Let your food be your medicine, and your medicine be your food. ...Hippocrates
Garlic preparations and their chemical compounds
Raw garlic homogenate has been the major preparation of garlic subjected to intensive scientific study, as because it is the commonest way of garlic consumption. Raw garlic homogenate is essentially same as aqueous extract of garlic, which has been used in various scientific studies. Allicin (allyl 2-propenethiosulfinate or diallyl thiosulfinate) is thought to be the principal bioactive compound present in aqueous garlic extract or raw garlic homogenate. When garlic is chopped or crushed, allinase enzyme, present in garlic, is activated and acts on alliin (present in intact garlic) to produce allicin. Other important sulfur containing compounds presents in garlic homogenate are allyl methyl thiosulfonate, 1-propenyl allyl thiosulfonate and γ-L-glutamyl-S-alkyl-L-cysteine. The adenosine concentration increases several-fold as the homogenate is incubated at room temperature. The enzyme allinase responsible for converting alliin (S-allyl cysteine sulphoxide) to allicin is inactivated by heat. Thus the water extract of heat-treated garlic contains mainly alliin. Since garlic powder is a simply dehydrated, pulverized garlic clove, the composition, especially allinase activity of garlic powder is identical to those of fresh garlic. However, dehydration temperature should not exceed 60°C, above which allinase is inactivated .Another widely studied garlic preparation is aged garlic extract (AGE). Sliced raw garlic stored in 15–20% ethanol for 20 months is refereed to as AGE. This whole process is supposed to cause considerable loss of allicin and increased activity of certain newer compounds, like S-allylcysteine (SAC), S-allylmercaptocysteine, allixin and selenium which are stable, highly bioavailable and significantly antioxidant . Another recently identified antioxidant compound of AGE is N-alpha-(1-deoxy-D-fructos-1-yl)-L-arginine (Fru-Arg) which is not present in raw or heat treated garlic .
Medicinally used garlic oil is mostly prepared by steam-distillation process. Steam-distilled garlic oil consists of the diallyl (57%), allyl methyl (37%) and dimethyl (6%) mono to hexa sulfides. A typical commercial preparation of garlic oil contains diallyl disulfide (DADS, 26%), diallyl trisulfide (DATS, 19%), allyl methyl trisulfide (15%), allyl methyl disulfide (13%), diallyl tetrasulfide (8%), allyl methyl tetrasulfide (6%), dimethyl trisulfide (3%), penta sulfide (4%) and hexa sulfide (1%). Oil-macerated garlic oil contains the vinyl-dithiins and ajoenes. Ether extracted garlic oil (essential oil) contains nine times as much of the vinyl-dithiins (5.7 mg/gm) and allyl sulfides (1.4 mg/g) and four times as much of the ajoenes (0.4 mg/g) .