Glycation leads to polymerization and tryptic resistance of beta-lactoglobulin
Résumé
The Maillard reaction also named “non-enzymatic browning” is a chemical reaction involving reducing sugars and the amino groups of amino acids and proteins. Despite its great importance in culinary art thanks to generation of flavors this reaction may be also deleterious because of uncontrolled deterioration of foods during storage and processing. The aim of this work was to determine how the time of heating of ßlactoglobulin, at 60°C, in the presence of glucose, could influence the modification of this most important whey protein. Upon heating, glycation induced the polymerization of b-lactoglobulin via non S-S bond; molecular masses of about 18, 36 and 55 kDa could be observed in SDS-PAGE. The grafting of glucose on lysine and arginine (the most modified amino acids on the protein) led to a shift of the pHi of the modified proteins toward acidic pH (IEF) and to a resistance to tryptic attack (RP-HPLC). The Maillard reaction between b-lactoglobulin and glucose makes modified proteins resistant to trypsinolysis. Consequently, glycation may affect the nutritional properties of this whey protein. However, since the amino acids involved in ligand binding are not glycated, this implies their shielding by spatial factors and/or possible internalized ligands.
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