## 3 Results
### Changes in the Aroma Profile Induced by DBD Plasma  
The changes in the volatile compounds profile induced by plasma treatment directly impact the pineapple juice aroma. Thus, it is essential to understand how the changes in volatile composition affect the sensory quality of the juice. Current knowledge of odor thresholds and descriptors of individual compounds can produce a satisfactory aroma profile of the juice without requiring trained sensory panelists, as has been done for many years in the perfume industry [36]. Table 3 presents the odor description notes and the odor threshold value of the main volatile compounds in the pineapple juices. The most relevant descriptive notes for the aroma composition of the pineapple juices were fruity, sulfurous, fatty, and waxy. To discuss the main changes in the aroma of the treated juices, each processing condition was compared with the descriptive notes profile of the natural juice (untreated). Significant changes in the aroma profile could be noted in the conditions studied. Plasma processing at a low frequency (50 Hz) promoted changes mainly in the fruity descriptor of the pineapple juice aroma. Although the characteristic esters from pineapple juice changed after processing, the total contribution of the fruity descriptor remained similar after a short processing time (10 min). However, at longer processing times (20 min), the significance of the fruity descriptor decreased but remained as the primary descriptor (Figure 2). The reduction in the significance of the fruity descriptor was caused by the decrease in the concentration of methyl 2-methyl butanoate (\(-52\%\)), ethyl 2-methyl butanoate (\(-24\%\)), methyl hexanoate (\(-78\%\)), and ethyl hexanoate (\(-80\%\)). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Frequency** & **Hydroxyl Radical** & **Hydrogen Peroxide** & **Superoxide Anion** \\
**(Hz)** & **Hydroxyl Radical** & **Hydrogen Peroxide** & **Superoxide Anion** \\ \hline
50 & 1.0 \(\pm\) 0.0 & 0.9 \(\pm\) 0.1 & 0.3 \(\pm\) 0.1 \\
500 & 0.9 \(\pm\) 0.1 & 1.0 \(\pm\) 0.0 & 1.0 \(\pm\) 0.0 \\
1000 & 0.4 \(\pm\) 0.1 & 1.0 \(\pm\) 0.0 & 0.2 \(\pm\) 0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Reactive oxygen species formed in pineapple juice subjected to dielectric barrier discharge plasma under different operating conditions. Results are presented in normalized values. Number of replicates = 3. \begin{table}
\begin{tabular}{l c c} \hline \hline  & **Primary Odor Description** & **Secundary Odor Description** & **Odor Threshold (mg/L Water)** \\ \hline Ethyl acetate & ethereo & - & 25 \\ Methyl butanoate & fruity & apple/ sweet & 0.076 \\ Methyl 2-methyl butanoate & fruity & ethereal & 0.00025 \\ Ethyl 2-methyl butanoate & fruity & sharp/sweet & 0.0003 \\ Methyl hexanoate & fruity & ethereal & 0.084 \\ Ethyl hexanoate & fruity & sweet & 0.001 \\ Methyl 3-(methylthio)propionate & sulfurous & - & 0.180 \\ Ethyl 3-(methylthio)propanoate & sulfurous & - & 0.007 \\ Methyl octanoate & waxy & - & 0.200 \\
1.3.5-undecatriene & fruity & fresh/green & 0.00002 \\ Octanoic acid & fatty & - & 0.910 \\ Ethyl octanoate & waxy & - & 0.005 \\ Decanal & aldehyde & - & 0.030 \\
5-Hydroxymethyl-2-furaldehyde & fatty & - & 100 \\ Phenethyl acetate & floral & - & 0.650 \\
5-Butyldihydro-2(3H)-furanone & fatty & - & 0.007 \\ Methyl linoleate & ethereo & - & 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Primary and secondary odor descriptors of the main volatile compounds found in pineapple juice and their odor thresholds in water. The secondary descriptive notes of the fruity aroma were also evaluated since the fruity aroma is highly dominant in pineapple juice. The natural pineapple juice presented a balanced profile on the fruity secondary descriptors, among sweet, ethereal, and fresh notes. At low frequencies and long exposure time (50 Hz/20 min), the samples lost the fresh note, and the ethereal note dominated the fruity aroma. This impact was due to the absence of the 1,3,5-undecatriene after plasma treatment.