# 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  
The Optical Emission Spectroscopy (OES) characterization of the plasma source in mid-air, as well as the OES spectra at the interface plasma-must are presented in in Figure 3.  
Figure 2: Typical voltage–current waveforms of the He–appj in mid air (dash line) and interacting with the white must (short dot line). Emission spectra shown in the plasma emitted light graphs, in the UV-Vis-NIR range (200-1100 nm) of the plasma jet (at 5 mm from the discharge tube nozzle) contained signatures of atomic and molecular excited species. The molecular bands, present in the low wavelength region, were assigned to hydroxyl radicals, neutral nitrogen molecules and nitrogen molecular ion. The OH radical presented signatures between 306-310 nm. Bands of the molecular nitrogen (\(N_{2}\)) were seen between 315-380 nm and 399-405.9 nm. The nitrogen molecular ions (\(N_{2}^{+}\)) had bands at 391.4 nm, 427.8 nm and 470.0 nm. The generation and excitation of \(N_{2}\) (the second positive nitrogen system) and \(N_{2}^{+}\) (first negative nitrogen system) were based on the Penning effect of He metastability. Around 486 nm the atomic line corresponding to the emission of H\({}_{\beta}\) was observed. Atomic lines were assigned to helium atoms (lines at 588.8 nm, 668.5 nm, 706.6 nm and 727.5 nm), as working gas, and to oxygen atoms (lines at 777.8 nm and 845.5 nm) as products of ambient O\({}_{2}\) and H\({}_{2}\)O dissociation [8,11,16,21,101,102]. The presence of other excited species beside the working gas-He, suggests that these reactive oxygen and nitrogen species (RONS) can and will participate in the white grape must sample treatment. Moreover, the importance of some plasma active species changed in the case of interaction with must, as seen in the third line (300-750 nm range). More precisely, it was about the changes regarding the intensity of the hydroxyl radical bands, of the bands of nitrogen molecules as well as of the bands of molecular nitrogen ions. In the case of He-appj running in mid air, as also reported in the literature for such discharges, the bands of molecular nitrogen ions were important in intensity in the emission spectrum, often being used to normalize the entire spectrum for further spectroscopic analyses [8,11,16,21,91]. Thus, as seen in Figure 3, for appj in air, the highest intensity was attributed to the molecular nitrogen ion band, centered at 391 nm. It was followed by the intensities of the molecular bands of nitrogen (337 nm, 357 nm, 315 nm), respectively of the band  
Figure 3: The emission spectra of the He-appj in mid air (**left side**) and interacting with the white must (**right side**). corresponding to the OH radicals (308 nm). The normalized intensities can be quickly followed in Table 2. In the case of He-appj in interaction with the must, the OES spectra revealed different distribution of intensities of lines and bands. More precisely, the most intense band was now attributed to OH radicals (at 308 nm), followed by the bands of molecular nitrogen (337 and 357 nm). These intensity changes of plasma excited species can be seen and followed both in Figure 3 and Table 2.  
We further used the optical emission spectroscopy, which allowed the estimation of rota-vibrational temperatures, as well as the identification of radiating species in the discharge volume. In Figure 3, an overview of the emission spectrum in the range between 200 and 1100 nm is shown. It can be seen that for the appj in mid air (Figure 3 left side graphs), nitrogen dominated the emission spectrum of the plasma as an essential element in ambient air resulting in peaks at 315, 337, and 357 nm, which were in the so called UVA region (315-400 nm). In addition, smaller peaks were found in the UVB region (280-315 nm), attributed to OH radicals bands. Below 280 nm, no radiation was observed and, thus, we can say that no UVC radiation was emitted by the studied plasma source.