ADSORPTION DURING HEAT-TREATMENT RELATED TO THE THERMAL UNFOLDING AGGREGATION OF BETA-LACTOGLOBULIN-A AND BETA-LACTOGLOBULIN-B

Adsorption onto chromium surfaces during heat treatment (65-68 degrees C) of beta-lactoglobulin A and B in phosphate buffer, pH 6.88, was in vestigated by in situ ellipsometry. Thermal unfolding and in situ heat -induced aggregation under the same conditions were studied by differe ntial scanning calorimetry and dynamic light scattering, respectively. A lag phase was observed for buildup of the thickness of the adsorbed layer of beta-lactoglobulin A and B at 68 degrees C. The lag period w as found to increase with decreasing temperature, The difference in ad sorption rate between the variants was found to be in agreement with t he aggregation difference in solution, that is, the A variant aggregat ed more rapidly after a somewhat slower beginning. These results could be related to a difference in the thermal unfolding behavior, By appl ying a non-two state model the second of two transitions was suggested to involve the activation of the free sulfydryl group. The results in dicated that fouling proceeds via attachment of aggregates with an act ivated free sulfydryl group through an interchange reaction with a dis ulfide bond in the adsorbed protein layer. (C) 1996 Academic Press, In c.