Arginine glyoxal compounds

Table 4.16. Concentrations of pentosidine in foods guanidino group of arginine. The recently identified compound Bisarg (Formula 4.100) is a condensation product of 2 molecules each of arginine, glyoxal and furfural. Apart from the protein cross-linking properties, the intensive brown-orange color of Bisarg should be mentioned.

Figure 12.10 The imidazole reaction between glyoxal and arginine creates cyclic addition compounds lacking positive charge.

The reaction of dicarbonyl compounds, such as glyoxal or phenylglyoxal, with a guanidinyl group, such as that of an arginine residue, proceeds to yield a more stable linkage due to the formation of a cyclic derivative (Reaction 46). 

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). 

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