## 2 Results and Discussion
### Volatile Characterization
#### 2.1.1 HS-SPME-GC-MS Analysis
The detection of certain amounts of allyl derivatives in onion processed product is in agreement with previous literature [20]  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Compound**} & \multirow{2}{*}{**RI\({}_{\text{ref}}\)**} & \multirow{2}{*}{**RI\({}_{\text{cal}}\)**} & \multirow{2}{*}{**Identification**} & \multicolumn{3}{c}{**Dry Onion (ug g\({}^{-1}\))**} & \multicolumn{3}{c}{**Dry Onion with**} \\  & & & & & **Ekles** & **Rings** & **Fakes** & **Rings** \\ \hline \hline \multirow{2}{*}{**ketones** 6-methyl-5-hepten-2-one} & \multirow{2}{*}{1338} & \multirow{2}{*}{1340} & \multirow{2}{*}{126, 69, 108} & \multirow{2}{*}{0.04 a} & \multirow{2}{*}{0.03 a} & \multirow{2}{*}{0.03 a} & \multirow{2}{*}{0.03 a} \\  & & & & & & & \\ \hline \hline \multirow{2}{*}{**carboxylic acids** 1883 25  
Aldehydes--a total of 16 aldehydes were identified in the volatile profile of the dried onion samples, 4 of which never reported in this type of samples so far (2-methyl propanal, pentanal, octanal and furfural). The total content of aldehydes was slightly higher in dried onion flakes (1.80 \(\mu\)g g\({}^{-1}\)) than in dried onion rings (1.31 \(\mu\)g g\({}^{-1}\)) and the content was higher in both the samples when they were analyzed in the presence of ascorbic acid. This higher content in the presence of ascorbic acid was almost completely due to octanal, furfural and decanal, absent or present in negligible amounts when the samples were analyzed in the absence of ascorbic acid and present in significant amount when the samples were analyzed in the presence of ascorbic acid--these three aldehydes were not found in a previous study analyzing dried onion samples [12]. If furfural is a well-known degradation products of ascorbic acid [21], our data pointed out that the presence of ascorbic acid affects the content of octanal and decanal in the volatile profile of dried onion samples. We can hypothesize that the antioxidant activity of ascorbic acid prevents further oxidation of these molecules in the analytical conditions but further investigation should also be performed in future studies to exclude that also these 2 aldehydes are degradation products of ascorbic acid. Regarding the content of the different aldehydes in the samples analyzed in the absence of ascorbic acid, nonanal was only present in trace, while the greatest content was for 3-methyl butanal in dried onion flakes (0.36 \(\mu\)g g\({}^{-1}\)). The content of the most of the identified aldehydes did not significantly differ between dried onion flakes and dried onion rings. The content of the following 5 aldehydes was significantly different and higher in onion flakes--propanal, hexanal, benzaldehyde, Z-2-heptenal and 2-methyl-2-pentenal, with this latter molecule that was reported to be the main degradation product of the lachryatory factor [14]. The presence of high amounts of hexanal and 2-methyl-2-pentenal was recently associated to some off-flavor attributes of onion powder, as humidity [12]; our results show low amount of these two aldehydes (approx. 0.2% of the total VOCs content), this result pointing out that in the analyzed sample this off-flavor can be considered absent. Other VOCs--6 volatile compounds other than aldehydes or S-containing compounds were detected in our samples in low amounts--6-methyl-5-hepten-2-one, nonanoic acid, 2-pentylfuran, 1-octen-3-ol, isopropyl dodecanoate and 2,2,4-trimethyl-1,3-pentenedi diisobutyrate. These VOCs showed slight differences between onion flakes and onion rings and their amount did not change when the samples were analyzed in the presence of ascorbic acid. The only exception was the nonanoic acid, which content strongly increased in the presence of ascorbic acid, which also led to the detection of hexanoic and 2-ethyl hexanoic acids.