Volatile Constituents of the Distilled Oils of Welsh Onions (Allium fistulosum L. Variety Maichuon) and Scallions (Allium fistulosum L. Variety Caespitosum)

Volatile components were isolated from Welsh onions and scallions by steam distillation at atmospheric pressure and analyzed by GC and GC-MS. Sulfur-containing compounds account for 87 % and 82 % of the total volatiles in the distilled oils of Welsh onions and scallions, respectively. In addition to the sulfur compounds commonly reported in the genus Allium, 41 novel volatile sulfur-containing components were found in the distilled oils of green onions. The novel compounds can be grouped as (1) l-[alk-(en)ylthio]alkyl alk(en)yl disulfides, (2) alkyl tetra- or pentathiaalkanes or alkene(s), and (3) thiaheterocycles. Heat may be responsible for the formation of many of the sulfur-containing volatiles in green onion distilled oils. Some of the novel polysulfides identified have sweet, scallion-like or onion-like odors.