# Inactivation of Contaminated Fungi in Rice Grains by Dielectric Heating
## 3 Results and Discussion
### Effect of Dielectric Heating Condition on Fungal Growth  
The rice samples were treated by the heating system at a selected frequency and electric field intensity of 40.68 MHz with 150, 190, 225, 300, and 450 kV/m, respectively. The fungal inactivation on the rice sample was obtained by using temperature with electric field intensity (Figure 7). As seen in Figure 7, the synergies of temperatures and electric field intensities can be divided into nine groups (a-i, which are from the highest to lowest group of the fungal inactivation). The result showed that the fungal inactivation of 100% was obtained at the electric field intensity value \(\geq\) 225 kV/m at the lowest temperature of 90 \({}^{\circ}\)C. Based on statistical analysis, the fungal inactivation in rice grains was significant (\(p\)\(\leq\) 0.05) by the effects of the combination of temperature and electric field intensity. A previous study reported that the effect of both the thermal and non-thermal was caused by the \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Dielectric Constant**} & \multicolumn{3}{c}{**Dielectric Loss**} \\ \cline{2-7}
**Mean \(\pm\) SD** & \multicolumn{6}{c}{**Frequency (MHz)**} \\ \cline{2-7}  & **40.68** & **915** & **2450** & **40.68** & **915** & **2450** \\ \hline _Aspergillus_ sp. BP17 (A) & 31.574 \(\pm\) 0.333 & 18.356 \(\pm\) 0.449 & 16.794 \(\pm\) 0.166 & 48.92 \(\pm\) 0.466 & 5.042 \(\pm\) 0.117 & 4.412 \(\pm\) 0.106 \\ \hline Rice powder (B) & 4.754 \(\pm\) 0.123 & 3.774 \(\pm\) 0.044 & 3.343 \(\pm\) 0.064 & 0.251 \(\pm\) 0.036 & 0.551 \(\pm\) 0.022 & 0.582 \(\pm\) 0.019 \\ \hline Ratio A:B & 6.641 & 4.863 & 5.024 & 194.900 & 9.151 & 7.580 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Dielectric properties of _Aspergillus_ sp. BP17 and rice powder. pasteurization mechanism on micro-organisms at the cellular level [54]. Here, the fungal inactivation of 100% was obtained using 190 kV/m at 100 and 110 \({}^{\circ}\)C, 225 kV/m at 90, 100 and 110 \({}^{\circ}\)C, 300 kV/m at 90, 100 and 110 \({}^{\circ}\)C, 450 kV/m at 90, 100 and 110 \({}^{\circ}\)C (Figure 7). The effect of different temperatures on fungal inhibition has been reported including _Aspergillus_ sp. in canned strawberries (94 \({}^{\circ}\)C) [55] and grape juice (85 \({}^{\circ}\)C) [56], _Aspergillus niger_ (90 \({}^{\circ}\)C) and _Aspergillus flavus_ in oil seed (90 \({}^{\circ}\)C) [19], _Aspergillus flavus_ in Khao Dawk Mali 105 (90 \({}^{\circ}\)C) [57], and the other _Aspergillus_ species with a neosortorya-morph (80-90 \({}^{\circ}\)C) [58]. Figure 6: The relative electric field intensity and temperature in the heating system. Figure 7: The relative electric field intensity and temperature on fungal growth. Average \(\pm\) standard deviation from three replicate experiments. Different letters in the same column are considered significantly different according to [PERSON]’s multiple comparison test (\(p\leq 0.05\)). To visualize the effect of dielectric heating on fungal growth based on different electric intensities, six samples including one non-treated sample (control) and five treated samples (150, 190, 225, 300, and 450 kV/m ) were selected to show fungal inactivation. Figure 8 shows the fungal growth on PDA after rice samples were treated with different electric intensities at 90 \({}^{\circ}\)C. Fungal mycelium was grown from rice grains in the control agar plate. On the contrary, fungal growth from rice grains was deceased based on 150 kV/m and 190 kV/m, and the hyphae were not germinated from rice grains that were treated with electric field intensity value \(\geq\) 225 kV/m at 90 \({}^{\circ}\)C. This indicates that the optimal conditions of dielectric heating (combination of 225 kV/m and 90 \({}^{\circ}\)C) are powerful for fungal inactivation in rice grains by dielectric heating. [PERSON] reported that the electric field (194 kV/m) has a non-thermal effect on the cellular membrane (in the air of electrode gaps) [59].