## 2 Results
### Identification of Allium Species Non-Volatile Metabolites via UPLC/PDA/qTOF-MS
#### 2.3.1. Identification of Dipeptides and Amino Acid Conjugates  
The organosulfphur dipeptides in _Allium_ are of special value considering that they are the mediators of its medicinal use and organoleptic characters. Particularly, garlic is enriched in \(\gamma\)-glutamyl peptides and sulfoxide [12]. The main organosulfphur compounds detected in garlic were \(N\)-\(\gamma\)-glutamyl-S-allycysteine, \(N\)-\(\gamma\)-glutamyl-S-allythiocysteine, allithiamine and \(N\)-hexosyl-\(N\)-\(\gamma\)-glutamyl-\(S\)-allycysteine identified in peaks L6/10, L8/15, L13, and L5.  
\(N\)-\(\gamma\)-glutamyl-\(S\)-allycysteine isomers were identified in peaks L6 and L10 (\(m/z\) 289.0873, \(\mathrm{[M-H]^{-}}\), \(\mathrm{C_{11}H_{17}N_{2}O_{5}S}\)) whereas two isomers of \(N\)-\(\gamma\)-glutamyl-S-allythiocysteine were assigned in peaks L8 and L15 (\(m/z\) 321.0612, \(\mathrm{[M-H]^{-}}\), \(\mathrm{C_{11}H_{17}N_{2}O_{5}S_{2}}\)). Lower fragment masses at \(m/z\) 128 attributed to a sequential loss of glutamine residue along the amide linkage in addition to loss of water (\(-\)18 amu) were characteristic in these dipeptides (Supplement Figure S4A,B). Additionally, a fragment appearing at \(m/z\) 249 due to the breakage of the allyl sulphur moiety was evident in peaks L8 and L15 (Figure S4B).  
Allithiamine, or thiamine allyl disulphide, a lipid-soluble form of vitamin B1 which occurs in garlic [13] was detected in peak L13 (\(m/z\) 353.0285, \(\mathrm{[M-H]^{-}}\), \(\mathrm{C_{15}H_{21}N_{4}O_{2}S_{2}}\)). Glycoside conjugate of \(N\)-\(\gamma\)-glutamyl-\(S\)-allycysteine was assigned to peak L5 (\(m/z\) 451.1401, \(\mathrm{[M-H]^{-}}\), \(\mathrm{C_{17}H_{27}O_{10}N_{2}S}\)) exhibiting the neutral loss of 162 amu for hexose moiety (Supplement Figure S4C). Similar hexose loss was detected in the two non-sulphur containing dipeptides first time reported in _Allium_ (peak L9) [\(m/z\) 421.182, \(\mathrm{[M-H]^{-}}\), \(\mathrm{C_{17}H_{29}N_{2}O_{10}}\)] and (peak L12) [\(m/z\) 455.1666, \(\mathrm{[M-H]^{-}}\), \(\mathrm{C_{20}H_{27}N_{2}O_{10}}\)] and assigned as \(N\)-hexosyl-\(\gamma\)-glutamyl-glycineucine and \(N\)-hexosyl-glutamyl-phenylalanine, respectively (Supplement Figure S4D,E). The two corresponding parent glutamine dipeptides (L7 and L11) were identified by high resolution MS with \(\mathrm{[M-H]^{-}}\) of 259.1298, and 293.1135, respectively. Lower \(m/z\) fragment ions at 128 in both peaks was attributed to glutamine loss along the amide linkage and assigned as \(N\)-hexosyl-\(\gamma\)-glutamyl-likeoleucine (L7) and \(N\)-\(\gamma\)-glutamyl-phenylalanine (L11) (Supplement  
Figure 3. Examples of natural product classes reported and detected in genus _Allium_ via UPLC/MS with selected compound(s) discussed in the manuscript. (**A**) Peptides and amino acids; (**B**) flavonoids and (**C**) fatty acids/oxylipids.  
Figure S4F,G). Loss of 80 amu for sulphate moiety was evident in an unknown peak L3 with a molecular ion of \(m/z\) 337.1711, (C\({}_{18}\)H\({}_{27}\)O\({}_{3}\)NS) (Supplement Figure S4H). A new nitrile was also tentatively annotated as a simmondisin derivative (L4) from its molecular ion at \(m/z\) 337.1711, (C\({}_{18}\)H\({}_{27}\)O\({}_{3}\)NS)\({}^{-}\). Two novel acylated peptides were detected in peaks L28 and L30 (\(m/z\) 262.1089, [M - H]\({}^{-}\), C\({}_{14}\)H\({}_{16}\)NO\({}_{4}\)) containing valine as revealed from tandem MS spectra and identified as \(N\)-\(p\)-coumaroyl-valine isomers.