Distribution of Eleven Flavor Precursors, S-Alk(en)yl-L-Cysteine Derivatives, in Seven Allium Vegetables

Using high-performance liquid chromatography, 11 sulfur-containing flavor precursors were determined quantitatively in seven Allium vegetables: garlic (Allium sativum), onion (A. cepa), Welsh onion (A. fistulosum), Chinese chive (A. tuberosum Rotter), rakkyo (A. chinense G. Don), ‘asatsuki’ (A. schoenoprasum), and leek (A. porrum). The determinants were S-alk(en)yl-L-cysteine derivatives, methiin, alliin, isoalliin, cycloalliin, deoxyalliin, N-(γ-glutamyl)-S-methyl-L-cysteine, N-(γ-glutamyl)-S-(2-propenyl)-L-cysteine, N-(γ-glutamyl)-S-(E-1-propenyl)-L-cysteine (Glu-PEC), N-(γ-glutamyl)-S-(2-propenyl)-L-cysteine sulfoxide, N-(γ-glutamyl)-S-(E-1-propenyl)-L-cysteine sulfoxide (Glu-PECSO) and S-(2-carboxy-propyl) glutathione. The constituents of the flavor precursors, methiin, alliin and isoalliin, were compared among the seven Allium vegetables. Molar ratios of methiin/alliin/isoalliin (M/A/I, %) were similar in onion (16/0/84), Welsh onion (19/0/81), asatsuki (11/0/89), and leek (19/0/81). Garlic, Chinese chive and rakkyo showed specific ratios of 17/78/5, 80/13/7 and 68/0/32, respectively. The storage compounds of isoalliin, a major flavor precursor that is common among seven Allium vegetables, were Glu-PEC in garlic and Glu-PECSO in onion.