Garlic is used as a spice because of its strong taste. It contains different constituents which imparts it strong flavour and taste along with medicinal value. It contains volatile oil, allicin (S-allyl-L-cysteine sulfoxide), S-methyl-L-cysteine sulfoxide, enzymes such as alliinase, peroxidase, and myrosinase, ajoenes (E,Z-ajoene, E,Z-methylajoene, and dimethylajoene), protein, minerals, vitamins such as thiamine, riboflavin, niacin, etc. lipids, amino acids, and others. Health preparations made of garlic were analyzed for their content of the major amino acid found, i.e. alliin and its five major decomposition products 2-vinyl-[4H]-1,3-dithiin; 3-vinyl-[4H]-1,2-dithiin; diallyl disulphide; allylmethyl disulphide and diallyl trisulphide. These constituents were found out by using two high-performance liquid chromatographic methods (1).
Diallyl disulfide is found to be the main compound in garlic oil. Other volatile compounds present include citral, geraniol, linalool, and α- and β-phellandrene. Prostaglandins were isolated from a homogenized garlic extract. High-molecular weight fructans and agglutinins were also isolated from garlic.
Composition of garlic products depends on product form. Thiosulfinates (e.g., allicin) were found to be released only from garlic cloves and garlic powder products; vinyl dithiins and ajoenes were found only in products containing garlic macerated in vegetable oil; diallyl, methyl allyl, and dimethyl sulfide series components were exclusive to products containing the oil of steam distilled garlic .