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| - Molecular and Microstructural Studies of Thermal Denaturationand Gelation of β-Lactoglobulins A and B
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| - The thermal properties of β-lactoglobulins (β-lg) A and B at pH 3,5, 7, and 8.6 were studied bydifferential scanning calorimetry. Fourier transform infraredspectroscopy was used to monitorchanges in the secondary structure of the proteins when heated from 25to 95 °C. The microstructureof β-lg A and B gels made from 10% (w/v) protein solutions byheating at 90 °C for 30 min wasstudied by scanning and transmission electron microscopy. β-Lg Bhad greater thermal stabilityand required more energy to denature than β-lg A; denaturation ofβ-lg B was also more cooperative.Infrared spectroscopy showed that β-lg B had a higher proportionof β-sheet than the A variant atpH 3 and 5. At pH 7 and 8.6 the secondary structures of the twovariants were similar. At all fourpH values, aggregation bands (1682 and ∼1622cm-1) were observed when the proteins wereheated.Electron microscopy showed that the gel matrix of β-lg B at bothacid and alkaline pH was made upof larger aggregate structures than β-lg A. The aggregatesformed by both variants were large(1−2 μm) and globular at acid pH but much smaller (nanometer range)and amorphous at alkalinepH. This information provides a useful model for studying therelationship between protein structureand function. Keywords: β-Lactoglobulin; genetic variants; denaturation; gelation;differential scanning calorimetry; electron microscopy; infrared spectroscopy
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