Colloids Interfaces, Volume 7, Issue 3 (September 2023) – 12 articles

This study investigated the effect of the combined use of sodium caseinate (CAS), commercial phosphatidylcholine (PC), and modified PCs on the physical and oxidative stability of 70% fish oil-in-water emulsions. Caffeic acid was covalently attached to both modified PCs (PCs originated from soy and eggs) in order to increase the antioxidant activity of PCs and investigate the advantage of bringing the antioxidant activity to the close proximity of the oil-water interface. Results showed that oxidative stability was improved when part of the PC was substituted with modified soy PC or egg PC. Emulsions containing a low concentration of modified PCs (10 wt.% of total PC) resulted in a prooxidative effect on the formation of hydroperoxides compared to emulsions with free caffeic acid. On the other hand, a decrease in the formation of volatile oxidation products was observed for emulsions containing higher levels of modified PCs (60 wt.% of total PC) compared to the emulsions with free caffeic acid added at its equivalent concentration. Increased concentrations of modified PCs provided better oxidative stability in high-fat emulsions, independent of the modified PC type. Moreover, when oxidation was initiated by producing singlet oxygen near a single oil droplet using a focused laser, fluorescence imaging showed that the oxidation did not propagate from one oil droplet to another oil droplet. Full article

The surface properties of aqueous dispersions of worm-like fibril aggregates of bovine serum albumin (BSA) differ from those of the adsorption layers of the native protein. The dispersions of BSA fibrils are characterized by slower changes of the surface tension and dynamic surface elasticity and also have different steady-state values of the surface properties. The fourfold compression of the adsorption layer of BSA fibrils leads to noticeably higher surface pressures than those of a compressed layer of the native protein, indicating the formation of a more rigid layer structure in the former case. The spreading of BSA fibrils onto a liquid surface from a concentrated dispersion reduces the effect of surface-active admixtures on the layer properties. The dependencies of the dynamic surface elasticity on surface pressure almost coincide for the spread layers of fibrils and the native protein in the range of low surface pressures, but only the spreading of the native protein can lead to surface pressures higher than 4 mN/m. This distinction is presumably caused by the formation of stable clusters of BSA fibrils at the interface and their slow propagation along the liquid surface. Full article

The details of $ac$-conductivity measurements in a colloidal electrolyte cell with flat control gate electrodes are discussed. The use of impedance diagnostics in studies of transport phenomena in such systems requires caution in the definition of the thickness of the screening accumulation layers that appear along the metal-electrolyte interfaces. The value of this characteristic length ${\lambda }_0$ critically depends on the volume fraction ${\varphi }_{\odot }$ of colloidal particles in the bulk of the electrolyte. Accounting for the dependence ${\lambda }_0\left({\varphi }_{\odot }\right)$ makes it possible to consistently explain the large discrepancy in the available experimental data regarding the influence of the colloidal fraction on the effective conductivity of the colloidal suspension. Full article

This paper deals with the potential of aggregates of surfactant and SiO₂ nanoparticles as foam stabilizers for practical applications. The effects of different chain lengths and concentrations of the cationic surfactant ${\mathrm{C}}_n$TAB on the performance of ${\mathrm{C}}_n$TAB–SiO₂ nanofluids are examined to gain a comprehensive understanding of their ability to stabilize foam. The results indicate enhanced foam stability in the presence of SiO₂ nanoparticles. These findings help to better understand foam stabilization and its potential in various industrial applications such as enhanced oil recovery and foam-based separation processes. Full article

