Emulsions stabilised by whey protein microgel particles: Towards food-grade Pickering emulsions

We have investigated a new class of food-grade particles, whey protein microgels, as stabilisers of triglyceride-water emulsions. The sub-micron particles stabilized oil-in-water emulsions at all pH with and without salt. All emulsions creamed but exhibited exceptional resistance to coalescence. Clear correlations exist between the properties of the microgels in aqueous dispersion and the resulting emulsion characteristics. For conditions in which the particles were uncharged, fluid emulsions with relatively large drops were stabilised, whereas emulsions stabilized by charged particles contained smaller flocculated drops. A combination of optical microscopy of the drops and spectrophotometry of the resolved aqueous phase allowed us to estimate the interfacial adsorption densities of the particles using the phenomenon of limited coalescence. We deduce two classes of particle arrangement. Complete adsorption of the particles was obtained when they were neutral or when their charges were screened by salt resulting in at least one particle monolayer at the interface. By contrast, only around 50% of the particles adsorbed when they were charged with emulsion drops being covered by less than half a monolayer. These findings were supported by direct visualization of drop interfaces using cryo-scanning electron microscopy. Uncharged particles were highly aggregated and formed a continuous 2-D network at the interface. Otherwise particles organized as individual aggregates separated by particle-free regions. In this case, we suggest that some particles spread at the interface leading to the formation of a continuous protein membrane. Charged particles displayed the ability to bridge opposing interfaces of neighbouring drops to form dense particle disks protecting drops against coalescence; this is the main reason for the flocculation and stability of emulsions containing sparsely covered drops. © 2014 the Partner Organisations

Imaging subsurface damage of grinded fused silica optics by confocal fluorescence microscopy

International audienceWe report an experimental investigation of fluorescence confocal microscopy as a tool to measure subsurface damage on grinded fused silica optics. Confocal fluorescence microscopy was performed with an excitation at the wavelength of 405 nm on fixed abrasive diamond grinded fused silica samples. We detail the measured fluorescence spectrums and compare them to those of oil based coolants and grinding slurries. We evidence that oil based coolant used in diamond grinding induces a fluorescence that marks the subsurface damages and eases its observation. Such residual traces might also be involved in the laser damage process

A novel three-dimensional macrocellular carbonaceous biofuel cell

Here we report the first membrane-free biofuel cell obtained using three-dimensional carbonaceous foam electrodes. We first developed a new synthetic pathway to produce a new carbonaceous foam electrode material bearing porosity both on the meso and macroporous scales. We proved that by increasing the porosity of our three-dimensional foams we could increase the current density of our modified electrodes. Then, by choosing the right combination of enzyme and mediator, and the right loading of active components, we achieved high current densities for an anodic system. Finally, we combined the improved cathode and anode to build a new membrane-free hybrid enzymatic biofuel cell consisting of a mediated anode and a mediator-free cathode

Loose abrasive slurries for optical glass lapping

International audienceLoose abrasive lapping is widely used to prepare optical glass before its final polishing. We carried out a comparison of 20 different slurries from four different vendors. Slurry particle sizes and morphologies were measured. Fused silica samples were lapped with these different slurries on a single side polishing machine and characterized in terms of surface roughness and depth of subsurface damage (SSD). Effects of load, rotation speed, and slurry concentration during lapping on roughness, material removal rate, and SSD were investigated

Subsurface damage measurement of ground fused silica parts by HF etching techniques

International audienceDetection and measurement of subsurface damage of ground optical surfaces are of major concern in the assessment of high damage thresholds fused silica optics for high power laser applications. We herein detail a new principle of SSD measurement based on the utilization of HF acid etching. We also review and compare different subsurface damage (SSD) characterization techniques applied to ground and fine ground fused silica samples. We demonstrate good concordance between the different measurements

