Physical and interfacial characterization of phytosterols in oil-in-water triacylglycerol-based emulsions

peer-reviewedPhytosterols possess the ability to significantly lower low-density lipoprotein (LDL) cholesterol levels in the blood, but their bioaccessibility is highly dependent upon the solubility of the phytosterol within the carrier matrix. Currently, there is a limited amount of knowledge on how phytosterols interact at oil-water interfaces, despite research indicating that these interfaces could promote the crystallization of phytosterols and thus decrease bioaccessibility. In order to fill this knowledge gap, this work expands upon a previously studied emulsion system for encapsulating phytosterols and addresses whether phytosterols can crystalize at an oil-in-water emulsion interface. Images from multiple microscopic techniques suggest interfacial phytosterol crystallization in 0.6% phytosterol-enriched emulsions, while interfacial tension results and calculated models showed that whey protein and phytosterols had a synergistic effect on interfacial tension. A deeper understanding of the interfacial behavior of phytosterols in emulsions can provide the functional food and pharmaceutical industry with the knowledge needed to design more bioaccessible phytosterol-enriched products

Determining how polymer-bubble interactions impact algal separation using the novel "Posi"-dissolved air flotation process

The novel dissolved air flotation (DAF) process that uses hydrophobically-modified polymers (HMPs) to generate positively charged bubbles (PosiDAF) has been shown to separate negatively charged algal cells without the need for coagulation-flocculation. Previous research has been limited to HMPs of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and, while they were effective at bench-scale, performance at pilot-scale was better using commercial poly(N,N-diallyl-N,N-dimethylammonium chloride) (PDADMAC). Hence, the aim of this research was to compare the effectiveness of PDADMAC modified with aliphatic and aromatic moieties in comparison to previously tested PDMAEMA HMPs in respect to algal cell separation and minimisation of effluent polymer concentration, as well as defining the underlying polymer-bubble interaction mechanisms. Polymer-bubble adhesion properties were measured using atomic force microscopy (AFM) while polymer concentration was monitored via zeta potential and, where possible, assays using fluorescence spectroscopy. Both PDADMAC functionalised with a fluorinated aromatic group (PDADMAC-BCF) and PDMAEMA modified with 1-bromodecane respectively, gave effective cell separation, while the treated effluent zeta potential values at maximum cell removal were lower than the other polymers trialled. The effluent polymer concentration when using PDADMAC-BCF was four times lower in comparison to another aromatically modified PDADMAC polymer. AFM studies indicated that, in contrast to the PDMAEMA-based polymers, the PDADMAC-based polymers did not adsorb closely to the bubble surface. The different polymer-bubble interactions indicate that separation mechanisms will also vary, potentially leading to differences in process effectiveness when explored at pilot scale

Oscillatory packing and depletion of polyelectrolyte molecules at an oxide water interface

Total internal reflection microscopy (TIRM) has been used to study the interactions between a 5 μm borosilicate glass sphere and a silica slide in the presence of a nonadsorbing polyelectrolyte, sodium (polystyrene sulfonate) (NaPSS). The effect of the polymer concentration, within the dilute solution regime, on the observed interactions was investigated. In all cases, the interactions displayed a short-range electrostatic repulsion followed immediately, at larger separations, by a decaying oscillatory interaction that is attributed to structuring of the polyelectrolyte in solution. The periodicity of the oscillations, as a function of concentration, indicates that at large surface separations the polymer chains are ordered as a nonintermixing, space-filling, latex. At polymer concentrations of between 200 and 1000 ppm, a transition to a system of ordered rods, parallel to the interface was seen for the final layer of polymer molecules

Intrinsic defects in 3D printed materials

<p>We discuss the impact of bulk structural defects on the coherence, phase and polarisation of light passing through transparent 3D printed materials fabricated using a variety of commercial print technologies.</p

Direct comparison of atomic force microscopic and total internal reflection microscopic measurements in the presence of nonadsorbing polyelectrolytes

We have investigated the structural and depletion forces between silica glass surfaces in aqueous, salt-free solutions of sodium poly(styrene sulfonate). The interaction forces were investigated by two techniques: total internal reflectance microscopy (TIRM) and colloid probe atomic force microscopy (AFM). The TIRM technique measures the potential energy of interaction directly, while the AFM is a force balance. Comparison between the data sets was used to independently calibrate the AFM data since the separation distances cannot be unequivocally determined by this technique. Oscillatory structural forces are excellent for this work since they give multiple reference points against which to analyze. Comparison of the data from the two techniques highlighted significant uncertainties in the AFM data. At low polymer concentrations, a significant uncertainty in the apparent zero separation distance was seen as a result of the AFM cantilever reaching an apparent constant compliance region prior to any real contact between the surfaces. Further complications arising from the number and position of the measured minima were also seen in the dilute polymer concentration regime as a result of hydrodynamic drainage between the approaching surfaces in the AFM perturbing the delicate structural components in the fluid

The hydrophobic force: measurements and methods

The hydrophobic force describes the attraction between water-hating molecules (and surfaces) that draws them together, causing aggregation, phase separation, protein folding and many other inherent physical phenomena. Attempts have been made to isolate the range and magnitude of this interaction between extended surfaces for more than four decades, with wildly varying results. In this perspective, we critically analyse the application of common force-measuring techniques to the hydrophobic force conundrum. In doing so, we highlight possible interferences to these measurements and provide physical rationalisation where possible. By analysing the most recent measurements, new approaches to establishing the form of this force become apparent, and we suggest potential future directions to further refine our understanding of this vital, physical force

Microstructure and Composition of Full Fat Cheddar Cheese Made with Ultrafiltered Milk Retentate

Milk protein is often standardised prior to cheese-making using low concentration factor ultrafiltration retentate (LCUFR) but the effect of LCUFR addition on the microstructure of full fat gel, curd and Cheddar cheese is not known. In this work, Cheddar cheeses were made from cheese-milk with or without LCUFR addition using a protein concentration of 3.7%–5.8% w/w. The fat lost to sweet whey was higher in cheese made from cheese-milk without LCUFR or from cheese-milk with 5.8% w/w protein. At 5.8% w/w protein concentration, the porosity of the gel increased significantly and the fat globules within the gel and curd tended to pool together, which possibly contributed to the higher fat loss in the sweet whey. The microstructure of cheese from cheese-milk with a higher protein concentration was more compact, consistent with the increased hardness, although the cohesiveness was lower. These results highlight the potential use of LCUFR for the standardization of protein concentration in cheese-milk to 4%–5% w/w (equivalent to a casein to total protein ratio of 77%–79% w/w) to increase yield. Beyond this concentration, significant changes in the gel microstructure, cheese texture and fat loss were observed