## 3 Results and Discussion
### Modifications in the Aroma Profile  
Table 1 presents the odor descriptions and thresholds of the volatile compounds of pasteurized orange juice. Figure 4 shows the changes in the orange juice's five primary odor descriptors. The chemical reactions induced by the plasma treatment on the orange juice volatiles directly affected the aroma profile of the juice, as well as some significant changes in the strength of the citrus, aldehyde, and floral descriptors.  
Considering the pasteurized orange juice's odor activity value (OAV), its aroma is characterized by 44.3% citrus, 23.3% aldehyde, 15.2% floral, 9.7% terpenic, and 7.5% herbal descriptors. The changes induced by the plasma treatment tended to considerably reduce the OAV of the citrus descriptors and increased the aldehyde and floral descriptors' OAV.  
The lower contribution of the citrus aroma in the plasma-treated orange juice reflected the reduction in limonene and 3-carene concentrations. Even when treated at low fluences (100 to 200), conditions in which an increase in limonene content was observed, the OAV of the citrus descriptors decreased due to the significant reduction in 3-carene content (>31%), which has a much lower odor threshold (0.044 mg/L) than limonene (1.04 mg/L).  
The increase in aldehyde aromas was due to the significant increase in octanal, nonanal, decanal, and dodecanal concentrations. Plasma-treated orange juice presented an aldehyde contribution toward its aroma, ranging between 19.5 to 33.9% of the juice OAV. The aldehyde aroma decreased at low fluences (100 to 200) or short treatment times (10 min) due to the formation of a-linaloid that pushed the aroma toward a more floral ascent. At higher fluences or longer treatment times, the aldehyde aroma considerably increased due to the formation of aldehydes and the isomerization of \(\alpha\)-linaloid into oxygenated terpen with higher odor thresholds. Even with the increase in aldehyde and floral descriptors, the glow plasma treatment maintained the citrus descriptors as primary odors in the pasteurized orange juice.  
Although there was a partial shift from the citrus descriptors toward the aldehyde descriptors, both octanal and nonanal are considered two important contributors to orange juice flavor because they have an orange-like aroma. Thus, in practice, this aroma descriptor shift does not contribute negatively to the aroma of orange juice.  
Significant changes were observed regarding the contribution of the floral descriptor, caused by the changes in the concentration of linalool. This descriptor contributed to 15.2% of the pasteurized orange juice OAV, whereas its contribution in the plasma-treated juice ranged from 10.8 to 21.8%, depending on the operational condition applied. Linalool has a lavelander-like smell, which is considered calming and soothing. This fragrance agent is used in most hygiene items, including shampoos, soaps, lotions, and detergents; thus, its smell is well-linked with cleaning products. Its expression in foods may cause a strange perception. In orange juice, linalool is a desirable compound and positively contributes to the orange juice aroma. However, linalool is the precursor of a-terpineol, which is one of the three most detrimental compounds in orange juice quality, along with 4-vinyl guaiacol and 2,5-dimethyl-4-hydroxy-3-(2H)furanone (DMHF). The formation of high concentrations of linalool should be avoided to ensure a low concentration of a-terpineol during storage.  
The glow discharge plasma treatment increased the contents of aldehydes in the pasteurized orange juice, increasing significantly the aldehyde notes of the juice and contributing to the production of a pasteurized orange juice with a better aroma quality. Thus, glow discharge plasma processing could be employed to improve the aroma of pasteurized orange juice.  
Figure 4: Aroma profile radar for the pasteurized orange juice and plasma-treated orange juice: (a) treated at 10 mL/min; (b) treated for 30 min.