Methional formation

The mechanism of the formation of oxidizing species as determined by the effects of specific inhibitors have varied. In suspensions of both phagocytosing PMNs and of granules derived therefrom ethylene was produced from methional or from... 

The data with the spin trap DMPO were very similar to those of Tauber et al. 127, ns) measuring the formation of ethylene from methional or KMB. Unfortunately, as with the use of oxidizable organic molecules, the specificity for OH of the spin adduct identified in the experiments with ESR is not clear. A critical, cautionary review of this approach has recently appeared... 

Moreover, the oxidation of methional to ethylene has been proposed (Beauchamp and Fridovich 1970 Biaglow et al. 1997), and the formation of allantoin (Grootveld and Halliwell 1987 Halliwell et al. 1988) from uric acid as well as the imidazolone derivative from histamine (Ching et al. 1995) have been suggested as an index of OH action in vivo (Halliwell et al. 1988). 

Coffee (Arabica) /3-Damascenone, 2-furylmethanethiol, 3-sulfanyl-3-methylbutyl formate (126), homofuronol (127), furaneol, guaiacol, 4-vinylguaiacol, methional, sotolone, 2-ethyl-3,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, vanillin, 4-ethylguaiacol, homosotolone (128) 147... 

Methionine sulfoxide formation may occur without noticeable changes in physical or immunochemical properties of the protein. Thus reduction of sulfoxide to thioether often completely restores the lost protein function. Many cells, including human polymoprhonuclear neutrophilic leukocytes, contain enzyme methionine sulfoxide reductase, which is able to convert methionine sulfoxide to the reduced methione form in a variety of proteins (B25, F8). Methionine reacting with a strong oxidant effects methionine sulfone production, which in vivo is not reduced back to methionine. 

One of the most interesting papers on ascorbic acid-Cu reactions showed that ascorbic acid-Cu catalyzes the formation of ethylene from several precursors. The interest in ethylene was as an abscission agent in plants. All alcohols, aldehydes, acids, ethers, and epoxides formed ethylene when mixed with Cu and ascorbic acid in 5-mL closed bottles at 30 °C for 1 h. Methional was the most active, followed by propanal, propanol, propyl ether, ethyl ether, and ethanol. This reaction may be part of the oxygen scavenging system because Cu increases ascorbic acid s ability to scavenge oxygen. The authors claim this reaction cannot be attributed to copper in its lower valence state. 

Methional results from a Strecker degradation of methionine. It is at the origin of formation of methanethiol (Q.2), dimethyl disulfide (Q.14) and acrolein (C.16). 

The mechanism accounting for the formation of ethylene from methional consists of electron transfer from the sulfur atom of methional to the pho-toactivated FMN (FMN ), followed by a nucleophilic attack by OH on the aldehyde group and a concerted elimination of the methylsulfinium group ... 

Employing electron paramagnetic resonance (epr) spectroscopy, Bors et al. (1976) verified formation of the methional sulhnium radical as an intermediate but suggested that the reaction mechanism for the oxidation of methional to ethylene was more complex than a simple fragmentation reaction. More recently Pryor and Tang (1978) found that a variety of organic radicals also led to the production of ethylene from methional and cautioned that this reaction could not be used as evidence for the presence of HO- radicals. 

Kinetics of the Formation of Methional, Dimethyl Disulfide, and 2-Acetylthiophene via the Maillard Reaction... 

Strecker aldehydes are quantitatively the major products of the Maillard reaction. In addition to their intrinsic flavor, they are very reactive and participate in numerous reactions that make additional contributions to flavor development in foods. There is a lack of information on the reaction kinetics of these Strecker aldehydes as well as other flavor compounds. Thus a kinetic study on the formation of methional and two secondary products (dimethyl disulfide and 2-acetylthiophene) from the reaction of amino acids (0.075 mole) and glucose (0.5 mole) in aqueous model systems was conducted. Systems were heated at temperatures from 75 to 115°C at times from 5 min. to 7.5 h and pH s of 6, 7, and 8. Kinetic data are presented and discussed. 

The Macintosh program "Water Analyzer Series - Reaction Kinetics Program V. 2.09" (13) was used to do kinetic analysis of the data. The reaction order for the compounds selected (dimethyl disulfide, methional, and 2-acetylthiophene) were determined by plotting concentration versus time and then using linear regression to determine how well the data fit the straight line. The r for all three compounds at zero order ranged form 0.83 to 0.99 and were consistently better than any other order. It was, therefore, concluded that the formation of dimethyl disulfide, methional, and 2-acetylthiophene all followed zero order reaction kinetics. 

