Maillard reaction melanoidins

Monosaccharides are probably involved in the browning reactions that occur during the roasting of coffee. Caramelization involving the sugars alone, and Maillard reactions, between sugars and free amino acids, produce polymeric yellow to dark brown substances, known as melanoidins. These melanoidins can be extracted into hot water, separated and characterized.105... 

An effort has also been made to determine the structure of products providing coloration in the Maillard reaction prior to melanoidin formation. The reaction between D-xylose and isopropylamine in dilute acetic acid produced 2-(2-furfurylidene)-4-hydroxy-5-methyl-3(2/f)-furanone (116). This highly chromophoric product can be produced by the combination of 2-furaldehyde and 4-hydroxy-5-methyl-3(2//)-furanone (111) in an aqueous solution containing isopropylammonium acetate. The reaction between o-xylose and glycine at pH 6, under reflux conditions, also pro-duces " 116. Other chromophoric analogs may be present, including 117,... 

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). 

With the single exception of the stable free radical observed in melanoidin prepared from the glycine-glucose reaction ( 7 ) > there have been no reports of free radical formation in the early stages of the Maillard reaction. We have observed the... 

A number of studies have detected Maillard reaction products (melanoidins) in refractory organic matter from natural environments—for example, from sediments from a west African upwelling (Zegouagh et al., 1999) and archeological plant remains (Evershed et al., 1997). Poirer et al. (2000,2002) and Quenea et al. (2006a) showed that the refractory organic matter isolated from different soils consists in part of cross-linked melanoidins poorly resolved by 13C NMR spectroscopy. The presence of amide structures in soil as elucidated by 15N NMR is ascribed to either preserved proteinacious structures or melanoidin-type macromolecules (Derenne and Largeau, 2001). 

The brown product or melanoidin which results from the Maillard reaction has been isolated from the products from various mixtures of reactants by numerous workers. A selection of these is given below. Maillard72, studied the interaction of D-glucose and other reducing sugars with glycine and several other amino acids at 34°, 40°, 100°, and 150°. 

It is worth noting that Mauron7 calls the three stages Early, Advanced, and Final Maillard reactions, respectively. The way these reactions fit together is outlined in Scheme 1.1. The final products of nonenzymic browning are called melanoidins to distinguish them from the melanins produced by enzymic browning. Theoretically, the distinction is clear however, in practice, it is very difficult to classify the dark-brown products formed in foods, since they tend to be very complex mixtures and are chemically relatively intractable. 

Scheme 2.3 Maillard reactions the two major pathways from Amadori compounds to melanoidins (based on Hodge213)...

Much attention has recently been paid to arginine as a melanoidin precursor. In a model system, lV -acetylarginine was first allowed to react with glyoxal in aqueous solution at pH 7, followed by furfural. Repeated chromatography of the aqueous residue after ethyl acetate extraction led to a 1% yield of the deep red 29.180 Such a compound provides an example of a potentially coloured crosslink in proteins derived by the Maillard reaction (see Chapter 8). 

Clearly, Class III and IV caramels are close to melanoidins produced by the Maillard reaction, but detailed structures for the coloured components cannot be given for any of these commercial caramels. 

The Maillard reaction can affect the activity of enzymes in at least two ways, through glycation or through interaction with melanoidins. 

Overall, there is no doubt that the Maillard reaction produces substances with an antioxidative effect, but it is by no means clear as yet how and to what extent that effect is exerted. Melanoidins not only have increased reducing power, but are able to complex metals and, in this way, lower their ability to act as catalysts in lipid and other oxidations. 

A. Amoldi and G. Boschin, Low molecular weight coloured compounds from Maillard reaction model systems, in Melanoidins in Food and Health, Vol. 2, J. M. Ames (ed), European Communities, Luxembourg, 2001, 23-29. 

T. Hofmann, 4-Alkylidene-2-imino-5-[4-alkylidene-5-oxo-l,3-imidazol-2-inyl]aza-methylidine-l,3-imidazolidine —A novel colored substructure in melanoidins formed by Maillard reactions of bound arginine with glyoxal and furan-2-carboxaldehyde, J. Agric. Food Chem., 1998, 46, 3896-3901. 

U. Lessig and W. Baltes, Model experiments on the Maillard reaction. VI. Structural studies on selected melanoidins, Z. Lebensm. Unters. Forsch., 1981, 173, 435 144 via Food Sci. Technol. Abstr., 1982, 14, 6A528. 

T. Hofmann, Studies on melanoidin-type colourants generated from the Maillard reaction of casein and furan-2-carboxaldehyde — chemical characterisation of a red coloured domaine, Z. Lebensm. Unters. Forsch, 1998, 206, 251-258. 

F. Hayase, Scavenging of active oxygen by melanoidins, in The Maillard Reaction Consequences for the Chemical and Life Sciences, R. Ikan (ed), Wiley, Chichester, 1996, 89-104. 

Caramel in this context means a brown colour that is produced either traditionally by heating sugar or as a very intense product that is made by heating carbohydrate, usually glucose syrup, with ammonia. Caramel colour is the product of the Maillard reaction, i.e. the reaction of a reducing sugar with an amino group. Chemically the colour is a melanoidin - these substances are extremely stable and can be used in any type of confectionery. 

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