Strecker aldehyde formation

Strecker Aldehyde Formation. Formaldehyde, acetaldehyde and iso-butyraldehyde were formed by Strecker degradation of glycine, alanine and valine, respectively. Relative concentrations of aldehydes produced by microwave and conventional heating to comparable temperature is shown in Table I. Significantly higher concentrations were observed for microwave heated samples. 

Furthermore, the results revealed that, in addition to MBT level, 3-(methylthio)propanal and phenylacetaldehyde levels were significantly increased in the illuminated sample (Table 1). The formation of such Strecker aldehydes induced by light has also been observed earlier in model systems containing catechin, riboflavin, and the respective precursor amino acids [16] and has been reported for light-treated skim milk [17]. However, the mechanism of Strecker aldehyde formation induced by light is still unclear. 

Strecker aldehyde are generated by rearrangement, decarboxylation and hydrolysis. Thus the Strecker degradation is the oxidative de-amination and de-carboxylation of an a-amino acid in the presence of a dicarbonyl compound. An aldehyde with one fewer carbon atoms than the original amino acid is produced. The other class of product is an a-aminoketone. These are important as they are intermediates in the formation of heterocyclic compounds such as pyrazines, oxazoles and thiazoles, which are important in flavours. 

Martin, F. L., Ames, J. M. (2001). Formation of Strecker aldehydes and pyrazines in a fried potato model system. 

Many desirable meat flavor volatiles are synthesized by heating water-soluble precursors such as amino acids and carbohydrates. These latter constituents interact to form intermediates which are converted to meat flavor compounds by oxidation, decarboxylation, condensation and cyclization. 0-, N-, and S-heterocyclics including furans, furanones, pyrazines, thiophenes, thiazoles, thiazolines and cyclic polysulfides contribute significantly to the overall desirable aroma impression of meat. The Maillard reaction, including formation of Strecker aldehydes, hydrogen sulfide and ammonia, is important in the mechanism of formation of these compounds. 

Oxidation of carbohydrate or Strecker aldehyde by S-MnOz to form carboxylic acid, or formation of carboxylic acid during Strecker degradation... 

The question of the fate of the "Strecker" aldehydes requires an answer. By converting the amino acid phenylalanine to yield aroma compounds, phenyl acetaldehyde is liberated. Because of its phenyl ring it is a good detector compound. We were able to establish some of its reaction products. For example, we have identified, among others, phenylethylpyrazine, phenylfuran, phenylethylpyrrole and phenylpyri-dine. We assume that aldol condensations are responsible for the formation of these compounds. Figure 5 illustrates our assumption.We have identified several compounds the structures of which make probable an aldol condensation (3-(2 -furyl)-2-phenyl-2-propenal, phenyl hydroxyketones) likely. This assumption is supported by the identification of pyrazines with up to 5 carbon atom side chains in other experiments. 

Chemical oxidation reactions and Strecker degradation of amino acids may also result in aldehyde formation (16). These reactions are important for the formation of acetaldehyde in baked or heated Sherries. Chemical oxidation reactions catalyzed by metal ions (Cu, Fe, Mn, Mo) can result in aldehyde production in oak aged distillates (20). Such reactions may also result in the formation of oxidation products from fatty acids released during the secondary fermentation of sparkling wines (21). 

Various Isopentyl-substituted pyrazines, such as 2-lsopentyl-3-methylpyrazine, 2-isopentyl-5-methylpyrazine, 2-isopentyl-6— methylpyrazlne, 2-i8opentyl-5,6-disiethylpyrazlne, 2-isopentyl-3,5-dimethylpyrazlne and 2-isopentyl-3,6-dimethylpyrazlne were identified from the thermal reaction of glucose and leucine (12). The formation mechanisms for these compounds may also involve the reaction of 3,6-dihydropyrazine with isovaleraldehyde, the Strecker aldehyde of leucine. Kltamura and Shibamoto (13) described 2-lsopen-tyl-5,6-dimethylpyrazlne as having a caramel-like, coffee and sweet aroma. Although isopentyl-substituted pyrazines have not yet been reported in cocoa, they could, if present, be very Important contributors to that characteristic aroma. 