Interfacial compositions of fat globules modulate the digestion behaviour of milk triglycerides in the gastrointestinal tract, thereby affecting lipid metabolism and delivery of nutrients. In this study, we aim to understand the impact of emulsifiers on lipid digestibility and the self-assembled liquid crystal structures formed by anhydrous milk fat (AMF) during digestion. AMF was emulsified with casein and milk phospholipids, and digestion was performed in both gastric and small intestinal conditions to account for changes at the oil/water interface following enzymatic digestion in the gastric phase. Small angle X-ray scattering was used to characterise the self-assembled structures of the digestion products, while coherent anti-Stokes Raman scattering microscopy was utilised to probe changes in lipid distribution at the single droplet level during digestion. Our findings confirmed that emulsifiers play a key role in the digestion of AMF. Milk phospholipids exhibited a protective effect on milk triglycerides against pancreatic lipase digestion by slowing digestion, but this effect was slightly negated in emulsions pre-digested under gastric conditions. The overall types of liquid crystal structures formed after digestion of casein- and milk phospholipids-emulsified AMF were comparable to commercial bovine milk irrespective of gastric pre-treatment. However, emulsification of AMF with milk phospholipids resulted in changes in the microstructures of the liquid crystal phases, suggesting potential interactions between the digested products of the fat globules and milk phospholipids. This study highlights the importance of emulsifiers in regulating lipid digestion behaviour and lipid self-assembly during digestion. Full article

In many modern technologies, surface-active compounds, such as surfactants, polymers, proteins, particles and their mixtures, are essential components. They change the dynamic and equilibrium properties of the inherent interfaces, which is mostly visible in foams and emulsions. The interfacial dilational visco-elasticity is probably the most informative quantity due to its direct interrelation to the equation of state of the corresponding interfacial layers as well as the mechanisms governing the interfacial molecular dynamics. The scientific field of interfacial visco-elasticity, although quite young, has been inspired by the pioneering work of Marangoni, Levich, Lucassen, Lucassen-Reynders, Hansen, van den Tempel and Krotov, and during the last decades, also significantly by Boris Noskov. His contributions to the theoretical foundation and experimental analysis of polymer and mixed surfactant–polymer interfacial layers in particular are essential. Full article

Vacuum cold plasma (VCP), a novel non-thermal processing technology used to modify the physicochemical properties and functionalities of food materials, was applied to whey protein isolate (WPI). The treatment affects the protein chemistry and, as a result, leads to differences in the behavior in solution and at interfaces. To minimize the undesirable effects of high oxidation and to increase the effectiveness of reactive species, the VCP treatment was applied at low pressure using different types of gases (air, combination of argon and air, and sulfur hexafluoride (SF₆)). The treatment led to a decrease in the sulfur content and an increase in the carbonyl content, evidenced by oxidation reactions and enhanced disulfide bond formation, as well as cross-linking of protein molecules. Fluorescence-based indicators suggest that the hydrophobicity of the proteins as well as their aggregation increase after VCP treatment with an argon–air gas mixture; however, it decreases after VCP treatments with air and SF₆. The chemical modifications further lead to changes in the pH of aqueous WPI solutions, as well as the average size and ζ-potential of WPI aggregates. Moreover, the dynamic surface tension, surface dilational elasticity, and the thickness of the WPI adsorption layers at the air/water interface depend on the VCP type. SF₆ plasma treatment leads to a significant decrease in pH and an increase in the ζ-potential, and consequently to a significant increase in the aggregate size. The dynamic surface tension as well as the adsorption rates increase after SF₆VCP treatment, but decrease after air–VCP and argon–air–VCP treatments. The adsorbed WPI aggregates form strong viscoelastic interfacial layers, the thickness of which depends on the type of VCP treatment. Full article

This study presents a mathematical model of drop size distribution during dropwise condensation on a superhydrophobic surface. The model is developed by combining a power law growth model, an exponentially decaying population model, and a Gaussian probability model for growth variations. The model is validated against experiment data, with correlations ranging from 88% to 94%. The growth model is shown to sufficiently describe the growth of drops from 0.02 mm to 0.1 mm but may be extrapolated to describe the growth of even smaller drops. The experiment data show that drop size distribution or frequency distribution of drops of different sizes varies significantly with time and may be considered pseudo-cyclic. The developed model, together with the sweep rate of drops, sufficiently describes this behavior and, consequently, may also be used to better estimate the heat transfer rate due to dropwise condensation. Full article

