Reductone-amino reaction

By Amadori Reaction. — 1-Amino-1-deoxy-D-fnictose derivatives (Amadori compounds) have been prepared by reaction of D-glucose vith a series of aliphatic amino acids (e.g. glycine, P-alanine, y-aminobutyric acid, 5-aminovaleric acid, e-aminocaproic acid and AT-formyl-L-lysine), and characterized by H- and C-n.m.r. and FAB-mass spectrometry and pH-potentiometric titration. The P-pyranose form dominates in aqueous solution. The basicity of the amino-group in these compounds is decreased (by -1.5 of the IKa value) relative to the parent amino acid. The formation of l-)V-butylamino-l-deoxy-4-0-(a-D-glucopyranosyl)-D-fructose by Amadori reaction of maltose and butylamine, and its conversion to the amino-reductone 23 have been reported. ... 

There are a number of chemical reactions which can participate in the formation of various types of amino-reductones including enaminols and enediamines. These amino-reductones are known to play important roles in the process-induced chemical changes in foods, especially in browning and in cooked flavor formation, and thus the over-all quality... 

These amino reductones described above are usually very unstable reaction intermediate compounds and, therefore, isolation and elucidation of their precise chemical structures by ordinary experimental techniques are rather difficult. However, owing to the recent remarkable progress in computational chemistry, various types of molecular orbital methods are now applicable to obtain needed information about their precise structures and chemical reactivities. For instance, the optimized structure of L-ascqrbic acid, an important acid-reductone in food and biological systems, was obtained by both semi-empirical and ab initio molecular orbital methods (Abe et aL, 1987, 1992). Semi-empirical molecular orbital calculations were also used to elucidate the autoxidation mechanism of L-ascorbic acid (Kurata et aL, 1996a,b). 

The most practical method for preventing WOF in meat products is to add antioxidants prepared from natural precursors such as sugars and amino adds by heating them to produce constituents that not only act as antioxidants but serve to enhance meaty flavor as well. The resulting Maillard products have been known to have antioxidant activity in lipid systems (6-8). It is assumed that the antioxidative property of the Maillard reaction is assodated with the formation of low molecular weight reductones and high molecular weight melanoidins (6, 7, 9-13). 

Omura, H. Inoue, Y. Eto, M. Tsen, Y.-K. Shinohara, K. Reaction products of triose reductone with some amino acids. Kyushu Daigaku Nogakubu Gakugei Zasshi 1974, 29, 61-70. 

Knowledge about the chemical structure of the antioxidative MRP is very limited. Only a few attempts have been made to characterize them. Evans, et al. (12) demonstrated that pure reductones produced by the reaction between hexoses and secondary amines were effective in inhibiting oxidation of vegetable oils. The importance of reductones formed from amino acids and reducing sugars is, however, still obscure. Eichner (6) suggested that reductone-like compounds, 1,2-enaminols, formed from Amadori rearrangement products could be responsible for the antioxidative effect of MRP. The mechanism was claimed to involve inactivation of lipid hydroperoxides. 

As shown above, glycine is formed again in the course of the Maillard reaction, during the conversion of the ARP into the reductones. Eventually it may react with these reductones or other electrophiles. Therefore the rate of the decrease of the concentration of the amino acid is not similar to the rate of the reaction with the sugar (Figure 1). The rate of consumption of monosaccharide, however, is a good measure of the reaction rate. 

This is a reaction of a-amino acids, in which they are oxidised to the corresponding aldehyde, giving off carbon dioxide, and ammonia is transferred to other components of the system, very little being liberated as such. The reaction is initiated by compounds, such as a-dicarbonyl compounds and their vinylogues, or compounds which can give rise to them readily, such as reductones by dehydrogenation or imino analogues by hydrolysis. The reaction may therefore be represented as follows ... 

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-... 

Its formation from rhamnose heated with piperidine acetate in ethanol, under the same conditions that produced amino-hexose-reductones from glucose and other hexoses, was described as early as 1963 by Hodge et al., who confirmed the structure by IR and NMR data and proposed a formation pathway. The formation from Amadori intermediates was been reviewed by Vernin (1981). Numerous model systems have confirmed that it is one of the main Maillard-reaction products. For instance we will mention the formation from L-rhamnose and ethylamine (Kato et al., 1972) and from pentose/glycine or alanine, whose mechanism was proposed by Blank and Fay (1996) and Blank et al. (1998), from the intermediate Amadori compound, /V-(l-deoxy-D-pentos-l-yl)glycine. Furaneol is also formed by recombination of... 

The chemistry of the browning reaction has been reviewed periodically (1-7). The carbohydrate-amino acid browning reaction produces literally hundreds of reaction products. Despite the fact that the Maillard reaction has been investigated for many years, we cannot as yet identify all the reactant compounds. The first steps are, however, clearly established. The aldose or ketose reacts with amine to produce N-substituted glycosyl amine (Fig. 1). This rearranges, as illustrated, to produce a 1-amino-desoxy-2-ketosyl amine. If it is blocked, the overall reaction is blocked. This key compound or compounds can then continue to react (Fig. 2). The desoxy-ketose or amadori rearrangement product can dehydrate to produce furfural-like compounds or, through the loss of water, produce reductones. All of these compounds can react with one another or with other amine compounds to produce a wide variety of reaction products. 

Fig. 8.27. Maillard reaction involved in the non-enzymic oxidative browning of plant tissues, (a) Formation of an imine by an amino acid reacting with an aldose (Ri = H) or ketose (Ri H). (b) Enolization of the imine to enaminol, then to an Amadori (Ri = H) or Heyns (Ri H) intermediate, (c) Breaking of the preceding intermediates, with the appearance of a reductone in redox equilibrium with an a-dicarbonylated compound, responsible for the non-enzymic oxidation phenomenon...

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