Hen egg yolk's main fractions, granules and plasma contribute to the formation and the stability of disperse systems like emulsions by constituting an interfacial film. However, yolk is still used empirically and physical properties of yolk fractions are not entirely understood. Therefore, one of the main approaches is to fractionate egg yolk in its single components and to close the lack of understanding of the molecular and structural characteristics of each fraction. As our sedimentation experiments show, separation efficiency of granules from hen egg yolk varies with changing solution pH. Under isoelectric conditions at pH 4.0, granules bind more low density lipoprotein (LDL; plasma-fraction), as atomic force microscopy reveals. We show that besides reduced electrostatic repulsion forces also structural changes of the granules support a higher incorporation of LDL-vesicle at pH 4.0. Varying amounts of lipid with pH make a structural analysis difficult by imaging techniques alone. We report on X-ray scattering experiments in reflection geometry performed on films of henegg granules. The observed scattering patterns provide prominent lateral distances in the film and a repeating distance from the phospholipids of the LDL vesicles. At pH 4.0 the repeating distance is larger and less diffuse compared to pH 6.5. We extracted two prominent lateral particle sizes in the HDLgranule film from two significant shoulders in the scattering functions. At pH 4.0 the obtained radii of gyration are Rg 1 = 83 nm and Rg 2 =2.4 nm. At pH 6.5 we observed a significant expansion of both sizes. This indicates rougher contact areas and a stronger steric hindering for the incorporation of the LDL vesicle in the HDL-granules under native milieu conditions.

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 deltap = 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.

Today, flexible vacuum packages are predominantly used for products to be subjected to high pressure treatment. However, tray packages with a modified atmosphere are in demand, which provide a high failure rate with respect to gas and water vapour permeability and packaging integrity. Methods to follow permeation processes under high pressure were developed and used together with optical microscopy, confocal scanning laser microscopy, Raman spectroscopy and atomic force microscopy to identify the mechanisms for changes in permeability and damage to the packaging materials. Single film samples and pouch packages filled with model products were studied. Results indicate a reversible decrease in the coefficients of diffusion and permeation under the impact of high pressure, due to the compression of the polymeric bulk. Irreversible changes in the polymeric materials are associated with gases in the packaging head space, which cause high local temperatures and create damage due to rapid deliberation upon the pressure drop at the end of the high pressure cycle

As high‐pressure processing is used increasingly for the treatment of packed products, different packaging has been investigated with respect to their structural behaviour and stability under high‐pressure processing. Often, failures and changes of the polymeric structure occur. Common damage symptoms of high‐pressure‐treated packaging materials are defined and classified in this review. These damage symptoms are allocated to the physico‐chemical effects that created them. The effects may be separated into direct effects induced by the action of the high‐pressure alone and indirect effects that are mediated via compressed contents of the package, i.e. filled product and gaseous headspace. The direct effects split up again in reversible and irreversible structural changes. The indirect effects are generated by compressed headspace gases, other compressed substances and the consequences of increased amounts of gases dissolved in the polymers. If applicable, current theoretical approaches have been allocated to the different categories of damage. Copyright © 2013 John Wiley & Sons, Ltd.