## 3 Results and Discussion
### Modifications in the Volatile Profile
Furthermore, higher flow rates mean a lower plasma residence time inside the treatment chamber since a vacuum pump controls the pressure and plasma content in the system. Herein, the discussion is based on the fluence and residence time because they showed a higher correlation with the data. The main class of compounds in orange juice are terpenoids. Figure 3 shows the chemical reaction pathways observed in terpenoid compounds during glow discharge plasma processing. Figure 2: Heat map showing the changes in the mass fraction of volatile components with the untreated juice as a basis for comparison. Blue and red colors indicate an increase and decrease in concentration, respectively. Light colors indicate changes between 0 and 50% in the component’s mass fraction. Darker colors indicate changes above 50% in the component’s mass fraction. Reactive oxygen species, such as oxygen singlet, superoxide radical, hydroxyl radical, ozone, and hydrogen peroxide, are formed during plasma application and contribute to the production of peroxides and alcohols [26; 27]. Direct oxidation of limonene and the terpenyl radical was observed due to the formation of p-mentha-6,8-diene-2-hydroperoxide, perillaldehyde, and p-mentha-2,8-dienol, which increased significantly after plasma treatment. The selectivity of these reactions followed the order: perillaldehyde > p-mentha-2,8-dienol > p-mentha-6,8-diene-2-hydroperoxide. The highest yield of these three oxygenated products occurred at a flow rate of 20 mL/min, which was already shown to be the flow rate that leads to high aroma modification [6]. The highest yield of these oxygenated products occurred at a fluence of 600 for 20 and 30 mL/min flow rates. The increase in oxygenated products was also marked by the decrease in \(\gamma\)-terpinene, p-cymene, and terpinolene, which are in equilibrium with limonene (Figure 3). The mass balance of components indicates that this equilibrium shifts from the limonene isomers toward oxygenated products. The content of compounds derived from the pinenyl radical (\(\alpha\)-pinene, \(\beta\)-pinene, camphene, sabinene, and 3-carene) did not present a clear trend. Camphene, \(\alpha\)-pinene, and sabinene were the compounds most affected by the plasma treatment, exhibiting the greatest percentual changes. Overall, the increase in pinenyl-derived compounds occurred at fluences which produced less oxygenated products. Thus, the pinenyl-derived compounds are favored under operating conditions that do not induce extended oxidation and hydrolysis of limonene and the terpenyl radical. In a previous work of our group on plasma processing of camu-camu juice [6], the selectivity followed the order: \(\beta\)-pinene > \(\alpha\)-pinene > camphene. There was a slightly  
Figure 3: Putative chemical pathways observed in pasteurized orange juice during glow discharge plasma treatment. higher formation of \(\beta\)-pinene instead of \(\alpha\)-pinene, but with camphene still showing the lowest selectivity among these pinenyl radical-based compounds. This selectivity was the same with orange juice when considering the mass balance of components (not the percentual change). The contents of sesquiterpenoids in orange juice were low, accounting for only 2.5% of the mass of volatiles. Germacrene D and eremophila-1(10),11-diene were the only sesquiterpenoids found in the volatiles of pasteurized orange juice. There was a slight increase in the concentration of these two compounds when processing at 10 mL/min, whereas a higher increase was observed at higher plasma flow rates (20 and 30 mL/min). A significant increase in eremophila-1(10),11-diene (220%), and germacrene D (234%) concentrations were observed at 20 mL/min after 30 min of treatment. The formation of these compounds comes from the farnesyl cation, which can be formed from non-volatile compounds, and thus, is not detected by gas chromatography [28; 29; 30; 31; 32].