LACTOLATION OF BETA-LACTOGLOBULIN MONITORED BY ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY

Direct monitoring of the Amadori product formation between lactose and beta-lactoglobulin was performed by electrospray ionisation mass spec trometry. As expected, the glycation reaction was faster at low water activity than in aqueous system. Heterogeneous beta-lactoglobulin glyc oforms were observed, with different number of lactose bound: populati ons of beta-lactoglobulin with 1 to 7 and 2 to 11 linked lactose were detected, respectively, after 10 and 22 h of reaction under 65% relati ve humidity and 50 degrees C. Trypsinolysis of glycated proteins, foll owed by reverse-phase HPLC coupled to tandem mass spectrometry in the neutral loss scanning mode, indicated that all potential reactive amin o groups, except Lys(101), were involved in sugar binding. The resulti ng order of reactivity, as a function of reaction time, was as follows : Lys(74,91) > alpha-amino-group, Lys(15,70,100) > Lys(60,69,75,77,83, 135,138) > Lys(8,141). (C) 1998 Elsevier Science Ltd. All rights reser ved.