Amines Maillard reactions

Because of their significant electrophilic character, aldehydes are often unstable and will react with nucleophiles. For example, a common reaction of aldehydes is the formation of a hemiaminal with amines. If the amine is a primary amine, the hemiaminal can dehydrate to form an imine as shown in Figure 21. The reaction of aldehydes with primary and secondary amines is a well-studied reaction pathway because it is a common reaction pathway of reducing sugars and amino acids, and this reaction pathway is known as the Maillard reaction (40). In the case of amino acids and sugars, this reaction leads to discoloration, or browning. This reaction will be discussed in greater detail in the Amines-Maillard Reaction section. 

Dextrose may cause browning of tablets containing amines (Maillard reaction). 

Fig. 12.—Carbonyl-amine reactions leading to Maillard reaction products and reductones (adapted from Ref. 51a).

The formation of oxygen-containing heterocyclic compounds is also a consequence of the Maillard reaction. Amines and amino acids have a catalytic effect upon the formation of 2-furaldehyde (5), 5-(hydroxy-methyl)-2-furaldehyde (11),2-(2-hydroxyacetyl)furan (44),2 and 4-hy-droxy-5-methyl-3(2//)-furanone (111) (see Ref. 214). This catalytic effect can be observed with several other non-nitrogenous products, including maltol. The amino acid or amine catalysis has been attributed to the transient formation of enamines or immonium ions, or the 1,2-2,3 eno-lization of carbohydrates. Of interest is the detection of A -(2-furoyl-... 

Several other non-nitrogenous products have been identified as products of the Maillard reaction. These include butanol, butanone, butane-dione, and pentane-2,3-dione as well as dihydroxyacetone, glycer-aldehyde, and D-erythrose. Obviously, the same products are present after mild acidic or basic degradation of carbohydrates. Thus, the necessity of an amine or amino acid in the mechanism of their formation is uncertain. 

The products in these two groups are capable of further reaction, and the subsequent stages of the Maillard reaction involve the interaction of furfurals, fu-ranones and dicarbonyls with other reactive compounds such as amines, amino acids, hydrogen sulphide, thiols, ammonia, acetaldehyde and other aldehydes. 

Wirth DD, Baertschi SW, Johnson RA, et al. Maillard reaction of lactose and fluoxetine hydrochloride, a secondary amine. J Pharm Sci 1998 87(1) 31 39. 

Dicarbonyls, which are among the products of the Maillard reaction, can react with amines in the Strecker reaction, producing a variety of flavourful... 

Formation of novel free radical products at an early stage of the Maillard reaction was demonstrated by use of ESR spectrometry. Analyses of the hyperfine structures for various sugar-amino compound systems led to the conclusion that the radical products are N,N -disubstituted pyrazine cation radicals. These new pyrazine derivatives are assumed to be formed by bimolecular condensation of a two-carbon enaminol compound involving the amino reactant residue. The presence of such a two-carbon product in an early stage reaction mixture of sugar with amine was demonstrated by isolation and identification of glyoxal dialkylimine by use of TLC, GLC, NMR, MS and IR. 

Several mechanisms have been reported for pyrazine formation by Maillard reactions (21,52,53). The carbon skeletons of pyrazines come from a-dicarbonyl (Strecker) compounds which can react with ammonia to produce ot-amino ketones as described by Flament, et al. (54) which condense by dehydration and oxidize to pyrazines (Figure 6), or the dicarbonyl compounds can initiate Strecker degradation of amino acids to form ot-amino ketones which are hydrolyzed to carbonyl amines, condensed and are oxidized to substituted... 

Food as Source of Starting Materials for Maillard Reaction in Vivo Nutrients are, of course, the origin of many different reducing sugars and amines or proteins, which are suspected to undergo a Maillard reaction in vivo. 

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