Methional

Other examples are glycine — formaldehyde, alanine — acetaldehyde, valine — isobutyraldehyde, phenylalanine — phenylacetaldehyde, and methionine — methional (106). Products such as dried skim milk, dried eggs, and dehydrated vegetables and fmits are particularly susceptible to deteriorative flavor changes ascribed to this reaction (Table 10). 

AEyl chloride reacts with sodamide in Hquid ammonia to produce benzene when sodamide is in excess, hexadiene dimer is the principal product, with some trimer and tetramer (C24, six double bonds). AEylation at carbon atoms alpha to polar groups is used in the preparation of a-aEyl-substituted ketones and nittiles. Preparation of P-diketone derivatives, methionic acid derivatives, and malonic ester, cyanoacetic ester, and P-keto-ester derivatives, etc, involving substitution on an alpha carbon between two polar carbonyl groups, is particularly facEe. 

DMDS, DMTS, MT, methional, hexanethiol and thiophene 2-aldehyde. H2S and COS also make a contribution.33... 

In soft cheeses, such as Brie, Camembert, and Limburger, the following sulfur compounds were implicated 3-(methylthio)propanol, MT, DMS, DMDS, DMTS, dimethyl tetrasulfide, methyl ethyl disulfide, diethyl disulfide, 2,4-dithiapentane, 3-methylthio-2,4-dithiapentane, methional, 2,4,5-trithiahex-ane, 1,1-fe-methylmercaptodisulfide, methyl thioacetate (=methanethiol acetate), benzothiazole, methylthiobenzothiazole, methyl ethyl sulfonate, methyl methane thiosulfonate, thiophene 2-aldehyde, and H2S.34 Many of these were only present in small amounts Limburger cheese was notable for 13.2% of DMDS, 0.5% of methyl thioacetate, and 0.8% of DMTS. 

Iron complexes or microsomal nonheme iron are undoubtedly obligatory components in the microsomal oxidation of many organic compounds mediated by hydroxyl radicals. In 1980, Cohen and Cederbaum [27] suggested that rat liver microsomes oxidized ethanol, methional, 2-keto-4-thiomethylbutyric acid, and dimethylsulfoxide via hydrogen atom abstraction by hydroxyl radicals. Then, Ingelman-Sundberg and Ekstrom [28] assumed that the hydroxylation of aniline by reconstituted microsomal cytochrome P-450 system is mediated by hydroxyl radicals formed in the superoxide-driven Fenton reaction. Similar conclusion has been made for the explanation of inhibitory effects of pyrazole and 4-methylpyrazole on the microsomal oxidation of ethanol and DMSO [29],... 

Until 1945 no anhydrides of xylitol or any other pentitol had been described. In that year a patent was granted to Grandel73 to make anhydrides of pentitols by heating them with a catalyst, followed by vacuum distillation. Xylitol on being heated with methionic acid followed by vacuum distillation gave monoanhydroxylitol and a dianhydro-(73) F. Grandel (to Alien Property Custodian), U. S. Pat. 2,375,915 (1945). 

Scheme 60). Griesbeck et al. assume that in a non-polar solvent such as benzene the intramolecular electron transfer from the methionic sulfur group is much faster than the abstraction of hydrogen from the hydroxyl group of the unprotected amino acid. C-Hydrogen abstraction leads to 313, whereas previous lactonization of the zwitterionic biradical 311 yields 314. Since the cis-hydroxy acid is not detected it is conceivable that it cyclizes immediately to the lactone 314. Photolysis of the corresponding methyl ester under the same conditions attains improved yields (84% combined) of two diastereomeric tricyclic products in a ratio of 48 52. 

Chemicals. The carbonyl compound standards 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, pentanal, hexanal, furfural, methional, phenylacetaldehyde, and (E)-2-nonenal were purchased from Sigma-Aldrich (Milwaukee, Wl). A stock solution containing a mixture of the standard compounds in ethanol was prepared daily in a concentration of 100 ppb each. An aqueous solution of the derivatization agent 0-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine (PFBOA) (Sigma-Aldrich, Milwaukee, WI) was prepared at a concentration of 6 g/L. PFBOA solution was prepared every 3 months and kept refrigerated. 

Optimization of Derivatization Procednre. Three parameters that may affect the partition of aldehydes between the headspace and the solution were tested derivatization time, temperature, and ionic strength. The effect of pH was not examined because it was previously shown that the natural pH of beer, 4.5, is sufficiently low for the derivatization reaction (6). Therefore, the pH of standard mixtures was adjusted to 4.5 using 0.1% phosphoric acid. Because methional appeared to be the most problematic aldehyde to detect, optimization was carried out in a 5% ethanol (pH 4.5) solution spiked with 5 ppb of methional. 

The effect of temperature on the extraction of methional from ethanol solution and its derivatization on a PFBOA-loaded fiber was examined for 35 and 50 °C (Figure 2). Increasing the extraction temperature caused an increase in the peak area of the derivatized methional. Based on this result, subsequent derivatizations were conducted at 50 °C. 

The optimal derivatization time was also tested. The ethanol solution spiked with 5 ppb of methional was exposed for 15, 30, 60, 90, and 120 min at 50 °C. it was determined that the time to reach equilibrium between stationary phase and sample head-space was 90 min (Figure 3). A derivatization time of 60 min at 50 °C appeared to be a good compromise between the time of reaction and analyte response. 

Figures. Derivatization time versus detector response of PFBOA derivative of methional.

Figure 4 shows that addition of salt (2 g of NaCl in 10 mb of methional solution) did not have any effect on the extraction and derivatization procedure (60 min, 50 °C). 

Description The ethanol solution spiked with 5 ppb of methional was... 

To refer to a figure or table Present-active Figure 1 shows as an example the mass spectrum of the PFBOA derivative of methional. (From Vesely et ah, 2003)... 

Methional reacts with PFBOA to form two oxime isomers. 

Methional was measured using the sum clthe two peak areas. 

The optimization solution contained 6% ElOH (pH 4. 5) spiked with 6 ppb methional (CHiSCHzCHjCHO. ... 

The SPME fiber was placed in the headspace of the PFBOA solution for 10 min (50 0. then the Pf BOA-loeded fiber was placed in the headspace of the methional solution (ID mL in a 20 ml vial). Temperaliire and lime were optimized. 

The derivatized methional wee detected in singfe-ion mode using GOMS (HPOS30 GC with DB-5 column end messr selective Agilent 5972A detector). 

The melhional recovery rale was determined using the method of standard addition a 5 ppb methional solution was spiked with 100 ppb... 

The aldehydes 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, methional, and phenylacetaldehyde are so-called Strecker aldehydes, formed as a result of a reaction between dicarbonyl products of the Amadori pathway and amino acids, having one less carbon atom than the amino acid (i). 

R - Pr, /-Pr) were obtained from the corresponding aldehydes (butyraldehydes, isobutyraldehyde) and ammonium sulfide, in the presence or in the absence of acetoin (29), while no such compounds were identified with methional and ammonium sulfide as the starting materials. Similarly, the higher aldehydes did not lead to the desired heterocycles, except for isovaleraldehyde (35),... 

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