Figure 2.

Bioactive sulfur compounds in Allium vegetables. S-alk(en)yl-L-cysteine sulfoxides (ASCOs) are the precursors to the biologically active compounds in Allium vegetables. ASCOs are formed form γ-glutamyl-S-alk(en)yl-L-cysteines in the vegetables cells. When the vegetables are crushed, chopped, or chewed, the enzyme alliinase is released from vacuoles and catalyzes the conversion of ASCOs to highly reactive sulfenic acid intermediates. Thiosulfinate compounds are formed from the condensation of these intermediates. Thiosulfinate compounds and their metabolites are responsible for the characteristic flavors and odors of Allium vegetables. Predominant compounds of ASCOs and thiosulfinate compounds/metabolites in garlic and onions are listed. See text for citations of references.