Polymerization of Lysozyme and Impairment of Its Amino Acid Residues Caused by Reaction with Glucose

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Abstract
Browning alterations are probably caused by Maillard reactions between proteins and reducing sugars. In order to reveal the mechanism of the Maillard reaction between proteins and reducing sugars, unmodified and chemically modified lysozymes were incubated with and without glucose at 50.degree. C and 75% relative humidity in the solid state. Incubation of unmodified lysozyme with glucose resulted in browning and polymerization of the protein, and noticeable losses of Arg, Lys and Trp residues. Those changes were little affected by the presence of an O adsorber. Acetylation of lysozyme almost completely prevented those changes, indicating that the reaction of free amino groups of the protein with glucose was essential at the initial stage of these changes. Incubation of lysozyme with Arg residues masked with 1,2-cyclohexanedione (CHD) resulted in almost the same changes as above even in the absence of glucose. Those changes were probably caused by the action of CHD released from the Arg residues. This similarity in the effects on protein of CHD and glucose implied that dicarbonyl compounds were key components at the secondary stage of the Maillard reaction between proteins and reducing sugars.