Maillard condensation

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... 

L.-C. Maillard, Condensation des acides amines en presence de la glycerine Cycloglycylglycine et polypeptides, C.R. Hebd. Seances Acad. Sci., 1911, 153, 1078-1080. 

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

In lakes, the pool of dissolved organic carbon (DOC) is dominated by dissolved humic substances (up to 80% of the DOC). Lake humic substances are similar to soil humic substances in that carboxyl, hydroxyl, phenol, and probably methoxyl groups are of major significance. Fluorescence spectra of DOC may be interpreted in terms of the different geochemical origins of DOC (e.g., allochthonous versus algal derived). One or more moieties of dissolved humic substances are produced autochthonously mechanisms may include polymerization of phenols (promoted by transition metals), Maillard condensations, or oxidation via phenolase systems. Aliphatic structural units in dissolved humic substances provide a flexible conformation to the humic substance molecule. ... 

Chemical activity can occur whenever reactions are possible. Usually, with solid and dry forms these reactions do not happen or take place only slowly. Here too low temperatures decrease the risk. Natural food samples such as freeze-dried milk or fruit juice can be subject to Maillard condensations. 

On the other hand, furosine has the big advantage that it is a direct marker for a real existing reaction product of lysine, which has nutritional relevance. It represents the main reaction product of the initial stage of Maillard condensation and in this way a sector of heat damage, which is most interesting for heated milk and milk products. 

In dairy products also hydroxymethylfurfural (HMF) and lactulose are common markers. For the determination of HMF, which also results from the Maillard condensation (18), precursors of browning products in milk are transformed to HMF after addition of oxalic acid and following heating (79). Principally, the HMF value of a milk can be used as an indicator for the heating process, but data from literature offer a wide range for this value which suspect that the HMF determination is insufficiently reproducible between laboratories. In particular, the level of HMF in untreated material, measured during the determination of "total HMF" and subtracted from the levels in treated milks, is a source of variation (20). However a comparison between the furosine and the HMF-method demonstrated the usefulness of the HMF-method as a rapid and simple measure of heat damage caused by the UHT process (77). 

Since the pioneering synthesis of this type of glycoconjugate first described by Maillard el al. in the late 1980s via condensation of 2-formylphenyl tetra-O-acetvl-/)-D-glucopyranoside with pyrrole,132 improved synthetic methodologies have generated... 

Milk solids are normally used as either milk powder or sweetened condensed milk in food manufacturing. Skim milk solids are an essential part of toffees as well as contributing useful colour and Maillard reaction flavours to baked goods. 

One of the bars to the use of lactose as a food ingredient is its limited solubility. This can be overcome by enzymatically splitting the lactose to its component monosaccharides dextrose and galactose. These monosaccharides are much more soluble than lactose but can still undergo the Maillard reaction. If the lactose is split into its constituent monosaccharides, whey can be condensed to a relatively stable high solids syrup. These syrups tend to carry some cheese flavour notes but, where used appropriately, can contribute beneficial colours and flavours in biscuits. 

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...

Maillard products are not only formed during cooking and other heat processing of foods, but also accumulate in some products that are rich in proteins and reducing sugars, e.g. condensed milk during months of storage at... 

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-... 

In summary, there are at least four ways in which residual moisture in the amorphous state can impact on chemical reactivity. First, as a direct interaction with the drug, for example, in various hydrolytic reactions. Second, water can influence reactivity as a by-product of the reaction, by inhibiting the rate of the forward reaction, for example, in various condensation reactions, such as the Maillard reaction. Third, water acting locally as a solvent or medium facilitating a reaction, without direct participation. Finally, by virtue of its high free volume and low Tg, water can act as a plasticiser, reducing viscosity and enhancing diffusivity [28]. 

Another major problem associated with the extraction of DNA from archaeological specimens is that the procedure often co-extracts impurities that can later complicate, or prevent, the study of the extracted DNA by inhibiting PCR amplification (reviewed by 5). Commonly encountered inhibitory substances found in aDNA extracted from teeth, bones, mummified tissue, and coprolites include humic acids, ftilvic acids, tannins, porphyrin products, phenolic compounds, hematin, and collagen type I (37—42). The formation of Maillard products, commonly encountered in coprolite samples, can also prevent PCR amplification by causing DNA to become inaccessibly trapped in these sugar-derived condensation products (12). As the negative results in many aDNA studies are attributed to the presence of PCR inhibitors, our extraction method outlined below pays particular attention to the problem and offers a simple test for the presence of PCR inhibitors in DNA extracts. 

Ten years ago Kawamura (1 ) published a brief historical review on this reaction in memory of the sixtieth anniversay of its first report by Louis-Camille Maillard (2. The first Maillard paper was presented on January 8, 1912, by Armand Emile Justin Gautier (1837-1920) in a session of the Academy of Sciences in Paris. Six weeks earlier (November 27, 1911) a remarkable study was reported by Maillard (3) on the condensation of amino acids by use of glycerol. The method of peptide synthesis by Emil Hermann Fischer (1835-1919) was known to him. However, Maillard searched for milder conditions. 

Ame Pictet (1857-1937) of the University of Geneva reported the formation of pyridine and isoquinoline bases from acid hydrolyzate of casein in the presence of formaldehyde in 1916 (8). Maillard ( ) claimed priority over him in discovering the condensation of amino acids with aldehydes or sugars to yield pyridine bases by citing his own paper (10). 

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