Onions and garlic

The compound which causes tears (the lachrymatory factor) is (Z)-propanethial-S-oxide (II) which, once the onion bulb is sliced, is derived from trans-(-h)-S-(l-propenyl)-L-cysteine sulfoxide (I) by the action of the enzyme al-liinase. Alliinase has pyridoxalphosphate as its coenzyme (cf. reaction sequence 17.11). Chopping of onions releases 3-mercapto-2-methylpentan-l-ol, which, with its very low threshold of 0.0016 pg/1 (water), smells of meat broth and onions. Raw onions contain 8-32pg/kg, and onions which have been cut, stored for 30 minutes and then cooked contain 

34-246 iLig/kg. The formation involves the attachment of H2S to the aldol condensation product of propanal and enzymatic reduction of the carbonyl group. 

AUcylthiosulfonates (III) are also responsible for the aroma of raw onions, while propyl- and propenyl disulfides (IV) and trisulfides are also supposed to play a role in the aroma of cooked onions. The aroma of fried onions is derived from dimethyl-thiophenes. 

Precursors of importance for the aroma of onions, other than compound I, are S-methyl and S-propyl-L-cysteine sulfoxide. Precursor I is biosynthesized from valine and cysteine (cf. reaction sequence 17.12). 

The key precursor for garlic aroma is S-allyl-L-cysteine sulfoxide (alliin) which, as in onions, occurs in garlic bulbs together with S-methyl-and S-propyl-compounds. The allyl and propyl-compounds are assumed to be synthesized from serine and corresponding thiols  

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SPARNINS V L, BARANY G, WATTENBERG Lw. (1988) Effects of organosulfur compounds from garlic and onions on benzo[a]pyrene-induced neoplasia and glutathione S-transferase activity in the mouse. Carcinogenesis. 9 131-4. 

NHj R = ethyl, propyl, butyl, prop-1-en-1-yl and allyl Garlic and onion -Allium sp. Components that undergo decomposition to yield lachrymators 13... 

Flighly persistent soil-living fungus that can survive for 15 years in the soil without a host plant Fall-planted garlic and onions are vulnerable in mid- to late spring when soil temperatures are ideal for the fungus. 

Allium oils are obtained from garlic and onion (Liliaceae). Their quality is assessed on the basis of their odor and aroma rather than their physical and chemical properties. The EOA specifications given below are, therefore, of limited value only. 

Antimicrobial activities of garlic and onion oil appeared to be determined by the concentrations of individual constituent sulfides. Sulfides with a single sulfur atom were not active, and sulfides with three or four sulfur atoms were highly inhibitory against the growth of Candida utilis and Staphylococcus aureus [109, 110]. 

Ernst E. Can allium vegetables prevent cancer Phytomed 1997 4 79-83. Makheja AN, Bailey JM. Antiplatelet constituents of garlic and onions. Agents Actions 1990 29 360-363. 

Block, E. The Chemistry (Sulfur Compounds) of Garlic and Onions, Sci. 

The effects of onion and garlic on eicosanoid metabolism have mainly been studied by observing the effects of garlic and onion preparations on platelet aggregation and subsequent eicosanoid synthesis. 

Ali, M., Thomson, M., and Afzal, M., Garlic and onions their effect on eicosanoid metabolism and its clinical relevance, Prostaglandins Leukot. Essent. Fatty Acids, 62, 55-73, 2000. 

These, like the isothiocyanates, are produced from precursors during cutting and cooking. While in the raw state, some members of this family - such as garlic and onion - exhibit on crushing... 

Se Speciation in Plants The presence of a number of volatile Se species was reported in edible allium plants such as garlic by GC-AES [79]. Selenomethionine, Se-methylselenocysteine, and y-glutamyl-Se-methyl-L-seleno cysteine were identibed in garlic and onion by HPLC-ICP-MS and ES-MS/MS [80]. Selenomethionine is the primary species found in all types of nuts (19D25 percent of the total Se) [30], sunBower [81], and mushrooms [36, 37], The distribution of Se among different fractions (lipid extract, low molecular weight, and protein fractions) of nuts and speciation analysis was studied [30]. Selenium was not detected in any of the lipid extracts obtained from the different types of nuts [30], Results obtained for Brazil nuts by SEC with on-line ICP-MS detection showed that approximately 12 percent of total Se was weakly bound to proteins [30],... 

Se-enriched plants may be divided into two broad groups [199], i.e. selenium accumulators and/or selenium non-accumulators. Selenium-accumulating plants can be divided into three subgroups selenite-accumulators (broccoli and cucumber), selenomethionine accumulators (grains such as wheat, and mushrooms) and iS e-methyl selenomethionine accumulators (garlic and onion) [200]. 

Ali M, Bordia T, Mustafa T.Effect of raw versus boiled aqueous extract of garlic and onion on platelet aggregation. Prostagland Leukot Essen Fatty Acids 1999 60(1) 43— 47. 

Makheja, A.N. and Bailey, J.M. (1990) Antiplatelet constituents of garlic and onion. Agents Actions. 29 360-363. 

Organic sulphur compounds usually play a considerable role in the sensory characteristics of food and beverages, as they are frequently contributors to the character of impact-scents. Examples of these products include truffle (Diaz et al., 2003 Aprea et al., 2007), garlic and onion (Yan et al., 1993 Bocchini et al., 2001), cooked meat (Hinrichsen and Pedersen, 1995 Andres et al., 2002 Carrapiso et al., 2002), coffee (Shimoda and Shibamoto, 1990 Semmelroch and Grosch, 1996), fruit juices (Winter et al., 1976 Boelens and van Gement, 1993 Hinterholzer... 

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