## 2 Results and Discussion
### Volatile Characterization
#### 2.1.1 HS-SPME-GC-MS Analysis
\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\({}_{\text{sat}}\)**} & \multirow{2}{*}{**Identification**} & \multirow{2}{*}{**Dry Onion** (**ug g\({}^{-1}\)**)**} & \multicolumn{2}{c}{**Dry Onion with**} \\  & & & & **Ions** & & **Fakes** & **Rings** & **Fakes** & **Rings** \\ \hline \multicolumn{1}{c}{**monosulfides**} & & & \(\Sigma\) & **0.32** & **0.09** & **0.25** & **0.09** \\ dimethyl sulfide & 729 & 729 & 62, 47, 35 & 0.07 b & 0.03 a & 0.06 b & 0.03 a \\ allylpropyl sulfide & 1137 & 1113 & 116, 87, 73 & 0.20 b & 0.04 a & 0.16 b & 0.04 a \\
1-propenylpropyl sulfide & - & 1138 & 41, 116, 74 & 0.05 b & 0.02 a & 0.03 a & 0.02 a \\ \hline \multicolumn{1}{c}{**disulfides**} & & & \(\Sigma\) & **76.76** & **32.89** & **75.04** & **41.74** \\ dimethyl disulfide & 1105 & 1081 & 94, 79, 45 & 0.14 b & 0.03 a & 0.11 b & 0.02 a \\ methylpropyl disulfide & 1263 & 1244 & 80, 122, 43 & 2.56 b & 0.51 a & 2.34 b & 0.73 a \\ methyl\(cis\)-1-propenyl disulfide & 1298 & 1278 & 73, 120, 45 & 2.09 b & 0.20 a & 1.60 b & 0.42 a \\ methyl ally disulfide & 1322 & 1293 & 41, 120, 45 & 0.05 b & 0.02 a & 0.05 b & 0.04 a \\ methyl methyl \(trans\)-1-propenyl disulfide & 1322 & 1302 & 73, 120, 45 & 2.81 c & 0.29 a & 2.47 c & 0.80 b \\ isopropylpropyl disulfide & - & 1331 & 150, 43, 108 & 0.04 b & 0.01 a & 0.03 b & 0.01 a \\ dippropyl disulfide & 1413 & 1391 & 150, 43, 108 & 49.34 b & 2.53 a & 49.77 b & 33.53 a \\ propyl \(cis\)-1-propenyl disulfide & 1450 & 1427 & 148, 106, 41 & 6.69 b & 0.61 a & 6.05 b & 1.38 a \\ allyl isopropyl disulfide & - & 1443 & 57, 148, 106, 41 & 0.46 c & 0.14 a & 0.47 c & 0.25 b \\ propyl \(trans\)-1-propenyl disulfide & 1473 & 1452 & 148, 106, 41 & 11.30 b & 1.53 a & 10.87 b & 3.34 a \\ allyl \(cis\)-1-propenyl disulfide & 1464 & 1480 & 146, 41, 105 & 0.05 b & 0.01 a & 0.04 b & 0.02 a \\ ally \(trans\)-1-propenyl disulfide & 1533 & 1500 & 146, 41, 105 & 0.08 b & 0.03 a & 0.08 b & 0.04 a \\
1-(methylthiopropyl)-2-propenyl disulfide & - & 1876 & 89, 61, 73 & 0.15 ab & 0.07 a & 0.19 b & 0.18 b \\ methyl 1-(proylthio)propyl disulfide & - & 1985 & 117, 75, 41 & 0.44 a & 0.65 b & 0.48 a & 0.82 c \\
1-(_cis_-1-propenylthio)propyl propyl disulfide & - & 2075 & 115, 81, 73 & 0.19 b & 0.09 a & 0.20 b & 0.14 a \\
1-(_trans_-1-propenylthio)propyl proyl disulfide & - & 2080 & 115, 81, 73 & 0.37 b & 0.17 a & 0.29 a & 0.20 a \\ \hline \multicolumn{1}{c}{**trisulfides**} & & & \(\Sigma\) & **41.08** & **5.30** & **41.69** & **11.21** \\ dimethyl trisulfide & 1403 & 1399 & 126, 111, 79 & 6.01 c & 0.49 a & 7.16 c & 1.97 b \\ methyl propyl trisulfide & 1576 & 1553 & 154, 112, 43 & 6.56 c & 0.88 a & 6.45 c & 1.92 b \\ dippropyl trisulfide & 1713 & 1695 & 182, 43, 75 & 23.28 b & 3.32 a & 22.08 b & 5.37 a \\ ally propyl trisulfide & 1797 & 1753 & 115, 180, 73 & 0.13 b & 0.04 a & 0.10 b & 0.03 a \\ propyl \(trans\)-1-propenyl trisulfide & 1770 & 1768 & 180, 74, 116 & 5.10 c & 0.57 a & 5.90 c & 1.92 b \\ \hline \multicolumn{1}{c}{**other S-compounds**} & & & \(\Sigma\) & **6.08** & **2.45** & **9.09** & **4.83** \\ carbon disulfide & 745 & 716 & 76, 44, 32 & 0.07 b & 0.02 a & 0.03 a & 0.02 a \\
1-propanethiol & 845 & 816 & 76, 47, 43 & 0.21 a & 0.14 a & 0.84 c & 0.46 b \\
2,4-dimethylthiophene & 1197 & 1199 & 112, 111, 97 & 0.42 b & 0.16 a & 0.46 c & 0.26 a \\
3,4-dimethylthiophene & 1253 & 1264 & 112, 111, 97 & 3.57 b & 1.16 a & 5.80 b & 2.55 b \\ \(cis\)-3,5-diethyl-1,2,4-tritihalione & 1775 & 1807 & 180, 74, 151 & 0.77 c & 0.35 a & 0.84 c & 0.63 b \\ \multicolumn{1}{c}{_trans_-3,5-diethyl-1,2,4-tritihalione} & 1795 & 1826 & 180, 74, 151 & 1.04 c & 0.62 a & 1.12 c & 0.91 b \\ \hline \multicolumn{1}{c}{**aldehydes**} & & & \(\Sigma\) & **1.80** & **1.31** & **3.71** & **3.41** \\ \multicolumn{1}{c}{proposal} & 784 & 764 & 58, 29, 28 & 0.20 b & 0.11 a & 0.23 b & 0.21 b \\
2-methyl propanal & 800 & 788 & 72, 43, 41 & 0.03 a & 0.03 a & 0.03 a & 0.03 a \\
2-methyl butanal & 916 & 917 & 41, 86, 57 & 0.09 a & 0.06 c & 0.07 a & 0.07 a \\
3-methyl butanal & 914 & 921 & 44, 71, 45 & 0.36 c & 0.31 b & 0.21 a & 0.23 a \\ pentanal & 978 & 985 & 44, 86, 58 & 0.02 a & 0.02 a & 0.06 b & 0.05 b \\ hexanal & 1084  
Other S-compounds--a total of 6 S-containing VOCs other than sulfides were identified, for a total content of 6.08 mg g\({}^{-1}\) in onion flakes and 2.45 mg g\({}^{-1}\) in onion rings.