ORIGINAL PAPER Comparison of Different Mechanical Methods for the Modification of the Egg White Protein Ovomucin, Part B: Molecular Aspects Janina Brand 1 & Ulrich Kulozik 1,2 Received: 3 August 2015 /Accepted: 29 February 2016 # Springer Science+Business Media New York 2016 Abstract It is indispensable to modify the physical properties of egg white prior to a fractionation of the included bio- functional 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 gener- ates comprehensive knowledge concerning the underlying mechanisms that enable the release of lysozyme as well as the use of egg white for fractionation processes. Keywords Egg white . Fibrillar protein ovomucin . Mechanical devices . Disrupture of protein bonds Introduction Based on its high protein content of around 90 % (ww -1 ) of the dry matter, egg white is a unique raw material that is often applied in food industry. Some of its proteins, like lysozyme and ovotransferrin, have bio-functional proper- ties, which makes them a target for separation processes. However, these fractionations, especially the large scale applications, are limited because of the physical properties of egg white. In particular, the highly viscous, gel-like structure and the inhomogeneous distribution of different viscosities within the egg white that are both caused by the fibrillar protein ovomucin. Ovomucin is a filamentous biopolymer that is cross-linked through disulfide bridges, whereby it builds a network structure (Donovan et al. 1970; Rabouille et al. 1990; Ternes et al. 1994; Strixner and Kulozik 2011). At neutral pH or in the absence of denaturing agents, ovomucin is highly insoluble (Omana et al. 2010b). The protein itself consists of two subunits α-ovomucin and β-ovomucin that differ in their physical characteristics (e.g., molecular weight, amino acid com- position etc.) (Itoh et al. 1987; Hayakawa and Sato 1978; Robinson and Monsey 1971 ; Hiidenhovi 2007 ). Ovomucin is also responsible for the low availability of free lysozyme, which limits the fractionation of this func- tional protein. This is on the one hand due to the ovomucin network structure in combination with the small size of the protein lysozyme (14.3 kDa). The net- work structure leads to water embeddings, in which this small molecule is entrapped (Brand et al. 2014). On the other hand, lysozyme has a high isoelectric point of 10.7, * Janina Brand janina.brand@tum.de 1 Chair for Food Process Engineering and Dairy Technology, Technische Universität München, Weihenstephaner Berg 1, 85354 Freising, Germany 2 ZIEL Institute for Food and Health, Technische Universität München, Weihenstephaner Berg 1, 85354 Freising, Germany Food Bioprocess Technol DOI 10.1007/s11947-016-1711-4