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.