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

A model Maillard reaction system was developed to measure the loss of available lysine in a pure protein system after reaction with two keto-aldehydes normally present in food systems. Bovine plasma albumin and malonaldehyde or methylglyoxal reactions were measured in an aqueous solution. Conditions of reaction were varied over a range representative of conditions during handling and storage of food. pH was adjusted between 5 and 8. Temperatures in the range 20-60°C were tested. Reactant concentrations of 0.07 to 35.0 mM carbonyl compound and 1 to 10 g/L albumin were used. Loss of available lysine was measured by a trinitrobenzenesulfonic acid method for residual lysine. With malonaldehyde, loss of available lysine decreased as pH increased, but with methylglyoxal, an increased pH increased the lysine loss. Both carbonyl compounds caused significant increasing loss of lysine with increasing temperature and concentration. Results indicated that methylglyoxal reacts with protein to effect a loss of available lysine, but more slowly than does malonaldehyde. Temperature had the greatest effect on lysine loss, but the concentration of the carbonyl compound and the pH of the reaction mixture also influenced the rate.