Effect of molecular size and charge state of reducing sugars on nonenzymatic glycation of β-lactoglobulin

•A larger molecular size of reducing sugars would reduce the glycation extent.•The negative charge state would reduce the glycation extent.•Glucose and its oligomers differed on K 8, 70 and 75 of β-lg during glycation.•Galactose and galacturonic acid differed on K 77 of β-lg during glycation.

This study was to investigate the effect of molecular size and charge state of reducing sugars on the nonenzymatic glycation of β-lactoglobulin (β-lg), with emphasis on the variation in glycation extent and glycation site. Five sugars (glucose, galactose, galacturonic acid, maltose and maltotriose) were selected to react with β-lg in dry-state (aw at 0.53, 45 °C) and the glycated products were analyzed by liquid chromatography-mass spectrometry (LC-MS) and data-independent acquisition LC-MS (LC-MSE). The results showed that increasing molecular size and negative charge state of reducing sugars would reduce the glycation extent. In addition, the difference of molecular size would result in the variation of glycation on the site of K 8, 70 and 75, and the negative charge state would lead to dissimilarity of glycation on K 77 of β-lg. The analysis of the glycation sites was based on the fragmentation behaviors of the reducing sugars proposed according to the deconvoluted MSE spectra. Among the five reducing sugars, glucose and galactose had the same dissociation pathway. Galacturonic acid had a distinctive dissociation behavior with a neutral loss of 98. Maltose and maltotriose were comparable to glucose but more complex.