Melanoidins precursors

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). 

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). 

Examining a defatted extract of roasted coffee showed that it could similarly be separated into three fractions on Sephadex G25-fine. When the middle fraction was collected, freeze-dried, roasted at 200 °C for 3 min, and re-analysed, most of it had been converted into the fast-running high-MM peak, thus demonstrating that low-molecular-mass (LMM) melanoidins act as precursors to high-molecular-mass (HMM) ones.83... 

Young D. K., Sprang S. R., and Yen T. E. (1977) Preliminary investigation on the precursors of the organic components in sediments-melanoidin formations. In Chemistry of Marine Sediments (ed. T. E. Yen). Ann Arbor Science,... 

There have been a number of reports on the Maillard reaction. Oxidation of the melanoidins produced from D-glucose and glycine with potassium permanganate and peracetic acid yielded, among other products, furan-2,5-dicarboxylic acid, suggesting that 5-hydroxymethyl-2-furaldehyde is a precursor of the melanoidic pigments produced in the Maillard reaction. 2-(2-Formyl-5-hydroxymethyl-... 

To identify the natural precursors of this type of radical, several binary mixtures of mono-, di- and polysaccharides, amino acids and proteins have been thermally treated, brown colored melanoidins have been isolated by ultracentifiigation and then analyzed by EPR spectroscopy for paramagnetic behavior (Hofmann, unpublished results). In a heated mixture of bovine serum albumin (BSA), which was chosen as a model food protein, and glucose, an intense radical with a g-value of 2.0038 was detected in the melanoidins (15). The EPR signal of that radical, displayed in Figure 3, was identical widi diat detected in the coffee melanoidins (cf. Figure 2). 

The possibility of the formation of nitrosamines and their concentrations in foods depend on many factors, such as the presence and quantity of amines and their precursors, type and quantity of nitrosation agents, pH, temperature, reaction time, composition of food (such as fat content), method of heat treatment, presence of substances that catalyse nitrosation reaction (e.g. rhodanides and to a lesser extent chlorides), and the presence of inhibitors (e.g. ascorbic acid, its esters and salts, sulfur dioxide, phenolic antioxidants, such as gallates and melanoidins). 

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