LYSINE LOSS AND POLYMERIZATION OF BOVINE BETA-LACTOGLOBULIN BY AMINO CARBONYL REACTION WITH LACTULOSE (4-O-BETA-D-GALACTOPYRANOSYL-D-FRUCTOSE)

Loss of lysine, protein polymerization, and production of fluorescent substances were investigated for bovine beta-lactoglobulin stored with lactulose (4-O-beta-D-galactopyranosyl-D-fructose) at 50-degrees-C and 65% relative humidity for 10 days as a model system for dried milk and milk products supplemented with lactulose. Reactivity of lactulose with protein amino groups was much lower than that of lactose, whereas the lactulose induced the protein polymerization and production of fluorescent substances not less strongly than lactose did. These results suggested that the effect of the amino carbonyl reaction between lactulose and milk proteins on protein nutritive value, i.e., lysine loss, was not very serious but that proteins reacted with lactulose were easily polymerized by cross-linking through lactulose-lysine amino carbonyl adducts.