Influence of the ionic strength on the heat-induced aggregation of the globular protein β-lactoglobulin at pH 7

The influence of the ionic strength on the structure of beta-lactoglobulin aggregates formed after heating at pH 7 has been studied using static and dynamic light scattering. The native protein depletion has been monitored using size exclusion chromatography. Above a critical association concentration (CAC) well-defined clusters are formed containing about 100 monomers. The CAC increases with decreasing ionic strength. The so-called primary aggregates associate to form self similar semi-flexible aggregates with a large scale structure that is only weakly dependent on the ionic strength. The local density of the aggregates increases with increasing ionic strength. At a critical gel concentration, C-g, the size of the aggregates diverges. C-g decreases from 100 g/l without added salt to 1 g/l at 0.4 M NaCl. For C > C-g the system gels except at high ionic strength close to C-g where the gels collapse under gravity and a precipitate is formed. (C) 2003 Elsevier B.V. All rights reserved.