Egg white (EW) is required to be reduced in viscosity and particle size prior to chromatographic fractionation of single EW proteins. This study reports on an assessment of various shear devices for this purpose. Evaluation criteria for the head-to-head comparison of high-pressure homogenization, colloid mill, and toothed disc dispersing machine treatment were the achieved viscosity reduction as well as the network diminution, determined by particle size measurements. It was shown that each of the devices was able to decrease the viscosity by a reduction of fibril size. However, only the high-pressure homogenizer fulfills the requirement to disintegrate the fibrils sufficiently, so that they can be filtered through membranes with a pore size of 0.45 μm, which is indispensable for chromatographic fractionations. Generally, the achieved viscosities decreased with increasing energy input, independently of the specific shear forces resulting from the applied device. Otherwise, there was no direct correlation between the energy density and the extent of fibril destruction, indicating that the kind of energy depending on the respective device with its specific destruction mechanism was not decisive. To sum up, this study provides profound knowledge concerning the effects on the EW structure that result from different mechanical forces.
It is indispensable to modify the physical properties of egg white prior to a fractionation of the included biofunctional proteins. It was already demonstrated that this can be realized with mechanical devices. However, until now, it was not clear by which kind of molecular changes this is accompanied. Thus, this study reports on the molecular changes in egg white proteins induced by various mechanical treatments (high-pressure homogenizer, colloid mill, toothed disc dispersing machine). Evaluation criteria were the particle size of the long-chain protein ovomucin, the content of thiol groups, and disulfide bridges in egg white as well as the amount of free lysozyme. In general, it was shown that these treatments led to changes in the molecular structure and that the obtained modifications were more pronounced the higher the applied energy was. In detail, it was found that the applied mechanical forces in the experimental range of this study were able to disrupt strong covalent bonds in the fibrillar protein ovomucin. Additionally, the bio-functional protein lysozyme that is partly entrapped in the natural egg white structure was released by the applied forces. Summing up, this study generates comprehensive knowledge concerning the underlying mechanisms that enable the release of lysozyme as well as the use of egg white for fractionation processes.
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