulation results are discussed on the one hand in terms of electromagnetic field propagation within the rectangular waveguide and on the other hand by considering the temperature distribution within the powdered food. The model is experimentally validated with a pilot-scaled microwave equipment (2.45 GHz solid-state microwave emitter, impedance tuner and optical fibers probes). This study will give significant guidelines for the microwave heating optimization of low-loss dielectric products such as powdered food materials