Search Results (402)

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

In this work, alginate-chitosan microgel particles were formed at different pH levels with the aim of using them as viscoelastic interfacial layers, which confer emulsion stability to food systems. The particles’ size and structural characteristics were determined using laser diffraction, confocal laser microscopy (CLSM), and time-domain nuclear magnetic resonance (TD-NMR). The pH affected the microgel characteristics, with larger particles formed at lower pH levels. T₂ relaxation measurements with TD-NMR did not reveal differences in the mobility within the particles for the different pH levels, which could have been related to the more or less swollen structure. The rate of adsorption of the particles at the sunflower oil–water interface differed between particles formed at different pH levels, but the equilibrium interfacial tension of all systems was similar. Higher interfacial dilatational viscoelasticity was obtained for the systems at lower pH (3, 4, 5), with G’ reaching 13.6 mN/m (0.1 Hz) at pH 3. The interfacial rheological regime transitioned from a linear elastic regime at lower pH to a linear but more viscoelastic one at higher pH. The thicker, highly elastic interfacial layer at low pH, in combination with the higher charges expected at lower pH, was related to its performance during emulsification and the performance of the emulsion during storage. As revealed by laser diffraction and CLSM, the droplet sizes of emulsions formed at pH 6 and 7 were significantly larger and increased in size during 1 week of storage. CLSM examination of the emulsions revealed bridging flocculation with the higher pH. Nevertheless, all emulsions formed with microgel systems presented macroscopic volumetric stability for periods exceeding 1 week at 25 °C. A potential application of the present systems could be in the formation of stable, low-fat dressings without the addition of any emulsifier, allowing, at the same time, the release of the bioactive compounds for which such particles are known. Full article

The root of the licorice plant (Glycyrrhiza glabra) is rich in natural surfactants, called saponins. The beneficial properties of this plant have led to different applications, including its use as a foaming agent. In this research, a theoretical model and its validity are discussed for the liquid drainage of foams made from licorice root extract solutions. After stating the important characteristics in the free drainage of foam, a relationship of the drained liquid volume based on effective parameters was obtained via a simplification of the governing equation. The theoretical model is applied to experimental foam drainage data measured at different concentrations of licorice root extract solutions. A comparison of theoretical and experimental results shows good agreement for the volume of drained liquid as a function of time. The characteristics obtained from the combination of effective parameters allows for a quantification of the drainage rate. In addition, the drainage rate at the beginning of the foam decay process, as a measure of stability, can be estimated using measurable properties. Full article

Adsorption-based carbon dioxide capture, utilization, and storage technologies aim to mitigate the accumulation of anthropogenic greenhouse gases that cause climate change. It is assumed that porous carbons as adsorbents are able to demonstrate the effectiveness of these technologies over a wide range of temperatures and pressures. The present study aimed to investigate the temperature-induced changes in the dimensions of the microporous carbon adsorbent Sorbonorit 4, as well as the carbon dioxide adsorption, by using in situ dilatometry. The nonmonotonic changes in the dimensions of Sorbonorit 4 under vacuum were found with increasing temperature from 213 to 573 K. At T > 300 K, the thermal linear expansion coefficient of Sorbonorit 4 exceeded that of a graphite crystal, reaching 5 × 10⁻⁵ K at 573 K. The CO₂ adsorption onto Sorbonorit 4 gave rise to its contraction at low temperatures and pressures or to its expansion at high temperatures over the entire pressure range. An inversion of the temperature dependence of the adsorption-induced deformation (AID) of Sorbonorit-4 was observed. The AID of Sorbonorit-4 and differential isosteric heat of CO₂ adsorption plotted as a function of carbon dioxide uptake varied within the same intervals of adsorption values, reflecting the changes in the state of adsorbed molecules caused by contributions from adsorbate–adsorbent and adsorbate–adsorbate interactions. A simple model of nanoporous carbon adsorbents as randomly oriented nanocrystallites interconnected by a disordered carbon phase is proposed to represent the adsorption- and temperature-induced deformation of nanocrystallites with the macroscopic deformation of the adsorbent granules. Full article

