Reactions with Amino Compounds Maillard Reaction

4 Reactions with Amino Compounds Maillard Reaction) 

The consecutive reactions of N-glycosides partially correspond to those already outlined for acid/base catalyzed conversions of monosaccharides. However, starting with N-containing intermediates, which with the nitrogen function possess a catalyst within the molecule, these reactions proceed at a high rate under substantially milder conditions, which are present in many foods. 

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The chemical degradation of carbohydrates, particularly under acidic conditions, produces reductones, furan derivatives, pyruvaldehyde, and so on, which can condense, either among themselves or with amino compounds (Maillard reactions), to produce dark-colored, amorphous products, similar to humic substances. Pyruvaldehyde, which has been held to be an intermediate in Maillard reactions, has been identified in many soils. Such con-... 

The reaction of amino compounds with aldehydes or ketones associated with the formation of browning polymeric materials is known as Maillard condensation [2]. 

The results obtained with this procedure are similar to those previously reported in the literature by Hangartner, Hagenguth et al and Zeman et al (4, 2, 5, 6). The major exception, being the complete lack of alkylated pyrazines and alkylated thiophenes. These odour-intensive compounds arise from the thermal decomposition of proteins and sulphur containing amino acids. They also develop in the thermally induced reaction of proteins with carbohydrates (Maillard reaction). The authors indicated above have demonstrated that these compounds are invariably produced during the thermal treatment of sludge, a process which is not used in this Authority. 

Electron-spin resonance (e.s.r.) spectra with characteristic hyperfine structure have been recorded during the initial stages of the Maillard reaction between various sugar and amino compounds. The products responsible for the spectra appear to be IV, Af -disubstituted pyrazine radical cations. The pyrazine derivatives are assumed to be formed by the bimolecular condensation of two- and three-carbon enaminol compo-... 

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-... 

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. 

The reaction of dextrose with a nitrogen-containing compound, eg, amino acids or proteins, yields a series of intermediates which form pigments of varied molecular weight (Maillard reaction). The type of pigments produced is dependent on reaction conditions such as pH, temperature, and concentration of reactants. 

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. 

Amadori compounds (N-substituted-l-amino-l-deoxy-2-ketoses) are potential precursors to the formation of many of these heterocyclic volatile products. The secondary nitrogen in most Amadori compounds is weakly basic and is therefore a likely site for rapid nitrosation reactions via normal reactions with nitrous acid, under mildly acidic conditions. However, purified Amadori compounds are usually obtained only after tedious isolation procedures are invoked to separate them from the complex mixtures of typical Maillard browning systems. Takeoka et al. ( 5) reported high performance liquid chromatographic (HPLC) procedures to separate Amadori compounds in highly purified form on a wide variety of columns, both of hydrophilic and hydrophobic nature. They were able to thus demonstrate that reaction products could be followed for kinetic measurements as well as to ensure purity of isolated products. 

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