There is currently no recognised equation, or set of equations, that can be used to adequately describe moisture dependant dielectrics. This study addresses this issue so that moisture dependant dielectric properties can be directly input into drying models, where the microwave or radio frequency source is always limited to a single frequency. This was achieved by adapting water activity equations to describe the moisture dependant behaviour of the loss factor and the dielectric constant of hygroscopic inhomogeneous materials at microwave and radio frequencies. These equations were fitted to thirty moisture dependant loss factor and dielectric constant data sets. The adapted water activity equations proved to be very effective at describing dielectric behaviour, with the best equation fits to the thirty moisture dependant dielectric data sets having an average Mean Relative Error of 2.99%. The suitability of the equations are discussed, and specific equations are recommended for fitting to different types of moisture dependant dielectric response.

In this study, we found that treatment with cold plasma influenced the wetting properties of soy protein isolate and milk protein concentrate powders. Cold plasma treatment significantly decreased the apparent contact angle of the powders, indicating hydrophilization of the powders. Cold radiofrequency low-pressure plasma treatment had a larger effect on powder wettability than corona atmospheric plasma discharge. In addition, cold plasma treatment had a more noticeable effect on the wettability of the hydrophobic milk protein concentrate than on the inherently hydrophilic soy protein isolate. Both the soy protein isolate and milk protein concentrate demonstrated zero hydrophobic recovery over time. Scanning electron microscopy showed that cold air plasma treatment of food powders caused minor surface oxidation, though these changes were not observed using FTIR spectroscopy. We suggest that cold plasma treatment has important implications for the production of stabilizer-free food suspensions.