## 3 Results and Discussion
### Evaluation of SAFE, SDE and SPME Extracts by GC\(\times\)GC  
All extracts were analyzed by GC\(\times\)GC-ToFMS (Figure S1 in supplemental materials) and the results are shown in Table 2. The analysis was performed in order to compare volatile profiles among different samples. Those results were also useful in identification of aroma-active components in Table 1. The use of SDE, SAFE and SPME allowed for the identification of 120 volatile compounds extracted from fresh broccoli. All of them were identified tentatively by comparison with NIST spectra after deconvolution using Chromat 4.40 software. Compounds with the probability of \(>\)700 were listed in the table along with their molecular masses. All extraction techniques gave a majority of alcohols, which consist of at least 40% of all chemical groups extracted (Figure 1). The second most abundant fraction was sulfur components (mainly sulfides). The meaningful differences between extraction techniques were observed in pyrazines and furans concentration. Pyrazines are present almost exclusively in the SDE extract; however, it is worth highlighting that the aroma of pyrazines (green peas, etc. ), observed in GC-O analysis is present in all samples (see Table 1). On chromatograms, the pyrazines are visible only in SDE extracts, which clearly indicates that despite all the disadvantages of this technique it might be helpful for the identification of some compounds not visible in milder techniques (SAFE, SPME). There is also a high concentration of furans in SPME and SDE extracts. SPME is specifically important for the determination of early eluting compounds, like methanethiol, dimethyl sulfide etc., which coelute with the solvent and, therefore, is not visible with solvent delay in splitless injections. Sulforaphan a bioactive molecule with proven positive health benefits that was present only in the SAFE extract, probably caused by the non-stable nature of this compound. SDE applied high temperature, which might lead to its destruction, while in SPME it might be extraction temperature, extraction time, or most likely the low value of distribution constant that influences the migration of compounds to headspace. It is worth noting the proportion between sulfides in particular extracts. The percentage of dimethyl disulfide is definitely higher in SPME than in the two other methods. Dimethyl trisulfide is on a similar level in all analytes, however the percentage is slightly higher in SPME (Table 2). Dimethyl tetrasulfide is present in very low concentrations in SPME compared with SDE and SAFE. Dimethyl pentasulfide is not present in SPME extracts, while it is relatively high at 3.6% in the SDE extract and at 0.4% in the SAFE extract. The absence of high molecular sulfides in the SPME extract might be caused by their low Henry's constant and molecular weight, as SPME is more suitable for low molecular weight compounds isolation. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Compound** & **Molecular Weight** & **SDE \%** & **SAFE \%** & **SPME \%** \\ \hline methanethiol & 48 & S & s & 0.26 \\ ethanentirle & 55 & S & s & 0.26 \\ dimethyl sulfide & 62 & S & s & 2.42 \\
1,3-pentadiene, (E)- & 68 & 0.76 & 0.03 & nd \\
1,3-pentadiene, (Z)- & 68 & 0.80 & nd & nd \\
1,4-pentadiene & 68 & 0.13 & nd & 0.03 \\ butanentirle & 69 & 0.61 & nd & nd \\ thiocyanic acid, methyl ester & 73 & 2.30 & 1.12 & 4.38 \\
1-butanol & 74 & 0.32 & 0.04 & nd \\ methyl ethyl sulfide & 76 & nd & nd & 0.02 \\ dimethyl sulfoxide & 78 & 2.93 & 5.38 & 0.04 \\ pyrazine & 80 & 0.28 & nd & nd \\
2-pentenitrile & 81 & 0.18 & nd & nd \\ methylyl cyanide & 81 & nd & 0.05 & nd \\ furan, 2-methyl & 82 & s & s & 0.06 \\ butanentirle, 3-methyl- & 83 & 0.47 & nd & nd \\
1-penten-3-one & 84 & 0.55 & 0.85 & 0.73 \\
2-pentenal, (E)- & 84 & 0.67 & 1.20 & 0.26 \\
1-penten-3-ol & 86 & 4.84 & 9.31 & 10.01 \\
2-penten-1-ol. (E)- & 86 & 11.86 & 14.34 & 10.03 \\ butanal, 2-methyl- & 86 & nd & 0.51 & nd \\ pentanal & 86 & 0.38 & 1.52 & nd \\ \hline \hline \end{tabular}
\end{table}