## 4 Conclusions  
This study deals with the characterization of two different types of dried onion, obtained by different cuts of an onion from Emilia Romagna (Italy) dried in a static oven at 40 \({}^{\circ}\)C. The flavonoid fraction was analyzed by HPLC-DAD and the volatile fraction was analyzed by both HS-SPME-GC-MS and HS-SPME-GC\(\times\)GC-TOF, with particular attention to the sulfur volatile compounds. The analysis was mainly focused on characterizing the samples and pointing out any differences in their quali-quantitative volatile and flavonoid profiles. The study also pointed out the presence of some volatile molecules never before reported in the volatile profile of dried onion samples--allyl propyl sulfide, 1-propenyl propyl sulfide, allyl isopropyl disulfide, allyl _cis_-1-propenyl disulfide, allyl _trans_-1-propenyl disulfide, 1-(1-(methylthio)propyl)-2-propyl disulfide, methyl 1-(propylthio)propyl disulfide, 1-(_cis_-1-propenylthio)propyl propyl disulfide, 1-(_cis_-1-propenylthio)propyl propyl disulfide, 1-(1-_trans_-propenylthio)propyl propyl disulfide. Some analysis, carried out in the presence of high amount of the antioxidant ascorbic acid, allowed confirming that in the volatile fraction of these dried onion samples, nonoxidized volatile _S_-compounds as thiols are absent or present in negligible amounts. To the author knowledge, this study is the first one about the use of HS-SPME-GC\(\times\)GC-TOF to deepen the characterization of the volatile fraction of dried onion samples.  
The flavonoid content was higher in onion flakes (3.56 mg g\({}^{-1}\)) than in onion rings (2.04 mg g\({}^{-1}\)). At the same time, the total content of volatile compounds was three time higher in onion flakes than in onion rings (127.26 mg g\({}^{-1}\) vs. 42.79 mg g\({}^{-1}\)), with more than 95% of this amount constituted by sulfur containing compounds. Dipropyl disulfide and dipropyl trisulfide were the most abundant VOCs, with disulfides that largely predominate the volatile fraction (about 60% on the total volatile content in onion flakes and about 77% of the total volatile content in onion rings), followed by trisulfides. HS-SPME-GC\(\times\)GC-TOF allowed detecting the presence of some molecules not detected by HS-SPME-GC-MS and provided a fast and direct visualization and comparison of different samples. These results highlight different nutraceutical properties of dried onion samples processed otherwise, only differing in shape and size, thus pointing out potentially different uses as functional ingredients.  
In light of the obtained results, highlighting different volatile and flavonoid profiles, different uses for the different parts of dried onion can be proposed by dried onion producers to the industry of food ingredients and beyond.  
The following are available online, file S1: Brief description of preliminary trials aimed at optimizing sample amount, and exposure time and temperature.  
Conceptualization, A.R., L.C.; Data curation, F.I., L.C., N.M. and P.V.; Formal analysis, L.C., F.I and P.V.; Project administration, A.R.; Resources and Supervision, A.R. and N.M.; Writing--original draft, F.I., P.V. and L.C. All authors have read and agree to the published version of the manuscript.  
This research received no external funding.  
The research was developed with the support of the Officiali Agribioenergia factory (Medicina, Bologna, Italy) and the BIOMAVO business network (Val d'Orcia, Siena, Italy). The authors are grateful for supporting the research to [PERSON] and SRA instruments (Cernusco sul Naviglio, Milan, Italy) for technical support.  
The authors declare no conflict of interest.