| Dielectric heating of biomaterials was investigated from the physical, chemical, and electrical properties perspectives. Primary focus was on the electrical properties, especially dielectric properties. The dielectric constant (epsilon') and loss factor (epsilon'') were studied at the molecular level of the materials' composition; primarily water, carbohydrates, and proteins. Effects of components were investigated individually and in combination in aqueous media. Measurements were conducted using an open-ended coaxial probe connected to an impedance analyzer.; Properties of food carbohydrates (starch, sucrose, glucose, and fructose) were investigated over the frequency range 10--1800 MHz at 20--60 °C, and to 100 °C for starch solutions. The influences of electrical field frequency (f), temperature (T), and concentration (C) on the dielectric constant and loss factor were thoroughly examined and theoretically interpreted. The dielectric constant's response to frequency was fairly independent from 10 to 1000 MHz, but began a significant and progressive decline at frequencies beyond 1000 MHz.; Influences of protein solutions (ovalbumin, bovine serum albumin, beta-lactoglobulin, and lysozyme) were investigated in aqueous media at 450 selected frequencies between 5 MHz and 1800 MHz. All examined proteins exhibited similar dielectric dispersions for the selected concentrations (i.e., 5, 10, 20, 30, 40 and 50 mg/g) and results agreed fairly well with previously published data. Delta-dispersions (deltas) between beta and gamma-dispersions for protein solutions were observed, although at higher relaxation frequencies than those previously published. Contribution of individual proteins to the dielectric loss, and consequently thermal generation in dielectrically heated biomaterials, was investigated and found to have greater effect at low frequencies, especially at 27 MHz. Theoretical calculation of the local dielectric constant (epsilon') of individual proteins from their amino acid composition resulted in a mean value of 2.70. A derived mixture equation provided results that agreed with experimental data at frequencies close to the industrial microwave frequency (915 MHz).; Dielectric measurements of protein-sugar aqueous mixtures were also conducted in the 10--1800 MHz frequency range. Rayleigh, Bottcher, and Berentsveig mixture models were utilized to predict the mixtures' dielectric constants. Calculated values agreed with the experimental data, except for the three-component mixture result obtained using the Rayleigh model. |
