Maillard glycation of $\beta$-lactoglobulin with several sugars: comparative study of the properties of the obtained polymers and of the substituted sites

Abstract

Maillard reactions represent a major cause of structural and chemical modifications of proteins during industrial food processing and storage. Nutritional and functional properties of food proteins are highly dependent on this reaction. A better knowledge of this modification and of its structural consequences presents a great interest for the food industry. In this study, β-lactoglobulin was heated in solution at 60 o C in the presence of arabinose, galactose, glucose, lactose, rhamnose and ribose. Protein polymerization and glycation site specificity were investigated according to the nature of sugar used for modification of β-lactoglobulin. Among the six common sugars used, arabinose and ribose induced the highest degree of modification. Glucose, galactose and rhamnose were less reactive and lactose generated the lowest degree of modification. Proteins substituted with ribose or arabinose formed polymers stabilized by sugar induced covalent bonds. When other sugars were used, part of the aggregated proteins were stabilized only by hydrophobic interaction and disulfide bonds. The site specificity for the attachment of each sugar could not be clearly demon- strated. According to mass spectrometry analysis, leucine 1 (N-teminal amino acid), lysine 14 and lysine 47 were modified in the presence of galactose, glucose or lactose. Lysines 69, 75 and 135 were modified only in the case of protein glycated with glucose. Lysine 100 was modified only when pro- tein was glycated with lactose. No glycation site could be detected for proteins glycated with ribose or arabinose due to the higher degree of modification and polymerization which inhibited the tryptic hy- drolysis used before mass spectrometry analysis.