Coloured Polymeric Maillard Products

According to Rizzi,182 the types of systems studied are conveniently divided into simple model systems of reducing sugars and amines or amino acids, sugars and proteins, and sugars by themselves (i.e., caramelisation). Each of these will now be considered in turn, bearing in mind, in particular, the key question of whether the backbone of the polymeric material itself is coloured or whether the colour resides in moieties attached to an essentially colourless backbone. 

1 Model Systems of Reducing Sugar and Amines or Amino Acids 

Electron-spin resonance (ESR) indicated free radicals in a brown polymer (mean ca 1 kDa by field-desorption MS) from a glucose-4-chloroaniline model system.185 Such free radicals (see Chapter 2) could be a source of visible colour. Exposure of the melanoidin to nitric oxide, a radical-trapping agent, diminished the ESR signal by 48% and changed the colour to red-brown. 

Blue-Mi is the name given to a pigment isolated from D-xylose-glycine.75 It was identified as the pyrrolopyrrolium compound 30 and assumed to be a dimer of the yellow pyrrolopyrrole-2-carboxaldehyde.186 It is capable of polymerising further to melanoidins and, similar to melanoidins, it has strong antioxidant activity. There is evidence of another pigment, Blue-M2, with molecular mass (MM) = 0.942 kDa. 

Melanoidins based on polymeric pyrroles were dealt in Chapter 2. 

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