Abstract
This study aimed to compare the effects of high intensity ultrasound (HIU) applied at various amplitudes (20~40%) and for different durations (1~10 min) on the physiochemical and structural properties of goat milk β-lactoglobulin. No significant change was observed in the protein electrophoretic patterns by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Deconvolution and second derivative of the Fourier transform infrared spectra (FTIR) showed that the percentage of β-sheet of goat milk β-lactoglobulin was significantly decreased while those of α-helix and random coils increased after HIU treatment The surface hydrophobicity index and intrinsic fluorescence intensity of samples was enhanced and increased with increasing HIU amplitude or time. Differential scanning calorimetry (DSC) results exhibited that HIU treatments improved the thermal stability of goat milk β-lactoglobulin. Transmission electron microscopy (TEM) of samples showed that the goat milk β-lactoglobulin microstructure had changed and it contained larger aggregates when compared with the untreated goat milk β-lactoglobulin sample. Data suggested that HIU treatments resulted in secondary and tertiary structural changes of goat milk β-lactoglobulin and improved its thermal stability.
Highlights
Introduction βLactoglobulin is a major whey protein in ruminant milk (~50%, w/w)
Different retention times between bovine and goat milk β-lactoglobulin may be due to the different molecule polarity
Compared with bovine milk β-lactoglobulin, eight different amino acids were found in goat milk β-lactoglobulin molecule primary structure, which may lead to a slightly different polarity
Summary
Lactoglobulin is a major whey protein in ruminant milk (~50%, w/w). It mainly exists in the form of a dimer at its physiological pH [1]. Β-lactoglobulin monomer is a compact molecule with a molecular weight at 18.3 kDa. It mainly exists in the form of a dimer at its physiological pH [1]. Studies showed that β-lactoglobulin molecule contains nine β-sheets and one α-helix [3] For bovine milk, this protein has a shape of a “calyx”, which was composed of eight β-sheets and the ninth β-sheet forms a part of the β-lactoglobulin dimer interface [4,5]. High similarity in sequence between bovine and Molecules 2020, 25, 3637; doi:10.3390/molecules25163637 www.mdpi.com/journal/molecules
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