The rheology of suspensions of solid particles in aqueous matrix liquids thickened by starch nanoparticles (SNP) was investigated. The SNP concentration varied from 9.89 to 34.60 wt% based on the aqueous matrix phase. The solids concentration of suspensions varied from 0 to 47 wt% (0 to 56 vol%). The suspensions at any given SNP concentration were generally Newtonian at low solids concentrations. At high solids concentrations, the suspensions were non-Newtonian shear-thinning. With the increase in the SNP concentration, the suspensions become non-Newtonian at a lower solids concentration. The rheological behavior of non-Newtonian suspensions could be described adequately with a power-law model. The consistency index of the suspension increased with the increase in solids concentration of the suspension at any given SNP concentration. The flow behavior index of suspensions was well below unity at high solids concentrations, indicating non-Newtonian shear-thinning behavior. The value of the flow behavior index decreased with the increase in solids concentration indicating an enhancement of shear-thinning in suspensions. The experimental viscosity and consistency data for Newtonian and non-Newtonian suspensions showed good agreement with the predictions of the Pal viscosity model for suspensions. Full article

The binding of drugs to nucleic acids, proteins, lipids, amino acids, and other biological receptors is necessary for the transportation of drugs. However, various side effects may also originate if the bound drug molecules are not dissociated from the carrier, especially with the aid of non-toxic agents. The sequestration of small drug molecules bound to biomolecules is thus central to counter issues related to drug overdose and drug detoxification. In this article, we aim to present several methods used for the dissociation of small drug molecules bound to different biological and biomimicking assemblies under in vitro experimental conditions. To this effect, the application of various molecular assemblies, like micelles, mixed micelles, molecular containers, like β-cyclodextrin, cucurbit[7]uril hydrate, etc., has been discussed. Herein, we also try to shed light on the driving forces underlying such sequestration processes through spectroscopic and calorimetric techniques. Full article

The optimization of fabrication conditions for colloidal micron-sized oblates obtained by the deformation of an oil-in-hydrogel emulsion is reported. The influence of the type of emulsion stabilizer, ultrasonication parameters, and emulsion and gel mixing conditions was explored. The best conditions with which to obtain more uniform particles were using polyvinyl alcohol as an emulsion stabilizer mixed with the gelatine solution at 35 °C and slowly cooling to room temperature. Four fractionation methods were applied to oblates to improve their size uniformity. The iterative differential centrifugation method produced the best size polydispersity reduction. Full article

Senior populations may experience nutritional deficiencies due to physiological changes that occur during aging, such as swallowing disorders, where easy-to-swallow foods are required to increase comfort during food consumption. In this context, the design of nanoemulsion-based gels (NBGs) can be an alternative for satisfying the textural requirements of seniors. This article aimed to develop NBGs with different gelling agents, evaluating their physical properties. NBGs were prepared with a base nanoemulsion (d = 188 nm) and carrageenan (CA) or agar (AG) at two concentrations (0.5–1.5% w/w). The color, rheology, texture, water-holding capacity (WHC) and FT-IR spectra were determined. The results showed that the CA-based gels were more yellow than the AG ones, with the highest hydrocolloid concentration. All gels showed a non-Newtonian flow behavior, where the gels’ consistency and shear-thinning behavior increased with the hydrocolloid concentration. Furthermore, elastic behavior predominated over viscous behavior in all the gels, being more pronounced in those with AG. Similarly, all the gels presented low values of textural parameters, indicating an adequate texture for seniors. The FT-IR spectra revealed non-covalent interactions between nanoemulsions and hydrocolloids, independent of their type and concentration. Finally, the CA-based gels presented a higher WHC than the AG ones. Therefore, NBG physical properties can be modulated according to gelling agent type in order to design foods adapted for seniors. Full article