Sulfides onion

Dimethyl sulfoxide occurs widely at levels of <3 ppm. It has been isolated from spearmint oil, com, barley, malt, alfalfa, beets, cabbage, cucumbers, oats, onion, Swiss chard, tomatoes, raspberries, beer, coffee, milk, and tea (5). It is a common constituent of natural waters, and it occurs in seawater in the 2one of light penetration where it may represent a product of algal metaboHsm (6). Its occurrence in rainwater may result from oxidation of atmospheric dimethyl sulfide, which occurs as part of the natural transfer of sulfur of biological origin (7,8). 

Nishimura and coworkers57-59 studied the y-radiolysis of aqueous solutions of sulfoxide amino acids. Sulfoxide amino acids are the precursors of the flavors of onions (S-propyl-L-cysteine sulfoxide, S-methyl-L-cysteine sulfoxide and S-(l-propenyl)-L-cysteine sulfoxide) and garlic (S-allyl-L-cysteine sulfoxide). In studies on sprout inhibition of onion by /-irradiation it was found that the characteristic flavor of onions became milder. In the y-radiolysis of an aqueous solution of S-propyl-L-cysteine sulfoxide (PCSO)57,58 they identified as the main products alanine, cysteic acid, dipropyl disulfide and dipropyl sulfide. In the radiolysis of S-allyl-L-cysteine sulfoxide (ACSO) they found that the main products are S-allyl-L-cysteine, cysteic acid, cystine, allyl alcohol, propyl allyl sulfide and diallyl sulfide. The mechanisms of formation of the products were partly elucidated by the study of the radiolysis in the presence of N20 and Br- as eaq - and OH radicals scavengers, respectively. 

Let us note in addition that the layered sulfides M0S2 and WS2 have been found to form nanotubes and other fullerene-type structures, on account of their highly folded and distorted nature that favors the formation of rag and tubular structures. Such materials have been synthesized by a variety of methods [78] and exhibit morphologies, which were described as inorganic fiillerenes (IF), single sheets, folded sheets, nanocrystals, and nested IFs (also known as onion crystals or Russian dolls ). 

It has also been reported that some products with distinct flavors can be successfully contained in fluorinated container13-15 Work done at the AEC on the containment of concentrated flavorants in HDPE containers showed excellent containment for butter LR12390, aniseed oil, and dimethyl sulfide. The unacceptable barrier properties found for OR onion, OR garlic, and banana LR4186 led to a massive slump in popularity of one of the authors from colleagues who accused him of poisoning them ... 

A number of volatile aliphatic compounds that contain nitrogen or sulfur atoms are important aroma constituents. Alkyl thiols, dialkyl sulfides and disulfides, and alkyl thiocyanates belong to this group. They occur widely in foods and spices and determine the odor of, for example, onions, garlic, and mustard. Because of their potent smell, they are used in high dilution and are often produced only in small quantities. The same is true for the following ... 

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]. 

Also heterocyclic flavour molecules can be formed from renewable resources. 3,5-Diethyl-1,2,4-trithiolane is an important molecule for onion flavours and can easily be prepared from propanal obtained by biotransformation and hydrogen sulflde (Scheme 13.17). A meat flavour molecule like thialdine [dihydro-2,4,6-trimethyl-l,3,5(4H)-dithiazine] can be prepared from acetaldehyde isolated from molasses and ammonium sulflde (Scheme 13.18). The bacon flavour substance 2,4,6-triisobutyl-5,6-dihydro-4H-l,3,5-dithiazine can be prepared from isovaleraldehyde prepared from essential oils and ammonium sulfide (Scheme 13.19). 

This important flavor compound was identified in the head-space volatiles of beef broth by Brinkman, et al. (43) and although it has the odor of fresh onions, it is believed to contribute to the flavor of meat. This compound can be formed quite easily from Strecker degradation products. Schutte and Koenders (49) concluded that the most probable precursors for its formation were etha-nal, methanethiol and hydrogen sulfide. As shown in Figure 5, these immediate precursors are generated from alanine, methionine and cysteine in the presence of a Strecker degradation dicarbonyl compound such as pyruvaldehyde. These same precursors could also interact under similar conditions to give dimethyl disulfide and 3,5-dimethyl-l,2,4-trithiolane previously discussed. 

