Maillard lysine

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]. 

The generation of artifacts has also been an intermittent concern. Hayashi et al.59 reported a heat-induced artifact for conversion of Amadori products of the Maillard reaction to V -(carboxymcthyl) lysine that had the potential to affect IHC staining. However, among thousands of articles pertaining to... 

Miki Hayashi C, Nagai R, Miyazaki K, et al. Conversion of Amadori products of the Maillard reaction to N(epsilon)-(carboxymethyl)lysine by short-term heating possible detection of artifacts by immunohistochemistry. Lab. Invest. 2002 82 795-808. 

Amino Acid Content. Amino acid content of field pea products is related to protein level, method of processing, and fraction (starch or protein). The protein fraction contains fewer acidic (glu, asp) amino acids than the starch fraction and more basic (lys, his, arg) amino acids than the starch fraction. Also, there are more aromatic (tyr, phe) amino acids, leu, iso, ser, val, and pro in the protein fraction than in the starch fraction (5). An amino acid profile of pea protein concentrate shows relatively high lysine content (7.77 g aa/16 g N) but low sulfur amino acids (methionine and cystine) (1.08-2.4 g aa/16 g N). Therefore, it is recommended that air classification or ultrafiltration be used because acid precipitation results in a whey fraction which contains high levels of sulfur amino acids (12,23). Also, drum drying sodium proteinates decreases lysine content due to the Maillard reaction (33). 

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). 

The factors affecting the Maillard reaction include temperature, time, moisture content, concentration, pH, and nature of the reactants. - It has been shown that, out of 21 amino acids, glycine, lysine, tryptophan, and tyrosine provide the most intense browning when exposed to five saccharides, especially a-lactose. The Maillard reaction is also responsible for the decreased availability of lysine in proteinaceous foods. 

Several markers for the Maillard reaction have been described in the literature. For example, the product initially formed between glucose and lysine is partly transformed into furosine (Heyns et ah, 1968) on acid hydrolysis. Conversely, the fluorescent amino acid pentosidine (Sell and Monnier, 1989) is an advanced glycation endproduct (AGE) and may form covalent bonds between proteins (cross-linking). Furthermore, the Maillard reaction leads to an increase in characteristic fluorescence (excitation 370 nm, emission 440 nm) (Monnier et ah, 1984 Pongor et ah, 1984). 

Al-Abed Y and Bucala R (1995) N-carboxymethyllysine formation by direct addition of glyoxal to lysine during the Maillard reaction. Bioorg Med Chem Lett 5, 2161-2162. 

Aside from the Maillard reaction, other covalent modifications of amino acids and proteins are possible within the caries lesion, which merit future investigation. For example, certain oral microorganisms excrete y-glutamyl transferases. These enzymes catalyse the formation of cross-links between glutamic acid and lysine residues of proteins. In addition, N-acyl amino acids are present in plaque, which adsorb to mineral surfaces. 

The initial Schiff base is digestible but after the Amadori rearrangement, the products are not metabolically available. Since lysine is the amino acid most likely to be involved and is an essential amino acid, Maillard browning reduces the biological value of proteins. Interaction of lysine with lactose renders the adjacent peptide bond resistant to hydrolysis by trypsin, thereby reducing the digestibility of the protein. 

The formation of brown pigments via the Maillard reaction, especially in model systems (e.g. glucose-glycine), usually follows zero-order kinetics, but the loss of reactants has been found to follow first- or second-order kinetics in foods and model systems. Activation energies of 109, 116 and 139 kJ mol-1 have been reported for the degradation of lysine, the formation of brown pigments and the production of hydroxymethylfurfural (HMF), respectively. 

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...

While the determination of total lysine is rather straightforward, the determination of free or available lysine is more problematic. In this situation, the term free is meant to imply that the e-amine of the lysine side chain has not reacted with various components of the sample matrix (most commonly carbohydrates via Maillard browning). This is important because reaction of the e-amine can render lysine nutritionally unavailable and the nutritive value for that protein is then diminished if lysine is the limiting amino acid (which is often the situation with soy proteins). While enzymatic digestion in the human gut may not release the modified lysine in a nutritionally available state, often these lysine adducts are labile to the standard acid hydrolysis in 6N HC1 at 110°C. This results in total lysine values that overestimate the amount of nutritionally available lysine. 

To study the effect of the Maillard reaction on nutritive value of protein, Patton, et a l. (57) heated purified casein and soybean globulin in 57. glucose solution for 24 hrs at 96.5°C, and found significant losses of lysine, arginine, tryptophan, and histidine (52). 

One of the earlier reviews (31 ) concerned the Maillard reaction in dried milk during storage. Spray-dried whey has considerable amounts of lactose and protein rich in lysine. Theoretical treatment of the problem in whey powder was the object of recent studies by Labuza and Saltmarch (106, 107). 

Milk-crumbs and soya-crumbs are new aroma sources produced by the Maillard reaction and intended to be used in the food industry. During the production of the crumbs thermal reactions take place in the material (e.g. milk) and the added glucose and amino acid constituents. Fructose-lysine and... 

Loss of Available Lysine in Protein in a Model Maillard Reaction System... 

Although the early Maillard reaction products are reported to have antioxidant properties and, in fact, can be utilized by processors to inhibit lipid oxidation in animal protein foods such as fish products, there is an accompanying lysine loss (4 5). 

Determination of Available Lysine by Various Procedures in Maillard-Type Products... 

In this report various chemical and in vivo methods are compared in their ability to assess nutritional damage in various model soya proteins representing mainly the Maillard-type modification of lysine. 

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