Erika Silletti

Identification of salivary proteins at oil–water interfaces stabilized by lysozyme and β-lactoglobulin

In this research, we investigated the interaction occurring between oil-in-water emulsion droplets, stabilized by different emulsifiers, i.e. lysozyme and beta-lactoglobulin (beta-lg), and salivary proteins (SPs) with a molecular mass (M(r)) above about 10kDa. Different techniques, i.e. infrared spectroscopy, Western blotting, PAS staining and SDS-PAGE coupled to MS, were employed for this purpose. This study demonstrated the interaction between several salivary proteins and the emulsifiers at the oil-water interfaces. In particular, results show that the high M(r) mucin MUC5B was strongly bound to lysozyme stabilized emulsions, whereas beta-lg stabilized emulsions associated with MUC7 and, moderately, with MUC5B. Furthermore, we observed that salivary proteins in the range M(r) 10-100kDa associated differently with emulsion droplets. A large majority of SPs was found to interact with lysozyme stabilized emulsion droplets whilst in case of beta-lg stabilized emulsions, the SPs distribute more evenly between the fraction associated and non-associated with the droplets. A clear example is alpha-amylase (M(r) approximately 55kDa) which predominantly associates with lysozyme stabilized emulsion droplets, but not with beta-lg emulsion droplets. To conclude, our findings indicate that adsorption/association of salivary protein components onto the emulsion droplets is related to the type of emulsifying proteins at the oil-water interfaces and it is probably driven by the overall net charge at the droplets oil-water interfaces, i.e. positive for lysozyme stabilized emulsions and negative for beta-lactoglobulin stabilized emulsion at neutral pH.

Characterizing Length Scales that Determine the Mechanical Behavior of gels from Crosslinked Casein Micelles

Mechanical behavior of a protein gel plays a large role in sensory properties. Despite the large amount of research on caseins, the origin of the mechanical behavior is not well understood yet. To determine the length scales that are relevant for the mechanical behavior of casein gels, casein micelles were crosslinked with increasing amount of transglutaminase followed by acidification to form gels. The gel heterogeneity, observed with confocal microscopy, electron microscopy and light scattering showed a gradual decrease on a micrometer length scale with increasing crosslinking. Such gradual change as a function of crosslinking was also observed in the elastic modulus and the Young’s modulus of the gels. Furthermore, particle size both prior to gelation and in the gel decreased with increasing crosslinking. Casein micelle stiffness (determined by atomic force microscopy) showed a maximum and the amount of water entrapped by the gel particles and their aggregates in the gel (determined by neutron scattering) showed a minimum with increasing crosslinking. These extrema coincides with the extrema observed in kinetics of gel formation and in gel breakdown properties. It was concluded that the elasticity of the gel originates on the length scale of the casein micelle (a few hundred nanometer), while fracture properties are determined at a smaller length scale, by the structure within the casein micelle.

Saliva-induced emulsion flocculation: role of droplet charge

Human saliva is a complex heterogeneous biological fluid composed of proteins, electrolytes, small organic compounds and water.1–3 It is involved in several functions in the oral cavity and is responsible for maintaining oral health and for protection of the teeth and mucosal surfaces.4 Mixing with ...