Allylic sulfides May stimulate production of protective enzymes Garlic, onions... 

Garlic, Allium sativum L., is a species in the onion family, Alliaceae. Onion, shallot, and leek are close relatives. Garlic has been used throughout history for both culinary and medicinal purposes. It has a pungent hot sensation that mellows and sweetens considerably with cooking. A large number of sulfur compounds contribute to the smell and taste of members of the onion family. Diallyl disulfide and diallyl sulfide are... 

Alkyl sulfides and thiols. Some alkyl thiols and sulfides, notably those from commonly ingested Allium sativum (garlic) and Allium cepa (onion) (Alliaceae), are variously bioactive as odorants and antimicrobials. Propanethial S-oxide (CH3-CH2-CH=S=0) is a lachrymatory irritant principle of onion. Allicin (S-oxodiallydisulfide CH2=CH—CH2-SO-S-CH2— CH=CH2), diallyldisulfide (CH2=CH-CH2-S-S-CH2-CH=CH2) and diallylsulfide (CH2=CH—CH2—S—CH2-CH=CH2) are major odorants of garlic that are reactive and irritant because of the allyl groups. Dimethyl disulfide (CH3—S—S-CH3), dipropyl disulfide (CH3-CH2-CH2-S-S-CH2-CH2-CH3), methyl allyl disulfide (CH3-S-S-CH2-CH=CH2) and propane-1-thiol (CH3-CH2—CH2—SH) are further Allium odorants. Methane thiol (methyl mercaptan CH3—SH) is a widespread plant volatile and notably derives from anaerobic bacterial degradation of cysteine as in human flatus and bad mouth odour. The aliphatic disulfides allicin and ajoene inhibit proinflammatory expression of iNOS. 

Allyl methyl trisulfide (alkene sulfide) Allium cepa (onion), A. sativum (garlic) (Liliaceae) [bulb] SLOX (competitive)... 

Sulfides and Thiols, acyclic 7 Mercaptan, methylthioethane meaty (1-5 ppb), onion... 

Tests on a number of these small units revealed that the ozone concentration in the room was less than 0.01 p.p.m. by weight. There is ample evidence that various food odors, such as from fish, onions, acrolin from burnt fat, and tobacco as well as body odors can be oxidized by ozone. This is substantiated by many reports in the literature (4,13-15j 30y SI). Tests made in the laboratory with various unsaturated organic compounds such as indole and skatole (fecal odor), allyl sulfide (garlic odor), and methyl thiocyanate (unpleasant odor of almonds) showed them to be readily oxidized, as evidenced by lack of odor. Saturated compounds such as butyric and valeric acids were not oxidized under the same conditions. Special fixures with ultraviolet lamps producing a controlled amount of ozone are used in animal hospitals and kennels for prevention of cross infection and for the oxidation of animal and fecal odors. 

Several thiols occur naturally for example, skunk secretion contains 3-methyll-butanethiol and cut onions evolve 1-propanethiol, and the thiol group of the natural amino acid cysteine plays a vital role in the biochemistry of proteins and enzymes (see Introduction, p. 2). Primary and secondary thiols may be prepared from alkyl halides (RX) by reaction with excess sodium thiolate (SN2 nucleophilic substitution by HST) or via the Grignard reagent and reaction with sulfur. Tertiary thiols can be obtained in good yields by addition of hydrogen sulfide to a suitable alkene. Thiols can also be prepared by reduction of sulfonyl chlorides (Scheme l).la,2a... 

Thiols or alkyl hydrogen sulfides are sulfur analogues of alcohols and sulfides are sulfur analogues of ethers. Many of the lower molecular weight examples have strong odors and are naturally found in onions, garlic, and the spray of skunks. 

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