## 1 Introduction
A similar theory of rupture of the cell membrane assumes that the destruction of the cell membrane through ruptures occurs as a result of the generated electrical voltage. A slightly different cause of microbial inactivation is indicated by the coupled magnetic field theory, according to which it is electromagnetic energy, through a coupled influence on important elements for bacteria, i.e., on protein or DNA molecules, that causes its death [3]. In the microwave treatment used in our experiment, the microwave field was densified by means of a specially constructed waveguide, which is why device manufacturer Plazmatronika called this method a \"concentrated microwave field\" (CMF). The term \"concentrated microwave field\" may be ambiguous, but it has been traditionally used in Poland among researchers and food technologists for about 20 years. In world literature, other terms related to this technology are popular, such as: \"single-mode-type microwave heating\" [17], which results from the use of a standardized waveguide, alternatively referred to as \"single-mode microwave cavity\" [18; 19; 20]. The authors decided to keep the traditionally used name of this technology as CMF. The dielectric properties of the microwave treated food products are the main parameters taken into account in the calculations related to the conversion of microwave energy into heat. The most frequently used concept is the relative complex permittivity \(\varepsilon^{*}\), referring to the treated raw material, which has the form of a complex number consisting of the real part \(\varepsilon^{\prime}\) and the imaginary part \(\varepsilon^{\prime\prime}\) according to the following formula [3; 21]:  
\[\varepsilon^{*}=\varepsilon^{\prime}-\mathrm{j}\varepsilon^{\prime\prime}\]  
where: \(\varepsilon^{*}\)--relative complex permittivity,  
\(\varepsilon^{\prime}\)--electric permeability,\(\epsilon^{\prime\prime}\)**--dielectric loss factor,**  
**j**--imaginary unit of a complex number  
**The real part** \(\epsilon^{\prime}\) **describes the ability of a material to store electrical energy whereas the imaginary part** \(\epsilon^{\prime\prime}\) **is related to the loss of electrical energy in terms of heat dissipation** **[**22**]****. The ratio of the dielectric loss factor** \(\epsilon^{\prime\prime}\) **and the dielectric permittivity** \(\epsilon^{\prime}\) **is expressed as a tangent delta and is the same as the ratio of the relative dielectric loss coefficient and the relative dielectric permittivity according to the formula** **[**3**]****:**  
\[\text{tg}\ \delta=\epsilon^{\prime\prime}/\epsilon^{\prime}=\kappa^{\prime \prime}/\kappa^{\prime}\]  
**where:** \(\text{tg}\ \delta\)**--tan delta**  
\(\epsilon^{\prime}\)**--electric permittivity,**  
\(\epsilon^{\prime\prime}\)**--dielectric loss factor,**  
\(\kappa^{\prime}\)**--relative electric permittivity, also called the dielectric constant,**  
\(\kappa^{\prime\prime}\)**--relative dielectric loss factor. **  
**The relationships between the values of** \(\epsilon\) **and** \(\kappa\) **can be described as** \(\kappa^{\prime}\)**=** \(\epsilon^{\prime}/\epsilon_{\text{o}}\) **and** \(\kappa^{\prime\prime}\) **=** \(\epsilon^{\prime\prime}/\epsilon_{\text{o}}\) **where** \(\epsilon_{\text{o}}\) **is the permittivity of the vacuum (**\(\epsilon_{\text{o}}\) **= 8.854** \(\times\) **10**\({}^{-12}\) **F m**\({}^{-1}\)**). The dielectric properties of raw materials subjected to the influence of the microwave field also depend on the temperature of the process and the frequency of the microwave waves used** **[**3**]****.