Garlic Chemistry: Chemical and Biological Properties of Sulfur-Containing Compounds Derived from Garlic

Garlic (Allium sativum L.) is rich in biologically active organosulfur compounds. Although intact garlic cloves contain a limited number of organosulfur compounds, such as alliin, methiin and γ-glutamyl-S-alk(en)yl-cysteines, processing initiates a cascade of chemical transformation reactions. Allicin is one of the well-known transformation compound, however, it is highly unstable and reactive, and quickly decomposes into other organosulfur compounds including alk(en)ly-polysulfides, ajoenes and vinyldithiins. Thus, allicin is a transient compound and likely only its transformation compounds contribute to the health benefits of garlic. Recently, biological activities of water-soluble organosulfur compounds derived from garlic, such as S-allyl-L-cysteine and S-allylmercapto-L-cysteine, have become the center of attention because they are stable, odorless and safe. Studies on structure-activity relationships have revealed that the S-allyl group plays an important role in the pharmacological activities of organosulfur compounds derived from garlic. Further, consumption of garlic shows feasibility to prevent cancer and affect immunomodulation or enhancement of the immune systems.