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

Maillard reactions represent a major cause of structural and chemical modif ications of proteins during industrial food processing and storage. Nutriti onal and functional properties of food proteins are highly dependent on thi s reaction. A better knowledge of this modification and of its structural c onsequences presents a great interest for the food industry. In this study, beta -lactoglobulin was heated in solution at 60 degreesC in the presence of arabinose, galactose, glucose, lactose, rhamnose and ribose. Protein pol ymerization and glycation site specificity were investigated according to t he nature of sugar used for modification of beta -lactoglobulin. Among the six common sugars used, arabinose and ribose induced the highest degree of modification. Glucose, galactose and rhamnose were less reactive and lactos e generated the lowest degree of modification. Proteins substituted with ri bose or arabinose formed polymers stabilized by sugar induced covalent bond s. When other sugars were used, part of the aggregated proteins were stabil ized only by hydrophobic interaction and disulfide bonds. The site specific ity for the attachment of each sugar could not be clearly demonstrated. Acc ording to mass spectrometry analysis, leucine 1 (N-teminal amino acid), lys ine 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 protein was glycat ed with lactose. No glycation site could be detected for proteins glycated with ribose or arabinose due to the higher degree of modification and polym erization which inhibited the tryptic hydrolysis used before mass spectrome try analysis.