Sulfur compounds formed from dimethyl disulfide

The edible portion of broccoli Brassica oleracea var. italica) is the inflorescence, and it is normally eaten cooked, with the main meal. Over 40 volatile compounds have been identified from raw or cooked broccoli. The most influential aroma compounds found in broccoli are sulfides, isothiocyanates, aliphatic aldehydes, alcohols and aromatic compounds [35, 166-169]. Broccoli is mainly characterised by sulfurous aroma compounds, which are formed from gluco-sinolates and amino acid precursors (Sects. 7.2.2, 7.2.3) [170-173]. The strong off-odours produced by broccoli have mainly been associated with volatile sulfur compounds, such as methanethiol, hydrogen sulfide, dimethyl disulfide and trimethyl disulfide [169,171, 174, 175]. Other volatile compounds that also have been reported as important to broccoli aroma and odour are dimethyl sulfide, hexanal, (Z)-3-hexen-l-ol, nonanal, ethanol, methyl thiocyanate, butyl isothiocyanate, 2-methylbutyl isothiocyanate and 3-isopropyl-2-methoxypyrazine... 

Group 3 volatiles, formed by further interactions, can reach even lower threshold values than those mentioned so far, particularly when sulfur is involved, usually derived by the break down of cysteine (bis(2-methyl-3-furyl) disulfide, 0.00002 2-methyl-3-furanthiol, 0.0004 2-furylmethanethiol, 0.005 dimethyl trisulfide, 0.01 dimethyl disulfide, 0.16 dimethyl sulfide, 0.3 hydrogen sulfide, 10). Into some volatile sulfur compounds other atoms as well as the sulfur of cysteine are incorporated (2-acetylthiazoline, 1 5-acetyl-2,3-dihydro-l,4-thiazine, 1.25 2-acetylthiazole, 10). Other volatiles are more likely to be derived from methionine (methanethiol, 0.2). 

The rapid development of chiral phosphine derivatives of ferrocene was undoubtedly due to their application in catalysis. In contrast, chiral sulfur compounds from lithiated iV,iV-dimethyl-l-ferrocenylethylamine were only prepared about 15 years later [140], For the synthesis of such derivatives, the lithiated amine is treated with disulfides as shown in Fig. 4-24, top (and analogously, diselenides [141]). The sulfides obtained are easily oxidized by peracids or NaI04 to the corresponding sulfoxides. As sulfur becomes a new center of chirality by the oxidation, diastereoisomeric sulfoxides are formed in ratios depending on the oxidant [140]. If chiral oxaziridines [106, 142] are used as oxidizing agents, the diastereoisomeric ratio is appreciably... 

Methanethiol-related volatile sulfur compounds are derived from methyl methanethiosulfinate via nonenzymic chemical reactions. Methanethiol and dimethyl trisulfide are readily formed in a model system composed of methyl methanethiosulfinate and hydrogen sulfide (Figure 3 21,22) which is also a volatile component in disrupted tissues of cruciferous vegetables (4,5,17). Additionally, dimethyl disulfide has also been shown to be formed facilely from methyl... 

Alkaline and acidic solutions were employed in the experiment because Marks et al. (20) reported that the formation of -methyl-L-cysteine sulfoxide breakdown products was dependent on pH of the vegetable tissues. Table YU shows that the alkaline treatment had the most pronounced effect among the treatments on suppressing the formation of dimethyl disulfide which appears to contribute strongly to the unpleasant volatile sulfur compound aroma in stored broccoli. This effect probably results from the destruction of methyl methanethiosulfinate by the hydroxide ion (33). Thus, strategies for suppressing undesirable volatile sulfur compounds in cruciferous vegetables and other foods need to incorporate means to minimize contributions by oxidized forms of methanethiol as well as methanethiol itself. 

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