Dielectric Properties of Fish Flesh at Microwave Frequency

Abstract

We investigated the dielectric properties of fish flesh samples, which are the most important parameter in microwave heating. Both raw and preheated samples were investigated since the microwave is used not only for heating, but also for reheating. The dielectric properties of three kinds of fish commonly consumed in Japan were measured from 10℃ to 90℃, at 10℃ intervals. The influences of frequency, temperature, moisture content, lipid content, protein denaturation, and heat treatment on dielectric properties were examined. With increasing temperature, the dielectric constant of the raw samples decreased more sharply than that of the preheated samples, which was due to moisture loss during heating caused by protein denaturation. To investigate the influence of protein denaturation, Lichtenecker's formula was applied to estimate the dielectric properties of solid fish flesh. Results showed that the dielectric properties of fish flesh related to temperature were predictable by regression equations. Moisture content was the most important factor influencing the dielectric properties of the fish flesh samples during heating (reheating), while no significant effect was found to be directly caused by changes in the protein structure of fish flesh after denaturation.Keywords: microwave heating, dielectric properties, dielectric constant, dielectric loss factor, protein denaturation, lichtenecker's formula *To whom correspondence should be addressed. E-mail: sakai@kaiyodai.ac.jp IntroductionWith the development of heating technologies for food processing, microwave (MW) heating has increasingly been employed for both cooking and reheating due to its great speed and convenience (Mara et al., 2008). MW heating is described by Maxwell's equations, and the dielectric properties are the most important physical properties associated with MW heating from an engineering viewpoint (Icier and Baysal, 2004;Sosa-Morales et al., 2010). Dielectric properties determine the interaction of electromagnetic energy with the materials (Tanaka et al., 2008), and provide a better understanding on the behavior of MW heating (Mudgett, 1994;Ahmed et al., 2007b) in a selected frequency range. The dielectric constant (εʹ) and dielectric loss factor (εʺ) determine the heat generation and change in response to the ingredients and temperature of the food when heated by MW . εʹ and εʺ represent the real and imaginary units, respectively. Complex relative dielectric properties are de-

Influence of composition, temperature, and frequency on dielectric properties of selected saltwater and freshwater fish

“…Changes in the protein structure during protein denaturation have no direct effect on dielectric properties, indicating that moisture content was the most influential factor on the dielectric properties of fish flesh. [13] Literature shows that the ash content has no significant effect on the dielectric constant of meat, but the dielectric loss factor increases with the increase of ash content. [31] However, the dielectric loss factor of the Hairtail was higher than other fishes, which shows that the effect of moisture content and ionic conductivity on the dielectric loss factor is greater than that of the ash content.…”

“…The dielectric properties increased gradually with increasing moisture content below −5°C, and the difference in the dielectric properties between different moisture content levels continuously increases with the rising temperature, especially in the temperature range from −5°C to 0°C. Liu et al [13] measured the dielectric properties of raw and preheated red Sea Bream (Pagrus major), Yellowtail (Seriola quinqueradiata), and Atlantic Salmon (Salmo salar) over the temperature range of 10-90°C and frequency of 200-3660 MHz. The dielectric properties of the red Sea Bream were slightly higher than the other two species.…”

Electromagnetic properties of crayfish and its responses of temperature and moisture under microwave field

“…Heat transfer: The internal power‐generation term, which represents the “heat source” term, was proposed based on the coupling of the electromagnetic field with the energy balance equation. The Fourier's equation combined with quasi‐static electromagnetic field was used to describe the energy conversion (Liu et al., 2012): where ρ is the density (kg/m 3 ), C p is the specific heat (kJ/[kg∙°C]), t is the axial coordinate, k is the thermal conductivity (W/[m∙°C]), T is the temperature of crayfish (°C).…”

“…where m i and m j are the weight of the homogenate before and after being dehydrated, respectively. The E5071C vector network analyzer (Agilent, Santa Clara, CA, USA) with an open-ended coaxial probe (85070E, Agilent) was used to determine the dielectric properties of homogenates from crayfish different parts in a constant humidity and temperature chamber (Cao et al, 2018;Liu et al, 2012;Tanaka et al, 1999). The analyzer has been pre run for at least 30 min before the test, and the probe was calibrated successively by the air, metal shortcircuit element, and deionized water (Cao et al, 2018).…”

“…Heat transfer: The internal power-generation term, which represents the "heat source" term, was proposed based on the coupling of the electromagnetic field with the energy balance equation. The Fourier's equation combined with quasi-static electromagnetic field was used to describe the energy conversion (Liu et al, 2012):…”