Updated project metadata. Here we studied the glycation of bovine milk proteins by lactose as dominant sugar in milk and hexoses using tandem mass spectrometry (CID and ETD mode). In a bottom-up proteomics approach after enriching glycated peptides by boronate affinity chromatography, first we could identify 260 lactosylated peptides corresponding to 124 lactosylation sites in 28 bovine milk proteins in raw milk, raw colostrum, three brands of pasteurized milk, three brands of UHT milk, and five brands of infant formula. The same regular and additionally two lactose-free milk products (pasteurized and UHT milk) where lactose is enzymatically cleaved into the more reactive hexoses were analyzed in terms of hexosylation sites that resulted in identification of 124 hexosylated tryptic peptides corresponding to 86 glycation sites in 17 bovine milk proteins. In quantitative terms glycation increased from raw milk to pasteurized milk to UHT milk and infant formula, i.e., with the harsher processing conditions. Lactose-free milk contained significantly higher hexosylation degrees than the corresponding regular milk product.