Pickering emulsions stabilized by coloured organic pigment particles

The possibility of stabilizing emulsions of water and non-polar alkane with pure, coloured organic pigment particles is explored. Seven pigment types each possessing a primary colour of the rainbow were selected. Their solubility in water or heptane was determined using a spectrophotometric method and their surface energies were derived from the contact angles of probe liquids on compressed disks of the particles. As expected, most of the pigments are relatively hydrophobic but pigment orange is quite hydrophilic. At equal volumes of oil and water, preferred emulsions were water-in-oil (w/o) for six pigment types and oil-in-water (o/w) for pigment orange. The emulsion type is in line with calculated contact angles of the particles at the oil–water interface being either side of 90°. Their stability to coalescence increases with particle concentration. Emulsions are shown to undergo limited coalescence from which the coverage of drop interfaces by particles has been determined. In a few cases, close-packed primary particles are visible around emulsion droplets. At constant particle concentration, the influence of the volume fraction of water (ϕw) on emulsions was also studied. For the most hydrophilic pigment orange, emulsions are o/w at all ϕw, whereas they are w/o for the most hydrophobic pigments (red, yellow, green and blue). For pigments of intermediate hydrophobicity however (indigo and violet), catastrophic phase inversion becomes possible with emulsions inverting from w/o to o/w upon increasing ϕw. For the first time, we link the pigment surface energy to the propensity of emulsions to phase invert transitionally or catastrophically.

High Performance Ultrasonic Inspection of Tubes

Eddy current examination was selected as the industrial method to be used for the inspection of PWR steam generator tubes because of both physical and operational advantages

Soybean protein isolate gel particles as foaming and emulsifying agents

In order to enhance functional properties of commercial soybean protein isolate (SPI), SPI microgel particles as foaming and emulsifying agents were studied. Microparticulation of heat-set SPI macrogels containing no added and various added salts was systematically carried out using a high-speed blender, an ultrasonicator and a high-pressure jet homogenizer. Among the tested conditions, the smallest gel particles were achieved via the high-pressure jet homogenization process under conditions of no added salts. Conversion of ordinary high molecular weight commercial SPI into the counterpart gel particles enhanced foam stabilizing properties of the suspensions and stability against creaming and freeze-thaw triggered instability of the emulsions, while the enhancement was not necessarily achieved for low-molecular-weight partially hydrolysed SPI. This can be attributed to the different steric repulsive effects of the gel particles

In vitro digestion of Pickering emulsions stabilized by soft whey protein microgel particles: influence of thermal treatment

Emulsions stabilized by soft whey protein microgel particles have gained research interest due to their combined advantages of biocompatibility and a high degree of resistance to coalescence. We designed Pickering oil-in-water emulsions using whey protein microgels by a facile route of heat-set gel formation followed by mechanical shear and studied the influence of heat treatment on emulsions stabilized by these particles. The aim of this study was to compare the barrier properties of the microgel particles and heat-treated fused microgel particles at the oil–water interface in delaying the digestion of the emulsified lipids using an in vitro digestion model. A combination of transmission electron microscopy and surface coverage measurements revealed an increased coverage of heat-treated microgel particles at the interface. The heat-induced microgel particle aggregation and, therefore, a fused network at the oil–water interface were more beneficial to delay the rate of digestion in the presence of pure lipase and bile salts compared to intact whey protein microgel particles, as shown by the measurements of zeta potential and free fatty acid release, plus theoretical calculations. However, simulated gastric digestion with pepsin impacted significantly on such barrier effects, due to the proteolysis of the particle network at the interface irrespective of the heat treatment, as visualized using sodium dodecyl sulfate polyacryl amide gel electrophoresis measurements

Whey protein microgel particles as stabilizers of waxy corn starch + locust bean gum water-in-water emulsions

Food-grade whey protein isolate (WPI) microgel particles were investigated as a particle stabilizer of water-in-water (W/W) emulsions. The microgel particles were produced via the novel method of forcing coarse particles of a pre-formed thermally processed WPI protein gel through a jet homogenizer. The Z-average particle size was 149 ± 89 nm but the particles showed a strong tendency for aggregation when the pH was lowered from pH 7 to 4, when the zeta potential also switched from -17 to +12 mV. The viscoelasticity of suspensions of the particles, measured between 1 and 15 vol.% (0.02 and 3 wt.%) increased with concentration and was also higher at pH 4 than pH 7. However, all the suspensions were only weakly shear thinning, suggesting that they did not form very strong networks. The particles were added (at 1-15 vol.%) to a model W/W system consisting of waxy corn starch (S) + locust bean gum (LBG) that normally shows phase separation when the components are mixed at 90 °C then cooled to room temperature (22-25 °C). At 10 to 15 vol.% particles and pH 4, visual observation showed striking inhibition of phase separation, for a period of up to 1 year. Confocal laser scanning microscopy suggested that under these conditions extensive aggregation of the microparticles occurred within the starch phase but also possibly at the W/W interface between the starch-rich and gum-rich regions, supporting a Pickering-type mechanism as responsible for the enhanced stabilization of the W/W emulsion by the microgel particles