Maillard reaction Amadori rearrangement

Degradation Rearrangement Hydrolysis Double bond shift Ring transformation Ring-contraction Ring-expansion Ferrier carbocyclization Anomerization Aromatization Maillard reaction Amadori reaction... 

Fig. 6.25. Simplified mechanism of two degradation reactions between peptides and reducing sugars occurring in solids, a) Maillard reaction between a side-chain amino (or amido) group showing the formation of an imine (Reaction a), followed by tautomerization to an enol (Reaction b) and ultimately to a ketone (Reaction c). Reaction c is known as the Amadori rearrangement (modified from [8]). b) Postulated mechanism of the reaction between a reducing sugar and a C-terminal serine. The postulated nucleophilic addition yields an hemiacetal (Reaction a) and is followed by cyclization (intramolecular condensation Reaction b). Two subsequent hydrolytic steps (Reactions c and d) yield a serine-sugar conjugate and the des-Ser-peptide...

The Maillard condensation is one of the most extensively studied reactions within the field of degradation chemistry, particularly in the area of food and nutritional science. Louis Mallard reported in 1912 that some amines react with reducing carbohydrates to produce brown pigments. The condensation typically yields a simple glycosylamine, which then readily undergoes the Amadori rearrangement to produce 1 -amino-1 -deoxy-2-ketoses [95]. Reducing carbohydrates... 

Thus we propose the existence of a new pathway to browning in the Maillard reaction, involving sugar fragmentation and free radical formation prior to the Amadori rearrangement. 

The mechanism proposed by Hodge in 1953 U) for the early stages of the Maillard reaction, involving the Amadori rearrangement as a key step, has been accepted over a quarter of a century as a most apt description. Here, we propose a new mechanism... 

It is well known that the Maillard reaction in foods is initiated by the formation of colorless and tasteless intermediates, which preferentially are formed in low-moisture systems ( ,5.). In this way by reaction of glucose with amino acids fructose-amino acids are formed via Amadori rearrangement of the primary glucosyl-ami-no acids (1 ). Fructose-amino acids e.g. have been isolated from freeze-dried apricots and peaches ( 6,7,8j. Amadori compounds arising from aldoses and amino acids are formed during drying of foods of plant origin and can be easily detected by amino acid analysis (j>). 

Figure 43 Initial steps of the Maillard browning reaction involving an Amadori rearrangement stable intermediate.

Figure 44 Maillard reaction of lactose and fluoxetine HCI yielding major degradants glycosylamine, Amadori rearrangement product, and N-formyl fluoxetine.

Results of the many investigations into the mechanism of the Maillard reaction support one of two main theories. The first assumes the formation of glycosylamines which undergo the Amadori (or, for ketoses, the Heyns) rearrangement. The 1-amino-1-deoxyketose derivative (or 2-amino-2-de-... 

This article describes a study on the catalytic role of phosphate in the Maillard reaction focussing on the first steps of the cascade of reactions, i.e. the conversion of the starting materials, monosaccharide and glycine, into the so-called Amadori Rearrangement Product (ARP). 

It may be concluded that the mechanism of the "early phase" of the Maillard reaction is not dramatically changed by the addition of phosphate. It is therefore clear that the phosphate did not act as a nucleophile in the reaction, giving a reactive intermediate, in the rate-limiting step of a typical phosphate-dependent mechanism, but acts as a basic catalyst during the Amadori rearrangement. 

Aldoses undergo the Amadori rearrangement and subsequently turn into caramels, the natural brown food colorants, and/or heteroaromatic compounds — derivatives of pyrrole, imidazole, and pyrazine. Ketoses react similarly into ketosylamino acids or ketosylamines, which, in the first step, undergo the Heyns rearrangement (5.17-5.23). These rearrangements are the first steps of either thermal or enzymatic (the Maillard reaction) reactions resulting in the browning of food and the aroma of roasted, baked, or fried foodstuffs. 

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