A Comparison of the Structure of β-Lactoglobulin Aggregates Formed at pH7 and pH2

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Abstract
In order to investigate the influence of electrostatic interactions on the thermal aggregation of β-lactoglobulin, different conditions of pH and ionic strength were used. Some structural features of the aggregates over a broad spatial range were determined with the use of scattering techniques. In the case of pH7, a first step of the aggregation process, leading to particles of about 60 monomers (which we refer to as ‚globules‘), occurs whatever the ionic strength. Depending on the degree of screening, further aggregation can take place, leading to the formation of self-similar aggregates with fractal dimension 2.0. At pH7, both hydrophobic interactions and interchange of disulphide bonds could be involved. At pH2, the very low reactivity of the sulfhydric group may inhibit the formation of the globules. The aggregates are locally more or less rod-like and exhibit again fractal behaviour at larger distances, with a fractal dimension depending on the degree of screening. The influence of the ionic strength on the branching of the aggregates is also discussed.