## 3 Results
### Changes in the Aroma Profile Induced by DBD Plasma
This compound was reported in some studies as an important aroma contributor to the pineapple odor in many cultivars [37; 38]. The sulfur descriptor increased at low frequency and long processing time (50 Hz/20 min) because of the increase in the mass fraction of methyl 3-methyl(thio)propanoate and ethyl 3-methyl(thio)propanoate. The fatty descriptor became more intense after low-frequency cold plasma application in all processing times, which was caused by a significant increase in the mass fraction of 5-butyldihydro-2(3H)-furanone and octanoic acid. The increase was more significant at longer processing times. The waxy aroma increased after 10 min of exposure at low frequency due to the increase in ethyl octanoate content (>100%). Further processing of the juice (50 Hz/20 min) reduced the intensity of the waxy aroma due to the significant reduction in methyl and ethyl octanoate concentrations, the two compounds that give the waxy aroma to pineapple juice. According to the reaction pathway observed for esters (Figure 1), methyl and ethyl octanoates decayed into esters with shorter chain lengths, which present fruity notes. Extended processing of pineapple juice (20 min) resulted in the appearance of an aldehyde aroma note, which emerged from the formation of decanal, which was formed from the scission of the small amounts of fatty methyl esters in the juice [18]. The OAV of the aldehyde aroma was insignificant compared to the other OAVs of the five main aroma descriptors, and the presence of this note did not compromise the sensory quality of the juice. Under a mid-range frequency (500 Hz), the impact of the fruity descriptor in the aroma increased. The secondary descriptive notes of the fruity aroma showed a high increase  
Figure 2: Aroma descriptors radar for pineapple juice subjected to dielectric barrier discharge plasma application: (**a,b**) OAV of the untreated, 50 Hz/10 min, and 50 Hz/20 min samples; (**c,d**) OAV of the secondary notes of the fruity descriptor for the untreated, 50 Hz/10 min, and 50 Hz/20 min samples. of the fresh note at an extended processing time (20 min). The sweet and ethereal notes remained at the same levels as the natural juice. The increase in the fresh note was related to the rise in the concentration of the 1,3,5-undecatriene (Figure 3). The results obtained from low frequency (50 Hz) and mid-range frequency (500 Hz) shows the importance of the excitation frequency in cold plasma applications, since the changes induced on the aroma profile were significantly different between these two frequencies. Such differences have also been perceived for other fruit juices, such as camu-camu [18], orange [17], and coffee [20] subjected to plasma treatment. The changes in volatile compounds after plasma treatment at 500 Hz were more intense than in the other frequencies, probably due to the higher content of reactive oxygen radicals formed during processing. The changes were marked by the increase in the mass fraction of thio compounds and the decrease in the mass fraction of short-chain esters. The increased mass fraction of thio compounds, mainly methyl 3-methyl(thio)propanoate and ethyl 3-methyl(thio)propanoate, had a direct effect on pineapple juice aroma with an increase of 113% in the sulfuron's notes after 20 min of treatment. The fatty and waxy aromas also increased in the 500 Hz plasma treatment. The fatty aroma became 258% more intense due to the significant increase in the concentration of 5-butyldihydro-2(3H)-furanone and octanoic acid in the first 10 min of treatment. Further increase in the fatty aroma was observed after 20 min of treatment due to the formation of 2-furaldehyde-5-hydroxymethyl. The increase in ethyl octanoate intensified the waxy aroma. In fresh pineapple juice, the strength of the waxy aroma is given by equal contributions of ethyl- and methyl-octanoate. In the plasma-treated juice, methyl octanoate was converted into ethyl octanoate (Figure 1), and the strength of the waxy aroma was caused mostly by the contents of ethyl octanoate.