Influence of ultrasound pretreatment on the subsequent glycation of dietary proteins

The influence of ultrasound treatment on the subsequent glycation process of proteins is controversial. Glycation behaviors of bovine serum albumin (BSA), beta-lactoglobulin (beta-Lg) and beta-casein (beta-CN) after ultrasound pre-treatment (UP) were compared by both evaluating glycation kinetics and analyzing structural changes of proteins. UP resulted in both unfolding and aggregation behavior in protein samples, which altered the accessibility of the Lys and Arg. Five cycles of UP up-regulated the glycation degree of BSA and beta-Lg, possibly due to the unfolding behavior induced by UP, which exposed additional glycation sites. In contrast, 30 cycles of UP induced a dramatic increase (by 97.9 nm) in particle size of BSA, thus burying portions of glycation sites and suppressing the glycation process. Notably, UP had minimal influence on glycation kinetics of beta-CN, due to its intrinsic disordered structure. Based on proteomics analysis, the preference of Lys and Arg during glycation was found to be changed by UP in BSA and beta-Lg. Four, 3 and 3 unique carboxyethylated lysine residues were identified in glycated BSA after 0, 5 and 30 cycles of UP, respectively. This study suggests that the protein glycation can be affected by UP, depending on the ultrasonication duration and native structure of the protein.