Thermal Denaturation and Gelation Characteristics of β-Lactoglobulin Genetic Variants

Abstract

The thermal characteristics of β-lactoglobulin (β-lg) genetic variants A and B were studied at pH 3.0, 5.0, 7.0 and 8.6 by differential scanning calorimetry (DSC). The β-lg B exhibited higher denaturation temperature and enthalpy than β-lg A and also denatured in a more cooperative fashion as indicated by a lower width at half-peak height. Fourier transform infrared spectroscopy (FTIR) was used to monitor changes in secondary structure of the two proteins when heated from 25 to 95°C. Results showed that β-lg A had a lower β-sheet content than the B variant at pH 3.0 and 5.0. At pH 7.0 and 8.6 the secondary structure of the two variants were similar. Aggregation bands (1682 cm -1 and ∼1622 cm -1) were observed when the proteins were heated at all pH values. The microstructure of gels made from 10% (w/v) solutions of β-lg A and B heated at 90°C for 30 min was studied by electron microscopy. The gel matrix of β-lg B at both acidic and alkaline pH was found to be made up of larger aggregates than the A variant. The aggregates of both variants were large (1-2 μm) and globular at acidic pH but much smaller (nanometer range) and amorphous at alkaline pH.