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Neufahrn bei Freising, Germany

Gebhardt R.,Weihenstephaner Berg | Toro-Sierra J.,Weihenstephaner Berg | Kulozik U.,Zentralinstitut For Ernahrungs Und Lebensmittelforschung
Soft Matter | Year: 2012

We study pressure dissociation of aggregated states of β-lactoglobulin at pH 4.6 using static and dynamic light scattering. We find that octamers dissociate at 20°C into dimers at pressures P < 100 MPa and into monomers at P < 200 MPa. The dimer-monomer dissociation equilibrium at T = 20°C is reversible. The dodecamer-dimer equilibrium is quasi-reversible since aggregation occurred after decompression from 30 MPa back to ambient pressure. The corresponding molar volume difference is ΔV = 101 ml mol-1 for the octamer-dimer and ΔV = 276 ml mol-1 for the dimer-monomer transition. The calculated free energy of association for the dimers at atmospheric pressure is ΔG = -59.3 kJ mol-1 and for the monomers is ΔG = -59.8 kJ mol-1. The high pressure dissociation is not emphasized by lowering the temperature. Instead, the quaternary structure of β-lactoglobulin at T = 10°C remains unchanged up to pressures of P = 180 MPa followed by aggregation at pressures P > 180 MPa. This journal is © 2012 The Royal Society of Chemistry.

Gebhardt R.,Weihenstephaner Berg | Steinhauer T.,Weihenstephaner Berg | Meyer P.,Weihenstephaner Berg | Sterr J.,Lehrstuhl fur Lebensmittelverpackungstechnik | And 2 more authors.
Faraday Discussions | Year: 2012

Casein micelles undergo shape changes when subjected to frontal filtration forces. Grazing incidence small angle X-ray scattering (GISAXS) and atomic force microscopy (AFM) allow a quantification of such structural changes on filtration cakes deposited on smooth silicon micro-sieves. A trans-membrane pressure of Δp = 400 mbar across the micro-sieve leads to an immediate film formation after deposition of casein solution. We observe significant changes in the GISAXS pattern depending on how many layers are stacked on top of each other. Compared to a deposit formed by one layer, GISAXS on a deposit formed by three layers of casein micelles leads to less scattering in the vertical and more scattering in the horizontal direction. Simulations show that the experimental results can be interpreted by a structural transformation from an originally spherical micelle shape to an ellipsoidal-deformed shape. The results are supported by AFM measurements showing a reduced lateral size of casein micelles deposited on top of a membrane pore. The observed shape changes could be due to filtration forces acting on densely packed deposits confining the micelles into ellipsoidal shapes. © 2012 The Royal Society of Chemistry.

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