Allicin and Related Organosulfur Compounds of Garlic (Allium sativum L.): Chemistry, Separation, Quantitative Determination and Applications

Garlic (Allium sativum L.) owes its pungency, odour and most of its attributed bioactivity to a single reaction system: the conversion of the odourless precursor alliin into the thiosulfinate allicin when tissue is disrupted. Because allicin is absent from the intact clove, unstable in aqueous and thiol-containing media, and undetectable in plasma after consumption, the composition of any garlic preparation is governed by its processing history, and the electrophilicity of the thiosulfinate group determines which products survive. The review is organised around the alliin–alliinase–allicin system, not the plant itself. A measured allicin value is defined by the method that produced it. Extraction strategy, quantification platform, validation and reporting basis set the result as much as the sample does. Measured allicin must be distinguished from allicin potential. Assessed against the requirement of chemical definition, the reported biological, agricultural, food-preservation and nanomaterial applications rest on largely preclinical evidence, and often on materials never chemically characterised. The principal obstacle to comparability is the absence of a harmonised reference procedure for allicin quantification, not a shortage of biological observations. This review identifies the analytical and processing advances required to convert garlic from a raw commodity into reproducible, standardised ingredients.