Strecker [34] discovered that the reaction between amino acids (glycine, alanine, leucine) and the tricarbonyl compound alloxan yields CO2 and aldehydes. The Strecker degradation of amino acids occurs also with dicarbonyl compounds [35] including those that are formed in the course of the Maillard reaction, in particular deoxyglycosones and some of the smaller sugar fragments like 7 and diacetyl. Fig. 3.22 shows the reaction pathway that involves the formation of an imine 8, followed by decarboxylation and liberation of the resulting aminoketo compound and the Strecker aldehyde from the intermediate 10. Odour-active Strecker aldehydes which... 

In the presence of oxygen, intermediate 10 can undergo oxidation and give rise to the formation of the aminoketo compound 11 and subsequently an acid, the so-called Strecker acid [36], The formation of Strecker acid, however, is not possible if dicarbonyls such as 4 are present in form of their stable cyclic hemiacetals, as shown by Hofmann and co-workers [36]. The same group revealed also that Strecker aldehydes can be formed via an oxidative degradation of Amadori compounds, as shown for the Amadori compound of phenylalanine and glucose [37],... 

Hofmann T, Schieberle, P. Formation of aroma-active Strecker aldehydes by a direct oxidative... 

According to Carlin et al. (1986), the exact mechanism of oxazole formation is not known, despite the previous schemes proposed by Vitzthum and Werkhoff (1974a,b) and by Ohloff and Flament (1978). Formation pathways were proposed by Baltes and Bochmann (1987d) and Mottram (1991). For Vitzthum and Werkhoff (1974b), one pathway could be the decarboxylation of serine or threonine into ethanolamine or methylethanolamine condensation with an aldehydic compound into an oxazolidine, then oxidation into an oxazole unsubstituted or methylated on position 5 and bearing an alkyl or an acyl radical on position 2. Another pathway could be the condensation of amino acids with a-dicarbonyl compounds, followed by a Strecker degradation, formation of an a-amino ketone which, after acylation... 

In the sample based on MIL and methylglyoxal, the ratio of Strccker aldehyde to sotolone was about 1 2 at pH 5 (Table VT). Consequently, the Slrecker degradation of HIL is a competitive reaction to the formation of sotolone. In contrast. only traces of Strecker aldehyde were detected In the sample containing the laciom-ADF, i.e about 50 times less than in the reaction with HIL 1 he formation orsololoiir from ADF is the favoured reaction, most likely due to the blocked carboxyl pmnp... 

Copper-promoted autoxidation of D-finctose-amino acids may be accompanied by the Strecker-like degradation pathway, which starts with decarboxylation of tire D-araZ)mo-hexos-2-ulose-amino acid adduct 64 and results in formation of the respective Strecker aldehydes. ... 

D. R. Cremer, M. Vollenbroeker, and K. Eichner, Investigation of the formation of Strecker aldehydes from the reaction of Amadori rearrangement products with a-amino acids in low moisture model systems, Eur. Food Res. Technol, 211 (2000) 400-403. 

T. Hofmann and P. Schieberle, Formation of aroma-active Strecker-aldehydes by a direct oxidative degradation of Amadori compounds, J. Agric. Food Ghent., 48 (2000) 4301-4305. 

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 very low activation energy for 2-acetyl-l-pyrroline may help explain why this volatile is found by sniffing methods in nearly every food stndied. It appears that this compound is very readily formed even nnder mild heating conditions. This fact, coupled with its extremely low sensory threshold, make its detection in foods likely. The Strecker aldehydes, isovaleraldehyde and phenylacetaldehyde, followed similar kinetics during heating. This is due to the similar mechanism of formation and the fact that they are both consumed through reaction to form 5-methyl-2-phenyl-2-hexenal [39]. 

The reactions between a-dicarbonyl compounds, like the deoxyosones obtained in the Maillard reaction, and amino acids are classed under the term Strecker reaction. This reaction leads to the formation of aldehydes (Strecker aldehydes), CO2 and a-aminoketones on oxidative decarboxylation of the a-amino acids (Formula 4.88). It occurs in foods at higher concentrations of free amino acids and under more drastic reaction conditions, e. g., at higher temperatures or under pressure. 

Table 21.25. Formation of free amino acids, accompanying Strecker aldehydes and amines in cocoa...

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