Functional properties of milk proteins glycated in mild conditions

Nucleophilic primary amino groups of milk proteins (beta-lactoglobulin and beta-casein) were modified with reducing sugars in mild heat conditions. Af ter 3 d of heating (60 degrees C) under anaerobic conditions at pH 6.5, 20% to 30% of beta-lactoglobulin or beta-casein amino groups were substituted with aldohexoses (galactose, rhamnose, glucose) and lactose, whereas up to 40% and 70% of beta-lactoglobulin or beta-casein amino groups were modified with arabinose and ribose, respectively. Glycation was also carried out at 45 and 34 degrees C. Polyacrylamide gel-electrophoresis indicated generati on of highly heterogeneous families of glycated proteins. beta-Lactoglobuli ns substituted with most of the hexoses, and lactose exhibited higher solub ility as compared with healed non-glycated protein, in the whole pH range s tudied. Glycation with aldopentoses induced lower glycated protein solubiti ty, especially in the neighbourhood of their isoelectric paints, independen tly of the reducing sugar studied, the emulsifying properties of glycated p roteins were improved as compared with heated non-glycated beta-lactoglobul in. After lactosylation, the emulsifying activity was higher than that meas ured without any treatment. Solubility of glycated beta-caseins was only hi gher in the pH range 4-6. This may be explained by the shift of the isoelec tric points of the derivatives produced. The emulsifying activity of beta-c asein was unchanged after glycation.