Prediction of Dielectric Properties in Solid Foods of High Moisture Content at Ultrahigh and Microwave Frequencies

Abstract

Recent studies have shown that dielectric properties of raw potato can be predicted over the range of 300–3000 Mhz and 5–65°C by a noninteractive Distributive model derived from lumped circuit analysis by a two‐phase approximation which treats the potato as a binary system consisting of an inert solid phase and an active liquid phase. Dielectric behavior was seen to result primarily from water and ion activities of aqueous regions but subject to appreciable modification by a mechanism of volume exclusion due to effects of colloidal solids. Cell‐free and whole potato extract measurements showed cation binding and complexing effects, resulting in considerably lower effective salts concentrations than implied by ash content. In addition, intracellular cation and biochemical constituent levels, were significantly higher than extracellular levels. However, dielectric behavior of aqueous regions of the potato appeared to be based on bulk average fluid properties subject to displacement by colloidal solids. Low‐frequency measurements of raw potato showed other regions of relaxation and conductivity effects rather than free water and bulk conductivity at low frequencies. But these appeared not to contribute to high‐frequency dielectric response of the potato since observed relaxations were of small magnitude or occurred at frequencies well below the ultrahigh and microwave regions, suggesting that surface properties of solid foods may not be of much significance at high frequencies. Preliminary analysis of solid food measurements by other workers suggests the feasibility of modelling solid food behavior by two‐phase approximations of Distributive, Maxwell or Rayleigh model behavior based on physical‐chemical properties. For example, raw beef measurements were predicted closely by a two‐phase model in Rayleigh form, suggesting modelling characteristics similar to the potato but with specific model behavior due to differencesin biological structure of beef and potato. A general physical‐chemical model is proposed for high‐frequency dielectric behavior of solid foods based on observed mechanisms of interaction between water and the biochemical constituents of foods.

A Simple Procedure to Determine Complex Permittivity of Moist Materials Using Standard Commercial Coaxial Sensor

“…The loss factor, , decreases at low frequency, but increases again at 2 GHz. This behavior is influenced by ionic conductivity at lower frequencies, around 2 GHz, since the dielectric properties in agricultural products are primarily influenced by their ionic conductivity of fluids contained in their cellular structure [2]. The dielectric losses decrease with frequency according to [9] due to ionic conductivity.…”

Microwave-Absorbing Properties of Rice Starch

“…These results suggest that water molecules dominated the electromagnetic properties of the rice starch dispersion, whereas the starch had little effect on the value of the RL peak. Microwave heating is greatly affected by the presence of water in foods [18,19]. The 3-mm thickness of the rice starch dispersion was appropriate to reflect the change in the absorption of the whole system.…”

“…Microwave heating is greatly affected by the presence of water in foods [18,19]. The 3-mm thickness of the rice starch dispersion was appropriate to reflect the change in the absorption of the whole system.…”

Estudio de los espectros dieléctricos para el control de calidad de alimentos

“…Este modelo puede aplicarse en alimentos coloidales para comprender el comportamiento de lípidos, proteínas e hidratos de carbono . Otros constituyentes como pueden ser alcoholes o azúcares, interaccionan con las moléculas de agua provocando un cambio en la frecuencia de relajación debido a la formación de , Kent y Jason, 1975, Mudgett et al, 1977 Swami y Mudgett, 1981; Nelson y Russell, 1986;Ohlsson, 1987). Dichos modelos consideran el alimento constituido por una matriz sólida insoluble y una disolución acuosa dieléctricamente muy activa.…”

“…Por otra parte, la modelización resulta más compleja a medida que aumenta el grado de estructuración ; si además el alimento tiene estructura celular el nivel de complejidad es máximo porque se presentan numerosos mecanismos dieléctricos de manera simultánea (véase la sección 1.2.2) que dificultan la comprensión o predicción del valor de las propiedades dieléctricas o de la forma de los espectros completos. Muchos autores han utilizado ecuaciones para predecir el comportamiento dieléctrico de este tipo de alimentos , Kent y Jason, 1975, Mudgett et al, 1977Swami y Mudgett, 1981;Nelson y Russell, 1986;Ohlsson, 1987). Dichos modelos consideran el alimento constituido por una matriz sólida insoluble y una disolución acuosa dieléctricamente muy activa.…”