Drying colloidal systems: laboratory models for a wide range of applications

The drying of complex fluids provides a powerful insight into phenomena that take place on time and length scales not normally accessible. An important feature of complex fluids, colloidal dispersions and polymer solutions is their high sensitivity to weak external actions. Thus, the drying of complex fluids involves a large number of physical and chemical processes. The scope of this review is the capacity to tune such systems to reproduce and explore specific properties in a physics laboratory. A wide variety of systems are presented, ranging from functional coatings, food science, cosmetology, medical diagnostics and forensics to geophysics and art

Equation of state and structure of highly concentrated globular protein solutions

In food technology, proteins are classically subject to operations leading to high local concentrations (membrane filtration, drying, stabilization of dispersed systems through the formation of dense interfacial films). However, few studies have for now been conducted on the behaviour of globular proteins in “highly crowded” situations, despite interesting observations in some cases and a growing interest in the subject [1,2]. Our goal is to study the crowding of proteins in an extended concentrIn food technology, proteins are classically subject to operations leading to high local concentrations (membrane filtration, drying, stabilization of dispersed systems through the formation of dense interfacial films). However, few studies have for now been conducted on the behaviour of globular proteins in “highly crowded” situations, despite interesting observations in some cases and a growing interest in the subject [1,2]. Our goal is to study the crowding of proteins in an extended concentration range, up to volume fractions about 0.5, using highly concentrated solutions obtained via the osmotic stress method [3]. Recently, this method has been used to study the behaviour of milk casein micelles upon concentration [4]. Equations of state, which relate concentration and osmotic pressure, were established for two well-known globular proteins, lysozyme and ovalbumin, in different charge and ionic strength conditions. We then conducted a SAXS study of the structure of the highly concentrated lysozyme and ovalbumin samples. We showed that the structure of the samples, depending on the protein, the charge and the range of interactions, underwent drastic structural changes and phase transitions upon concentration. In this communication, we will discuss the equations of state obtained for lysozyme and ovalbumin, then the structural properties of crowded lysozyme and ovalbumin as determined by SAXS studies, in the light of the molecular structure and physico-chemical properties of these two proteins, as well as the general behaviour and interaction properties of proteins

Osmotic pressures of lysozyme solutions from gas-like to crystal states

International audienceWe obtained osmotic pressure data of lysozyme solutions, describing their physical states over a wide concentration range, using osmotic stress for pressures between 0.05 bar and about 40 bar and volume fractions between 0.01 and 0.61. The osmotic pressure vs. volume fraction data consist of a dilute, gas-phase regime, a transition regime with a high-compressibility plateau, and a concentrated regime where the system is nearly incompressible. The first two regimes are shifted towards a higher protein volume fraction upon decreasing the strength or the range of electrostatic interactions. We describe this shift and the overall shape of the experimental data in these two regimes through a model accounting for a steric repulsion, a short-range van der Waals attraction and a screened electrostatic repulsion. The transition is caused by crystallization, as shown by small-angle X-ray scattering. We verified that our data points correspond to thermodynamic equilibria, and thus that they consist of the reference experimental counterpart of a thermodynamic equation of state. © the Owner Societies 2016

Structural markers of the evolution of whey protein isolate powder during aging and effects on foaming properties

The market for dairy powders, including high addedvalue products (e.g., infant formulas, protein isolates)has increased continuously over the past decade. However, the processing and storage of whey proteinisolate (WPI) powders can result in changes in their structural and functional properties. It is therefore ofgreat importance to understand the mechanisms and to identify the structural markers involved in the agingof WPI powders to control their end use properties. This study was performed to determine the effects ofdifferent storage conditions on protein lactosylations, protein denaturation in WPI, and in parallel on theirfoaming and interfacial properties. Six storage conditions involving different temperatures (θ) and wateractivities (aw) were studied for periods of up to 12 mo.The results showed that for θ ≤ 20°C, foaming propertiesof powders did not significantly differ from nonaged whey protein isolates (reference), regardless of the aw.On the other hand, powders presented significant levels of denaturation/aggregation and protein modificationinvolving first protein lactosylation and then degradation of Maillard reaction products, resulting in a higherbrowning index compared with the reference, starting from the early stage of storage at 60°C. These changesresulted in a higher foam density and a slightly better foam stability (whisking) at 6 mo. At 40°C, powdersshowed transitional evolution. The findings of this study will make it possible to define maximum storage durationsand to recommend optimal storage conditions in accordance with WPI powder end-use properties