Cohesiveness and flowability of particulated solid and semi-solid food systems.

Cohesiveness and flowability of particulated food systems is of particular interest in the oral processing and swallowing of food products, especially for people suffering from dysphagia. Although cohesiveness of a bolus is an essential parameter in swallowing, a robust technique for objective measurement of cohesiveness of particulated semi- or soft-solids is still lacking. In our approach the ring shear tester is used to measure the cohesiveness and flowability of a model particulated food system based on fresh green pea powders and pastes with controlled moisture content. The focus is on how the cohesiveness and flowability of dry pea particles change as they absorb moisture, swell and soften, while continuously agglomerating until a paste like bolus is achieved. Differently hydrated pea powders start to granulate with increasing moisture content resulting in decreasing flowability and increasing cohesiveness until a critical moisture content of approximately 73 wt% is reached. Above the critical moisture content, cohesiveness starts to decrease and flowability increases, i.e. indicating the transition into the rheological domain of concentrated suspension flow. Besides moisture content we also show that water adsorption capacity i.e. hydration properties and resulting degree of particle softness tremendously influences the flowability factor and cohesiveness of powder systems. Thus ring shear tester can be used to provide guidelines for food paste formulation with controlled cohesiveness.

Scaffold requirements for periodontal regeneration with enamel matrix derivative proteins.

Periodontitis affects the attachment of natural teeth, and infection or inflammation associated with periodontitis may affect peri-implant tissues. Enamel matrix derivative (EMD) proteins provide stimulation for self-regeneration of the damaged tissue when applied to wide intrabony defects as part of a mixture with bone graft material. As a first step of the process enhancing cell proliferation and ligament formation, we demonstrated that EMD protein precipitation depends strongly on the physical and chemical characteristics of the bone grafts used in the mixture. To guarantee optimum protein-stimulated self-regulation, the pH of the initial EMD formulation must therefore be adjusted between 3.9 and 4.2 in order to compensate the change in pH induced by the bone graft. Moreover, the interaction between the two components resulted in precipitates of different shape and size differently covering the grafts. This outcome might potentially have clinical implications on cell attachment and periodontal ligament extension, which deserve further in vitro and in vivo tests.

Kinetics of Oil Exchange in Nanoemulsions Prepared with the Phase Inversion Concentration Method.

Nanoemulsions (NEs) are metastable emulsions with droplet sizes between 20 and 100 nm and with a wide range of applications, for example, in polymerization, in pharmaceutical and cosmetic formulations, and as drug delivery systems. Even though they are not in thermodynamic equilibrium, they can be metastable over relatively long times and have the advantage that they can be formed easily by low energy input methods. In particular, the phase inversion concentration (PIC) method allows the formation of NEs by the dilution of a suitable mixture of oil and surfactants with water. In this paper, we investigate the kinetics of the oil exchange process of NEs formed by the PIC method by looking at the exchange of different hydrophobic oils and by employing contrast variation stopped flow small-angle neutron scattering. These experiments demonstrate that this exchange becomes substantially slower by increasing the chain length of the alkane. This indicates a mechanism where monomer exchange is relevant, which would indicate also that for aging one would expect Ostwald ripening to be the determining factor. Such investigations can be carried out in a unique fashion by means of neutron scattering, and the results have important implications for the optimization of NE formulations.

The Influence of Arginine on the Response of Enamel Matrix Derivative (EMD) Proteins to Thermal Stress: Towards Improving the Stability of EMD-Based Products.

In a current procedure for periodontal tissue regeneration, enamel matrix derivative (EMD), which is the active component, is mixed with a propylene glycol alginate (PGA) gel carrier and applied directly to the periodontal defect. Exposure of EMD to physiological conditions then causes it to precipitate. However, environmental changes during manufacture and storage may result in modifications to the conformation of the EMD proteins, and eventually premature phase separation of the gel and a loss in therapeutic effectiveness. The present work relates to efforts to improve the stability of EMD-based formulations such as Emdogain™ through the incorporation of arginine, a well-known protein stabilizer, but one that to our knowledge has not so far been considered for this purpose. Representative EMD-buffer solutions with and without arginine were analyzed by 3D-dynamic light scattering, UV-Vis spectroscopy, transmission electron microscopy and Fourier transform infrared spectroscopy at different acidic pH and temperatures, T, in order to simulate the effect of pH variations and thermal stress during manufacture and storage. The results provided evidence that arginine may indeed stabilize EMD against irreversible aggregation with respect to variations in pH and T under these conditions. Moreover, stopped-flow transmittance measurements indicated arginine addition not to suppress precipitation of EMD from either the buffers or the PGA gel carrier when the pH was raised to 7, a fundamental requirement for dental applications.

Self-aggregation of mixtures of oppositely charged polyelectrolytes and surfactants studied by rheology, dynamic light scattering and small-angle neutron scattering.

In this study, the phase behavior, structure and properties of systems composed of the cationic, cellulose-based polycation JR 400 and the anionic surfactants sodium dodecylbenzenesulfonate (SDBS) or sodium dodecylethoxysulfate (SDES), mainly in the semidilute regime, were examined. This system shows the interesting feature of a very large viscosity increase by nearly 4 orders of magnitude as compared to the pure polymer solution already at very low concentrations of 1 wt%. By using rheology, dynamic light scattering (DLS), and small-angle neutron scattering (SANS), we are able to deduce systematic correlations between the molecular composition of the systems (characterized by the charge ratio Z=[+(polymer)]/[−(surfactant)]), their structural organization and the resulting macroscopic flow behavior. Mixtures in the semidilute regime with an excess of polycation charge form highly viscous network structures containing rodlike aggregates composed of surfactant and polyelectrolyte that are interconnected by the long JR 400 chains. Viscosity and storage modulus follow scaling laws as a function of surfactant concentration (η~c(s)(4); G(0)~c(s)(1.5)) and the very pronounced viscosity increase mainly arises from the strongly enhanced structural relaxation time of the systems. In contrast, mixtures with excess surfactant charges form solutions with viscosities even below those of the pure polymer solution. The combination of SANS, DLS, and rheology shows that the structural, dynamical, and rheological properties of these oppositely charged polyelectrolyte/surfactant systems can be controlled in a systematic fashion by appropriately choosing the systems composition.