Maillard browning melanoidins

The final polymerization products (melanoidins) are brown and hence dairy products which have undergone Maillard browning are discoloured and aesthetically unacceptable. 

Figure 1. Sugar-amine Maillard browning reactions Two pathways to melanoidins and byproducts. (Reprinted with permission from ref. 12. Copyright 1967 Avi Publishing.)...

Lipid oxidation products react with proteins and other amino compounds to form brown substances, similar to melanoidins. The formation of such brown substances was reviewed already at the first Maillard Symposium.150 The pigments formed are partly soluble in chloroform-methanol and partly insoluble, whereas true melanoidins are largely water-soluble. As most brown pigments of fish muscle are soluble in benzene-methanol and only to a lesser extent in water, the implication is that here oxidised lipid-protein interactions are more important than Maillard browning due to ribose-amino acid interactions. 

Casein heated in aqueous solution with furfural rapidly turns orange-brown. Melanoidins (> 10 kDa), isolated by ultracentrifugation, were enzymically hydrolysed and the product was separated by HPLC. Two peaks led to red compounds in the ratio 1 7, which were unequivocally identified by Hofmann191 as the lysine analogues of 24a and 24b (MM = 0.476 kDa), respectively. This is the first demonstration of the attachment of a specific type of coloured Maillard product to a protein... 

Because caramels are mainly prepared as coloring matter, a dark-brown melanoidin is a most essential and desirable result of the process. Reactions which lead to melanoidin are called the Maillard reaction. There is some controversy about the formal meaning of this reaction. Ellis considered... 

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... 

The last report of Maillard (21) is rather a review in nature, with more than 50 references. The chemical natures not only of humus in soil but also of mineral fuel (coal) and browning in food material were discussed, especially in relation to the presence of nitrogen in browned products, which was inferred to be derived from amino acids (and related nitrogenous materials) used for synthetic "melanoidins". 

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. 

C. M. Brands and M. A. J. S. van Boekel, Kinetic modelling of Maillard reaction browning effect of heating temperature, in Melanoidins in Food and Health, Vol. 2, J. M. Ames (ed), European Communities, Luxembourg, 2001, 143-144. 

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. 

Melanoidins. Brown pigments produced in Maillard reactions. 

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