## 2 Results
### Identification of Volatiles
#### 2.1.1. Concentrations of Isothiocyanates and Nitriles in Raw and Cooked _Brassica_ Vegetables  
Very small amounts of isothi cyanates were detected in all of the raw broccoli cultivars (<2% in all samples). Additionally, the nitrile levels were relatively low (<5%), which confirms very low concentrations of myrosinase hydrolysis products in the gas phase. The diversity of isothi cyanates was also very limited, barely four different isothi cyanates were identified using GC\(\times\)GC. Both 2-methylbutyl isothi cyanate and isobutyl isothi cyanate were found in the cultivars Malibu and \"2970\", while cyclopentyl isothi cyanate and n-hexyl isothi cyanate were present in all the analyzed broccoli samples. The composition of isothi cyanates was different in cooked vegetables, as propane, 1-isothiocyanato-, butane, 1-isothiocyanato-, 1-butene, 4-isothiocyanato- and benzene, (2-isothiocyanatoethyl)- were detected in all the analyzed cooked vegetables, instead of most isothi cyanates present in raw vegetables. The most interesting result was found in the cooked cultivar \"2970\", where all the described isothiocyanates were present, along with a significant amount of allyl isothi cyanate (which was not present in the raw broccoli). This unexpected finding was connected with the absence of sulforaphene, one of the most explored isothi cyanates present in broccoli. Because of the health benefits of sulforaphene [6], interest in this component concentration is particularly high. Solvent assistant flavor evaporation (SAFE) extraction was performed for one broccoli cultivar to check if the sulforaphene was present in the sample. In the SAFE extract, analyzed by GC\(\times\)GC-ToFMS,  
Figure 2: Percentage contents of isothi cyanates, alcohols, aldehydes, other sulfur compounds, nitriles, others (miscellaneous) in all analyzed samples. Broccoli (**a**): Covina, Malibu, “2970”; Brussels sprouts (**b**): Ajax, Marte, Maximus, Neptuno, Profitus; Cauliflower (**c**): Charlotte, Liria, Oviedo; Kohlrabi (**d**): Kolibri, Konan, Konmar, Kordial. sulforaphane and also sulforaphane nitrile were present as glucoraphanin degradation products, although in very small concentrations. The absence of sulforaphane in the SPME extract may either be due to the labile nature of this component [19], or more probably, due to its small K value (partition coefficient sample-headspace-fiber). SAFE is an exhaustive extraction type technique, therefore other/more components can be identified. The concentration and diversity of isothiyanates was much greater in the cooked broccoli. The amounts were almost two times higher than in the raw vegetables. It was reported that myxosinase in the broccoli matrix is inactivated after 20 min at 60 \({}^{\circ}\)C [20]. No reports have been found in available literature on the stability of nitrile specific proteins. Generally, the total amount of glucosinolate degradation products decreased, especially the concentration of nitriles. Cooking caused a change in the amount of isothiyanates, which is beneficial from the consumer's point of view. In cauliflower, the major isothiyanate was allyl isothiyanate, representing 2-4% of the total volatile fraction, resulting from the high concentration of sinigrin, its precursor, in cauliflowers [12]. Allyl isothiyanates are some of most frequently studied isothiyanates, with many publications confirming their anticancer activity in both cultured cancer cells and animal models. Moreover, the bioavailability of this compound is very high, as almost 90% of oral intake is absorbed [21]. Other isothiyanates were also present, although in much lower concentrations, usually less than 1%. In the Lira and Charlotte cultivars, somewhat higher amounts of isothiyanates were recorded in the cooked vegetables compared with the raw vegetables, while in the Oviedo cultivar the situation is opposite. An abundant group in all raw cauliflower cultivars was composed of nitriles, which constituted almost 10% in all analyzed samples.