Temperature-dependent Dielectric and Thermal Properties of Whey Protein Gel and Mashed Potato

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Chen, Jiajia; Pitchai, Krishnamoorthy; Birla, Sohan; Gonzalez, Ricardo; Jones, David; Subbiah, Jeyamkondan
Dielectric constant; Dielectric loss factor; Mashed potato; Specific heat capacity; Thermal conductivity; Whey protein gel; Biological Engineering
article description
Temperature-dependent dielectric properties (dielectric constant and dielectric loss factor) and thermal properties (thermal conductivity and specific heat capacity) of whey protein gel and mashed potato were measured from -20°C to 100°C. A dielectric properties measurement system and a multipoint temperature calibration protocol were developed. The system consists of an impedance analyzer, a high-temperature coaxial cable, a high-temperature coaxial probe, a micro-climatic chamber and a metal sample holder. Calibrations at two temperatures (25°C and 85°C) were sufficient to accurately measure the dielectric properties of foods from frozen to hot temperatures. Both dielectric constant and dielectric loss factor rapidly increased from -20°C to 0°C. Then, the dielectric constant linearly decreased from 0°C to 100°C, while the dielectric loss factor decreased first and then linearly increased. The thermal conductivity values of whey protein gel and mashed potato decreased with increasing temperature in frozen range and did not change considerably after thawing. The latent heat of fusion values of whey protein gel and mashed potato were 219.1 and 186.8 kJ•kg-1, respectively. The temperature-dependent material properties can be used in microwave heat transfer models for improving heating performance of foods in domestic microwave ovens.