DETECTION OF INTERMEDIATE OLIGOMERS, IMPORTANT FOR THE FORMATION OF HEAT AGGREGATES OF BETA-LACTOGLOBULIN

The early stages of heat induced aggregation of beta-lactoglobulin A, B and A/B from different sources have been studied by combined static light scattering and HPLC and by dynamic light scattering. The heat ag gregation experiments were carried out at 67.5 degrees C using 10 mg m L-1 beta-lactoglobulin at pH 6.8 in 10 mM phosphate buffer and 60 mM NaCl. Before heating (20 degrees C) more than 90% of beta-lactoglobuli n is present as dimers. Even after 15 min heating at 67.5 degrees C mo re than 90% of beta-lactoglobulin is present in dimeric form. Various amounts of the monomer are present both before and during heating in a ll samples but never more than 5% of the total beta-lactoglobulin. In the period before the large aggregates are detected oligomers (up to p entamers) are built with increasing percentage. Hereafter the oligomer s gradually decrease in percentage as a function of time. Both the A a nd B variant of beta-lactoglobulin shows the same behaviour of forming intermediate oligomers after heating. Of these trimers are dominating . This suggests that the monomer is involved in oligomer formation in spite of its low abundance, possibly explained by a high turnover of m onomers into oligomers. However, they differ in the type of oligomers produced after heating. Where the A variant primarily builds pentamers , the B variant primarily builds tetramers. The correlation found betw een the presence of intermediate oligomers and initiation of heat aggr egation could be important information to include in existing and futu re models of heat aggregation kinetics of beta-lactoglobulin. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.