Lysine Maillard reactions with

Figure 9.8 Initial steps of the Maillard reaction with the formation of furosine (after hydrolysis with 7.8 M HCi) as well as of. Y-s-carboxymethyl lysine and erythronic acid (from Erbersdobler...

The Maillard reaction is likely to take on additional significance with the introduction of many new protein and peptide pharmaceuticals. For example, Tarelli et al. have demonstrated that lysine vasopressin undergoes rapid glycation in the presence of reducing sugars in both aqueous and solid formulations and that the N-terminal adduct can form rapidly even at — 20°C [52], A textbook that deals with the consequences for the chemical and life sciences of the Maillard reaction has been published [53]. 

A number of Maillard reaction products have been found to be mutagenic or carcinogenic (Lee and Shibamoto, 2002). Reactions of the lysine residue with other food components, including dehydroascorbic acid, result in crosslinking of the heated protein (Fayle et al., 2000). 

The extent of heat-induced changes in protein-rich foods can be measured by determining some early Maillard reaction products (O Brien and Morrissey, 1989). Acid treatment of protein-bound or free A -fructoselysine liberates lysine, with a yield of 50%, and two other amino acids, furosine (20%) and pyridosine (10%) (Figure 13.1). The three products that result from hydrolysis of A -lactuloselysine are formed in the proportions of approximately 5 3 to 4 1 to 2, however the yield of different derivatives is variable. Therefore, in order to use these unique amino acids as indicators of changes in lysine content, the hydrolysis should be carried out in strictly-defined conditions. Furosine is present in various food products in a very wide range of concentrations (Table 13.2). 

Change of pH of Blood Plasma A slightly acid medium is usually needed for the Maillard reaction, but in some cases, e.g., with lysine-rich proteins, a slightly alkaline pH is also operating. Thus a small change in pH, due to the nature of food consumed or the pathologic metabolism of foodstuffs, can affect Maillard reactions in vivo. 

A. Amoldi and G. Boschin, Flavors from the reaction of lysine and cysteine with glucose in the presence of lipids, in Thermally Generated Flavors Maillard, Microwave, and Extrusion Processes, T. H. Parliment, M. J. Morello, and R. J. McGorrin (eds), American Chemical Society, Washington, DC, 1994, 240-250. 

Nutritional Effects Due to the Blockage of Lysine. The most important Maillard reaction in food proteins occurs with the c-amino group of lysine. Since lysine is an essential amino acid, nutritional consequences can be expected. These depend on the chemical structure of the lysine derivatives formed. 

Casein-Bound 3H Lysine in Untreated, Early, and Advanced Maillard Casein (41). Goat sodium caseinate biologically labelled with L-4,5-3H-lysine was treated with glucose under conditions inducing early and advanced Maillard reactions. The two preparations contained about the same reactive lysine (see Table III) the early Maillard 3H-casein contained only c-deoxyfructosyllysine as Maillard products and the advanced Maillard 3H-casein contained some c-deoxy-fructosyllysine and unidentified derivatives of lysine and glucose as brown pigments. 

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