## 3 Results and Discussion
Since the mechanism of this type of aggregation is different on a molecular level compared to the enzyme-induced process, the values and the variation of viscosity over time show observable differences, as can be seen in Figure 4. One of the most prominent differences can be found in the order of magnitude of values: compared to the enzyme-induced  
Figure 3: Correlation between the apparent viscosity (\(\eta\)) and the dielectric constant (\(\epsilon^{\prime}\)) during 10–25 min (**a**) and 30–60 min (**b**) of the enzyme-induced coagulation process. samples, the highest level of viscosity exceeds 48 mPa-s, whereas, in the case of the former process, the maximum value resides around 460 mPa-s. From a technological point of view, this is perfectly reasonable, of course; enzyme-induced coagulation is applied during cheese production, while acid coagulation is used in yogurt manufacturing. Differences, however, can be found in trends of change as well. In the first phase (0-55 min), a slight increase can be detected, which is followed by a steep rise up to the maximum value of viscosity (55-95 min). This indicates that during acid coagulation, to reaching the point of clot solidification takes considerably more time than enzyme-induced coagulation. The dielectric constant also acts differently compared to the former process. In the first phase, a slight decrease can be observed, which is then followed by a steeper, characteristic drop in values. These reflections can be explained by the molecular mechanism that happens during acid coagulation. In the first 55-60 min, bacteria continuously convert lactose into lactic acid, which reduces the electrical susceptibility of the medium since lactose molecules are easier to polarize than lactic acid. [PERSON] et al. also verified that the presence and concentration of lactose have no effect on the change trends in the dielectric constant but affect its value at a given frequency in milk [31]. Higher lactic acid concentrations manifest in a higher dielectric constant in an aqueous system [32], but in multicomponent systems, such as milk, the fat, content, and the structural changes in protein molecules also determine the dielectric behavior. The increasing presence of lactic acid progressively decreases the pH, and when it falls below pH = 5, the destabilization of casein micelles takes place. When the pH ultimately reaches the isoelectric point of casein micelles, the aggregation (i.e., the formation of a protein network) begins. In our case, the pH of the sample decreased from its initial 6.5 \(\pm\) 0.05 value down to 4.5 \(\pm\) 0.03. This type of sol-gel transformation in terms of dielectric behavior is manifested in the fact that, on the one hand, the casein aggregates (and then chains) increasing in size reduce the electrical susceptibility of the basic material matrix due to their molecular structure and stability [33], i.e., they \"respond\" to the electromagnetic field strength to a lesser and lesser extent. This leads to a decrease in the rate of energy absorption and energy storage capacity [34] (characterized by a decrease in the dielectric constant). On the other hand, as the casein micelles destabilize, the average micelle concentration of the medium decreases,  
Figure 4: Change in apparent viscosity (\(\eta\)) and dielectric constant (\(\epsilon^{\prime}\), f = 400 MHz) versus time during the acid coagulation of raw milk. which in turn reduces the conductivity of the material--the specific conduction loss thus becomes smaller as the process progresses. The charge of the protein's surface also affects the extent of the dielectric constant, as the casein micelles have lost their net surface charge prior to the destabilization phase, which can also contribute to the decrease in the dielectric constant [35]. To determine the connection and correlation between the rheological and dielectric characteristics, we used the same method discussed earlier during the enzyme-induced coagulation, i.e., establishing a logarithmic-transformed linearized function of the values.