A lot of applications for (semi-)crystalline triacylglycerol (TAG)-in-water dispersions exist in the life science and pharmaceutical industries. Unfortunately, during storage, these dispersions are often prone to changes in particle size due to unforeseen crystallization and recrystallization events. This results in the alterations of important product properties, such as viscosity and mouthfeel, or the premature release of encapsulated material. In this study, we investigated the effects and interplay of formulation, i.e., emulsifier combination, and processing parameters, i.e., cooling rate, on the colloidal stability of dispersed TAGs and aimed to improve their colloidal stability. We chose phospholipids (PLs) and β-lactoglobulin (β-lg) as the emulsifiers for our model systems, which are commonly applied in many food systems. When dispersions were characterized directly after cooling, we obtained smaller particles and narrower size distributions after fast cooling. Over the course of eleven weeks, the creaming behavior, particle size, melting behavior and polymorphism were characterized. The dispersions stabilized with solely β-lg exhibited a slight increase in particle size, whereas a decrease in size was found when PLs were added. Our results indicate that mass transport phenomena between TAG droplets and particles took place during storage. This migration of TAG molecules changed the composition and size distribution of the dispersed phase, especially at higher PL concentration (0.1 wt%). In our case, this could be prevented by using a lower concentration of PLs, i.e., 0.05 wt%. Full article

A novel electrophoretic separation technique is presented, where continuous electrophoretic separation is demonstrated using free flowing liquid foams. Continuous foam electrophoresis combines the principle of capillary electrophoresis and interactions between analytes and the electrical double layer, with the ability of Free Flow Electrophoresis to continuously separate and recover analytes automatically. A liquid foam is used to provide a network of deformable micro and nano channels with a high surface area, presenting a novel platform for electrophoresis, where interfacial phenomena could be exploited to modify analyte migration. The main purpose of this paper is to present a proof-of-concept study and provide fundamental understanding of a complex foam system in continuous separation mode, i.e., flowing liquid foam under an external electric field with electrophoresis and chemical reactions at the electrodes continuously changing the system. Liquid foam is generated using a mixture of anionic and non-ionic surfactants and pumped through a microfluidic separation chamber between two electrodes. The effectiveness of the device is demonstrated using a dye mixture containing a neutral dye and an anionic dye. At the outlet, the foam is separated and collected into five fractions which are individually probed for the concentration of the two dyes used. The anionic dye was concentrated up to 1.75 (±0.05) times the initial concentration in a select outlet, while the neutral dye concentration remained unchanged in all outlets, demonstrating the potential for electrophoretic foam separations. Full article

In heritage conservation, paper deterioration can be slowed down by controlling the environmental conditions surrounding heritage objects and stabilizing the materials these objects are made of. As conservation materials can also cause optical, chemical, and physical changes in the object, their application should be safe, minimalistic, and purposeful. This paper aimed to observe the functional applications of three biopolymers used in paper conservation. For that purpose, a model paper was coated with methylcellulose (MC), cellulose nanocrystals (CNCs), and wheat starch (WSP) using different wet film deposits. The prepared samples were characterized by determining their physical, optical, and surface properties. The results show that changes in the wet film deposit thickness influenced paper properties. With CNCs, the increase has caused a drastic change of colour properties, with MC hydrophobicity increased and with WSP grammage and thickness increased. All coatings (except CNC24) have contributed to the preservation of the colour properties of the paper from the damage caused by thermal ageing. Full article

The paper describes the use of native β-cyclodextrin (CD) for the modification of silver nanoparticles (AgNPs) in order to improve the determination of the anticancer drug methotrexate (MTX) using surface-enhanced Raman spectroscopy (SERS). A control experiment with unmodified AgNPs showed that the strong SERS signal of MTX can only be achieved in alkaline media. However, competitive interactions and the strong background signal of human body fluid components significantly challenge MTX determination in real samples. While previous reports propose the use of thorough sample pretreatment (e.g., solid phase extraction), the application of CD-modified AgNPs increases the SERS signal of MTX in neutral media by seven times which enables simplifying the analysis and improving its accuracy by reducing the influence of endogenous components of body fluids. A detailed study of the synthesis conditions (CD concentration and reaction time) and SERS registration conditions (pH, NaCl concentration, dilution of urine samples) was performed to maximize the analytical signal and signal-to-noise ratio. The final assay was tested for MTX determination in artificially spiked samples of real human urine. The results demonstrated that MTX can be determined within the concentration range suitable for therapeutic drug monitoring (20–300 μg mL⁻¹) with satisfactory precision (6–15% RSD), accuracy (95–111% apparent recovery), and limit of detection (0.3 μg mL⁻¹). Full article