Effect of glycation on the structural modification of β-conglycinin and the formation of advanced glycation end products during the thermal processing of food

Glycation often occurs during the thermal processing of food, and may result in changes to the structure of proteins and decreases in nutritional value. A model system consisting of β-conglycinin and sugars (d-glucose, lactose) was used to investigate the effects of glycation on the structure of β-conglycinin and the formation of advanced glycation end products during the thermal processing of food. The results show that both d-glucose and lactose can modify β-conglycinin during thermal processing, including during boiling, sterilizing, and baking. As the degree of thermal processing increased, the molecular weight of glycated β-conglycinin increased significantly, and the secondary structure gradually changed from α-helix and β-sheet structures to random coil. The contents of free lysine (Lys) and arginine (Arg) residues in glycated β-conglycinin decreased along with the formation of protein-bound Ne-(carboxymethyl)lysine (CML) and Ne-(carboxyethyl)lysine (CEL). In addition, the major types of modification indicated by high-resolution mass spectrometry were d-glucose adduct, CML and CEL on Lys residues, and methylglyoxal-derived hydroimidazolone on Arg residues. The higher processing temperatures resulted in greater numbers of modification sites and greater contents of protein-bound AGEs.