In garlic

Sulfoxides occur widely in small concentrations in plant and animal tissues, eg, aHyl vinyl sulfoxide [81898-53-5] in garlic oil and 2,2 -sulfinylbisethanol [3085-45-8] as fatty esters in the adrenal cortex (1,2). Homologous methyl sulfinyl alkyl isothiocyanates, which are represented by the formula CH3SO(CH2) NCS, where n = 3 [37791-20-1], 4 [4478-93-7], 5 [646-23-1], 8 [75272-81-0], 9 [39036-83-4], or 10 [39036-84-5], have been isolated from a number of mustard oils in which they occur as glucosides (3). Two methylsulfinyl amino acids have also been reported methionine sulfoxide [454-41-1] from cockroaches and the sulfoxide of i -methylcysteine, 3-(methylsulfinyl)alaiiine [4740-94-7]. The latter is the dominant sulfur-containing amino acid in turnips and may account in part for their characteristic odor (4). 

Allyl-propyl disulphide, (C3H5)S. S. (C3H7), exists to the extent of about 5 per cent, in garlic oil. It is a bright yellow oil of foul odour, having a specific gravity 1-023 and boiling at 66° to 69° at 16 mm. pressure. 

Naturally occurring alliin, the major precursor to the garlic aroma, is (RcSs)-( I )-,S -allyl-[.-cysteine sulfoxide 26 (Scheme 10) with both a chiral carbon and chiral sulfur - probably the first such compound (note that sulforaphene - see earlier - was isolated more or less simultaneously with alliin). Hence there are four possible stereoisomers. The alliin level in garlic is significant 5-14 mg g 1 fresh weight. 

Garlic supplements - powder tablets or capsules, steam-distilled oil, vegetable oil macerate extract, or extract aged in dilute alcohol - are widely available and are taken by millions. Since the active principle, allicin, is not present in garlic bulb, the supplements rely on the presence of precursor alliin and enzyme alliinase. In tests on 24 commercial brands of enteric-coated tablets, all except one gave low dissolution allicin release 83% of the brands released less than 15% of their potential allicin.78,79 Relevant factors were impaired enzyme activity caused by excipients and slow tablet disintegration. Caveat emptor ... 

L.D. Lawson, in Garlic The Science and Therapeutic Application of Allium sativum L. and Related Species, H.P. Koch, L.D. Lawson, Williams and Wilkins (eds), Baltimore, MD, 1996, 37-108. 

Constituents that have some known pharmacological activity that contributes to some extent to the efficacy of the product have been identified. These are known as active markers. An example of this category is alliin, which is converted to allicin in presence of allinase enzyme, and is present in garlic. These active markers may or may not have clinically proven efficacy in their own right. A minimum content or range for active markers is usually specified in pharmacopeial articles. A quantitative determination of active marker(s) during... 

The data in this paper are consistent with a wealth of evidence showing that dietary Se consumed in excess of the Recommended Dietary Allowance lowers the risk of several important cancers (2, 14, 26, 27). Previous research has established a strong association between the dietary form of Se and the cancer-preventive properties of this element (5, 28). This paper extends the evidence that Se in chemical forms known to accumulate in garlic and some Brassica species is especially effective in the prevention of chemically induced carcinogenesis (14, 17). 

Lawson LD, Ranson DK, Hughes BG. Inhibition of whole blood platelet-aggregation by compounds in garlic extracts and commercial garlic products. Thromb Res 1992 65 141-156. 

The effect of garlic on glucose homeostasis does not appear to be significant in persons with diabetes. Certain organosulfur constituents in garlic, however, have demonstrated hypoglycemic effects in nondiabetic animal models. 

The parent compound, thioacrolein, affords similar cycloadducts which are present in garlic and show potent antithrombotic activity479 480. 

The cholesterol-lowering effect of garlic was also seen in rabbits that were fed 2 g choles-terol/day for 16 weeks. A dose-dependent reduction of serum cholesterol in garlic-fed rats was observed in these experiments. 

A number of studies have focused on identifying the active antimicrobial principles in fresh garlic extract. Allicin has been identified as the active agent in garlic extracts. The antifungal activity of allicin has been shown to depend on the sulfhydryl moiety because activity is destroyed by thiols such as L-cysteine, glutathione, and mercaptoethanol. Ajoene, a compound found in oil-macerated garlic, has also been shown to have antimicrobial activity (Ali et al., 2000). 

Prasad, K. et ah, Antioxidant activity of allicin, an active principle in garlic, Mol. Cell. Biochem., 148,183-189, 1995. 

Several other spices have even better antibacterial properties than chilli. Garlic, clove, and cinnamon have chemicals that destroy the deadly bacteria Escherichia coli 0157 117. The chemicals responsible for the activity of these spices are cinnamic aldehyde in cinnamon, eugenol in clove, and diallyl thiosulfinate in garlic. The spices with the... 

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