## 4 Conclusions  
The research presented is the first step towards analyzing key aroma compounds in broccoli and other _Brassica_ vegetables. It showed the advantages and limitations of three important extraction techniques when they were applied to isolate volatiles from vegetables. To the best of our knowledge, it is the first attempt at broccoli volatilome analysis by the SAFE technique. There have been publications concerning SPME or SDE applications. However, one must remember that SPME is a partition-based extraction technique in which the profile of extracted compounds is highly dependent on fiber coating used. As new fiber coatings are developed, some of them dedicated to high-mass compounds or in vivo extraction, it might be possible to obtain more information on analyzed compounds due to their selectivity. For flavor studies conducted with GC-O, SPME cannot be the only method of aroma investigation, although it is the favorite for odorant target analyses due to pre-concentration capabilities.  
Three different extraction techniques were compared to evaluate their suitability for the isolation of aroma components in raw broccoli. SAFE seemed to be the most useful technique, due to the low extraction temperature and ability to extract the most compounds. SDE allowed for the isolation of numerous aroma-active components, however, the high temperature applied during the process induced artifacts formation. SPME extraction allows identification of low boiling compounds co-eluting with solvents used in other methods. The main benefit besides simplicity, rapidity and low cost is its \"green\" character. This technique does not require any toxic solvents, which is very especially relevant nowadays. Traditional key aroma determination strategies used SAFE as a basic method. This is mostly because the exhaustive extraction technique provides extracts for the flavor dilution factor (FD) determination. However, SAFE suffers from the presence of a solvent peak and problems with the analysis of low-boiling temperature compounds. For SPME analyses there is no possibility to dilute SPME extract, though some approaches use split regulation for this purpose.  
This study showed the complexity of broccoli matrix flavor and advantages and disadvantages of some of the most commonly used aroma extraction techniques. Based on the presented experiments, SAFE is a basic technique and SPME a supplementary method for these types of sample.  
The following are available online at [[http://www.mdpi.com/2304-8158/9/4/398/s1](http://www.mdpi.com/2304-8158/9/4/398/s1)]([http://www.mdpi.com/2304-8158/9/4/398/s1](http://www.mdpi.com/2304-8158/9/4/398/s1)): Figure S1: GC\(\times\)GC-ToFMS chromatograms of fresh broccoli volatiles acquired using **(A)** SAFE; **(B)** SDE and **(C)** SPME extraction techniques.  
Conceptualization, M.N.W. and H.J.; Formal analysis, H.J.; Funding acquisition, H.J.; Investigation, M.M.; Methodology, M.N.W. and M.M.; Validation, M.N.W.; Writing--original draft, M.N.W.; Writing--review and editing, H.J. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Science Centre (Poland) under Grant No. 548 2015/18/M/N2/9/00376.  
The authors declare no conflict of interest.