Figure 2. The influence of heating time and pH on the formation of methional at 95°C.

A final mechanism for the formation of carbonys via nticroorganisms involves the transamination and decarboxylation of free amino acids. Morgan [95] has demonstrated the production of 3-methyl butanal by S. lactis var. maltigenes (Figure 5.10). MacLeod and Morgan [96] have demonstrated the production of 2-methyl butanal, methional and phenylacetaldehyde from leucine, methionine and phenylalanine, respectively, by the same microorganism. 

Chan, R, G.A. Reineccius, Kinetics of the formation of methional, dimethyl disulfide, and 2-acetylthiophene via the MaiUard reaction, in Sulfur Compounds in Foods, M.E. Keenen. C.J. Mussinan, Eds., Amer. Chem. Soc., Washington, D.C., 1994, p. 127. Zheng, Y., C.-T. Ho, Kinetics of the release of hydrogen sulfide from cysteine and glutathione during thermal treatment, in Sulfur Compounds in Foods, M.E. Keenen. C.J. Mussinan, Eds., Amer. Chem. Soc., Washington, D.C., 1994, p. 138. 

In tomato paste, for example (cf. Table 17.12), it was found that the changes in aroma caused by heating are primarily due to the formation of dimethylsulfide, methional, the furanones HD2F and HD3F and the increase in P-damascenone, and a substantial decrease in (Z)-3-hexenal and hexanal. 

Significant aliphatic sulfur compounds are methional, 3-methyl-but-2-ene-1-thiol, 3-mercapto-3-methylbutan-l-ol (8-124), its ester 3-mercapto-3-methylbutyl formate, methanethiol and dimethyltrisulfide. 3-Mercapto-3-methyl-l-ol also occurs in passion fruit and blackcurrant, and as a putative cat pheromone in cat urine, where it is formed as a degradation product of amino acid L-felinine (see Section 2.2.1.2.2). Of more than 70 known pyrazines, the most important compounds in roasted coffee are isopropylpyrazine, 2-isobutyl-3-methoxypyrazine, 2-ethyl-3,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, 2,6-dimethyl-3-vinylpyrazine and 2-ethyl-6-methyl-3-vinylpyrazine. Pyridine and its alkyl derivatives and bicyclic pyridines have a negative impact on the quality of coffee aroma. Important aromatic... 

Methionine and riboflavin are useful nutrients in foods, especially, dairy products. However, during light irradiation, methionine is well-known to produce sulfur ofF-odorants due to the participation of photosensitized riboflavin under neutral conditions. In this study, the important sulfur off-odorants were found to be methional, dimethyl disulfide, and dimethyl trisulfide, formed from methionine and riboflavin under acidic conditions during light irradiation. The inhibition effect of a variety of antioxidants on the formation of the ofF-odorants has also been studied. 

Figure 2 shows that part of the antioxidants accelerated the formation of DMTS, however, most antioxidants inhibited the formation of all the sulfur compounds. Especially, the addition of catechin derivatives, that is (-)-epicatechin, (-)-epigallocatechin, (-)-epigallocatechin gallate, and rosmarinic acid were found to decrease the amounts of methional, DMDS, and DMTS at... 

Methional has been reported to be the most important off-odorant in the system of riboflavin and methionine under neutral conditions with light irradiation, however, under acidic conditions, dimethyl disulfide and dimethyl trisulfide in addition to methional were also the characteristic off-odorants. Most of the antioxidants used were found to be effective inhibitors of the formation of the sulfur off-odorants. Especilally, the catechin derivatives and rosmarinic acid were available. The scavenging ability of the antioxidant against the free radical seems to be related to the formation amount of methional, dimethyl disulfide, and dimethyl trisulfide. In addition to the radical species, singlet oxygen was also suggested to participate in the formation of dimethyl disulfide and dimethyl trisulfide from methionine and photosensitized riboflavin under acidic conditions. 

Strecker aldehydes are a frequent source of off-flavors in fermented products. Development of off-flavors in oxidized white wines typically marks the end of shelf life. Methional (3-methylthiopropionaldehyde) was identified as producing a cooked vegetables off-flavor character in a young white wine that had undergone spontaneous oxidation (101). Methional levels increased in wines spiked with methionol or methionine, suggesting its formation via direct peroxidation or Strecker degradation of methionine. Methional was recently demon-... 

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