# Helium Atmospheric Pressure Plasma Jet Source Treatment of White Grapes Juice for Winemaking
## 3 Results and Discussion
### Plasma Source Electro-Optical Characterization
#### 3.1.2 Plasma Source Optical Diagnosis
For the case when plasma met the must (Figure 3 right side graphs), the dominant peaks were found around 308 nm, corresponding to OH radicals, in the UVB region. Smaller peaks of molecular nitrogen and molecular nitrogen ions were found (at the same peaks wavelengths) in the UVA region. Again, no significant lines/bands were identified in the UVC region (bellow 280 nm). Since atmospheric pressure plasma treatments are usually seen as oxidative methods, and due to the fact that phenols (the main component of white wines) are the primary support for oxidation, it is reasonable to understand the importance of knowing the plasma RONS and the changes in the UV-Vis absorption spectra of wine. Besides plasma reactive species, another important parameter in plasma treatment of matter is the plasma temperature. Since the studied plasma source is at atmospheric pressure, working in gas flow, it is easy to assume that this is a non-thermal plasma, meaning that the temperature of the electrons differs from the temperature of the ions, and that of the neutrals. In this context, of the electric discharges characteristic temperatures, it is interesting to determine these values in order to understand how these plasmas can interact with matter. Moreover, using simulation software like Lifbase [103] and Spectrum Analyzer [104], we determined, from the acquired plasma emission spectra, the characteristic plasma temperatures, such as: the rotational temperature of OH radicals, the rotational temperature of nitrogen molecular ions \(N_{2}^{+}\), the vibrational temperature of nitrogen molecules \(N_{2}\). Then, a spot thermal camera (FLIR TG165, pointed onto the surface of the must during the plasma treatment) and k-type probe thermocouple (placed bellow as well as in the Petri dish, via a PeakTech 3415 USB DMM digital multimeter) were used for monitoring the plasma gas temperature as well as the surface temperature in front of the plasma (Table 3). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \(\lambda\) & **Transition** & \multicolumn{2}{c}{**Normalized Intensity**} & \multicolumn{1}{c}{**E\({}_{k}\)**} \\
**[nm]** & & **in Midair** & **with Must** & **[eV]** \\ \hline
308 OH & \((A^{2}\Sigma^{+})\leftarrow(X^{2}\Pi_{i})\) & 0.333 & 1 & 4 \\
337 N\({}_{2}\) & \((C^{3}\Pi_{u})_{v^{\prime}=0}\leftarrow(B^{3}\Pi_{g})_{v^{\prime\prime}=0}\) & 0.782 & 0.927 & 11.0 \\
391 N\({}_{2}^{+}\) & \((B^{2}\Sigma^{+}_{u})_{v^{\prime}=0}\leftarrow(X^{2}\Sigma^{+}_{g})_{v^{\prime \prime}=0}\) & 1 & 0.299 & 18.7 \\
486 H\({}_{\beta}\) & \(4\gets 2\) & 0.070 & 0.117 & 12.7 \\
587 He & \((3d)\leftarrow(2p)\) & 0.067 & 0.078 & 23.1 \\
667 He & \((3d)\leftarrow(2p)\) & 0.058 & 0.091 & 23.1 \\
706 He & \((3s)\leftarrow(2p)\) & 0.073 & 0.088 & 22.7 \\
728 He & \((3s)\leftarrow(2p)\) & 0.067 & 0.076 & 22.9 \\
777 O & \(3s\ ^{5}S^{0}_{2}\gets 3p\ ^{5}P_{i}\) & 0.097 & 0.111 & 10.7 \\
844 O & \(3s\ ^{3}S^{0}_{1}\gets 3p\ ^{3}P_{i}\) & 0.054 & 0.087 & 11.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Normalized spectral lines and bands intensity observed in the discharge with energies E\({}_{k}\) of the upper states from [105,106]. As can be observed from the temperature values estimated through spectroscopic measurements, the rotational temperature of hydroxyl radicals and nitrogen molecular ions, which is often attributed/equaled to the gas temperature in many plasma sources reported in literature (especially DBD based sources), was determined to be 340-355 K (66 to 80 \({}^{\circ}\)C). These values corresponded to a'spectroscopic temperature' meaning energies that those plasma species (OH and N\({}_{2}^{+}\) ) could achieve and could be used in the plasma environment to initiate various physico-chemical reactions/processes that could take place on the surface or in the plasma volume. The gas temperature of the gas/liquid in interaction with the plasma was measured, the values being around 35-40 \({}^{\circ}\)C (\(\pm\)1.5 to 3 \({}^{\circ}\)C).