Induction of new physicochemical and functional properties by the glycosylation of whey proteins

Nucleophilic primary amino groups of whey proteins (beta-lactoglobulin and alpha-lactalbumin) were modified with reducing sugars in mild heat conditions. After 49 hr of heating (60 degrees C) at pH 6.5, 20-30% of beta-lactoglobulin amino groups were substituted with aldohexoses (galactose, mannose, glucose) and lactose, whereas up to 70% and 90% of beta-lactoglobulin amino groups were modified with ribose and glyceraldehyde, respectively. Gel electrophoresis and reversed-phase HPLC coupled with electrospray ionization mass spectrometry of glycosylated proteins indicated that the substitution was random. Consequently, highly heterogeneous families of glycosylated proteins were generated. Proteins substituted with hexoses and lactose exhibited higher solubility and improved emulsifying properties as compared with nonglycosylated proteins, in the whole pH range studied. In contrast, proteins glycosylated with ribose and glyceraldehyde showed lower solubility close to their isoelectric points. beta-Lactoglobulin modified with ribose and glyceraldehyde displayed substantial differences in denaturation behavior as compared with native protein. When compared with beta-lactoglobulin, glycosylation of alpha-lactalbumin was quicker. There was no difference in glycosylation yields nor rates of alpha-lactalbumin in presence and absence of calcium.