Association behavior of native β-lactoglobulin

The association behavior of β‐lactoglobulin has been studied by small‐angle neutron scattering as a function of protein concentration, temperature, pH, and NaCl concentration of the solution. By indirect Fourier transformation of the spectra, pair‐distance distribution functions for the various samples were obtained. These functions provided information on the maximum size, the weight‐averaged molecular mass, and the z‐averaged radius of gyration of the β‐lactoglobulin particles. At room temperature and pH values below 4 and above 5.2 the protein consists predominantly of monomers and dimers, consistent with literature. In these pH regimes the formation of dimers is favored upon increasing ionic strength and decreasing protein charge (pH values closer to the isoelectric point of the protein). Around pH 4.7, larger oligomeric structures are formed, enhanced by a decrease in temperature and a decrease in ionic strength. β‐Lactoglobulin A associates more strongly than β‐lactoglobulin B. Surprisingly, at pH 6.9 larger structures than dimers seem to be formed at high protein concentrations (>30 mg mL−1). © 1999 John Wiley & Sons, Inc. Biopoly 49: 11–20, 1999