The Evidence for the Production Mechanism of cis-S-1-Propenylcysteine in Aged Garlic Extract Based on a Model Reaction Approach Using Its Isomers and Deuterated Solvents

cis - S -1-Propenylcysteine has been identified in aged garlic extract, however, its production mechanism is still unclear. The content of cis - S -1-propenylcysteine in aged garlic extract at 22 months of aging was more than twice the molarity of γ -glutamyl- cis - S -1-propenylcysteine in raw garlic, a plausible precursor of cis - S -1-propenylcysteine. We found that cis - S -1-propenylcysteine was generated through the isomerization of trans - S -1-propenylcysteine in the model reactions. These results suggested that the isomerization was induced by the electron-releasing conjugative effect of the sulfur atom in S -1-propenylcysteine.