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[Display omitted] In this paper, microgels with uniform particle size were prepared by physically cross-linking the hydrophobically modified chitosan (h -CS) with sodium phytate (SP). The effects of cross-linking density on the interfacial adsorption kinetics, viscoelasticity, stress relaxation, and micorheological properties of the hydrophobically modified chitosan microgels (h -CSMs) at the oil–water interface were extensively investigated by the dilatational rheology, compressional rheology, and particle tracing microrheology. The results were correlated with the particle size, morphology, and elasticity of the microgels characterized by dynamic light scattering and atomic force microscopy. It was found that with the increase of cross-linking density, the h -CSMs changed from a polymer-like state to ultra-soft fussy spheres with higher elastic modulus. The compression isotherms demonstrated multi-stage increase caused by the interaction between the shells and that between the cores of the microgels successively. As the increase of cross-linking density, the h -CSMs diffused slower to the oil–water interface, but demonstrating faster permeation adsorption and rearrangement at the oil–water interface, finally forming interfacial layers of higher viscoelastic modulus due to the core-core interaction. Both the initial tension relaxation and the microgel rearrangement after interface expansion became faster as the microgel elasticity increased. The interfacial microrheology demonstrated dynamic caging effect caused by neighboring microgels. This article provides a more comprehensive understanding of the behaviors of polysaccharide microgels at the oil-water interface. [ABSTRACT FROM AUTHOR]

How acute respiratory distress syndrome progresses from underlying disease or trauma is poorly understood, and there are no generally accepted treatments resulting in a 40% mortality rate. However, during the inflammation that accompanies this disease, the phospholipase A2 concentration increases in the alveolar fluids leading to the hydrolysis of bacterial, viral, and lung surfactant phospholipids into soluble lysolipids. We show that if the lysolipid concentration in the subphase reaches or exceeds its critical micelle concentration, the surface tension, γ, of dipalmitoyl phosphatidylcholine (DPPC) or Curosurf monolayers increases and the dilatational modulus, E*(w), decreases to that of a pure lysolipid interface. This is consistent with DPPC being solubilized in lysolipid micelles and being replaced by lysolipid at the interface. These changes lead to 2E* −γ < 0, which is the criterion for the Laplace instability that can lead to mechanical instabilities during lung inflation, potentially causing alveolar collapse. These findings provide a mechanism behind the alveolar collapse and uneven lung inflation during ARDS. [ABSTRACT FROM AUTHOR]

Hypothesis: Particle-laden interfaces play a crucial role in engineering stability of multiphase systems. However, a full understanding of the mechanical properties in shear and compression, especially in relation to the underlying microstructural changes, is as yet lacking. In this study, we investigate the interfacial rheological moduli in heterogeneous networks of aggregated 2D suspensions using different deformation modes and relate these moduli to changes in the microstructure. Experiments: Interfacial rheological experiments were conducted at different surface coverages and clean kinematic conditions, namely in (i) simple shear flow in a modified double wall-ring geometry and (ii) isotropic compression in a custom-built radial trough, while monitoring the evolution of the microstructure. Findings: The compressive moduli increase non-monotonically with decreasing void fraction, reflecting the combined effect of aggregate densification and reduction of void structures, with rotation of rigid clusters playing a significant role in closing voids. However, the shear moduli increase monotonically, which correlates with the increase in fractal dimension of the aggregates making up the backbone network. We also observe that these interfaces act as 2D auxetic materials at intermediate coverages, which is surprising given their amorphous structure. This finding has potential implications for the resilience of particle-coated bubbles or droplets subjected to time-varying compression-expansion deformations. • A flocculated interface was created as a model 2D system and compressed to different surface coverages. • This interface was studied using precise rheological measurements in simple shear and compression. • At low surface coverages, the elastic response is dominated by the compressional properties. • At higher coverages, shear properties dominate and a negative Poisson ratio arises. • This emerging auxetic behavior could be used as a strategy to design unique particle-laden interfaces. [ABSTRACT FROM AUTHOR]

Ethoxyamine derivatives of humic acids have been obtained by mechanochemical synthesis via the simultaneous interaction of humic acids with poly(ethylene glycol) (PEG-6000 and PEG-1500) and an aminating reagent (urea, hydroperitum, or cyanoguanidine) in a vibrating apparatus. Reaction products have been characterized by IR spectroscopy, acid–base potentiometric titration, and viscometry. Tensiometric and rheological characteristics of the surface layers of solutions of salts of the synthesized derivatives of humic acids have been studied by the pendant drop and oscillating pendant drop methods. The solutions of the salts of ethoxyaminohumic acids have been found to exhibit a pronounced surface activity at the air–water interface. The experimental dependences of the viscoelastic modulus on the surface pressure and the concentration of the solutions of ethoxyaminohumic acid salts are in satisfactory agreement with the functions calculated in terms of the theoretical model of bimolecular adsorption. The presence of amino groups in the structure of ethoxyaminohumic acids predetermines their high solubility in the acidic pH region. The simultaneous incorporation of ethoxy and amino groups into humic acid macromolecules makes it possible to obtain a novel type of surfactants, which combine three functions, i.e., the functions of anionic, cationic, and nonionic surfactants. [ABSTRACT FROM AUTHOR]

This study investigated the effects of pea protein pre-emulsions containing triglyceride- or diglyceride-oil on the emulsifying and gelling properties of low-salt myofibrillar protein (MP). Pea protein isolates treated with pH 12 -shifting (PPI pH) or ultrasonication (PPI U) demonstrated superior initial interfacial adsorption and higher final interfacial pressure than native pea protein. Within MP/PPI blends, an increased ratio of MP led to a decrease in interfacial pressure, while simultaneously enhancing film elasticity at both polar and non-polar interfaces. Polar diglyceride promoted protein adsorption and fostered interfacial interactions between modified pea proteins and MP, enhancing the cross-linking of transglutaminase (TG) in the composite emulsion gels. Combining diglyceride-type PPI U and PPI pH emulsions with TG increased gel strength to 0.58 N and 0.63 N, respectively, from an initial 0.33 N, yielding a denser protein network with uniformly dispersed oil droplets. Therefore, the utilization of diglyceride and modified PPI can serve as structural enhancers in comminuted meat products. [Display omitted] • Two modified pea protein isolates (PPIs) load faster at the oil-water interface. • The adsorbed PPI modified by ultrasound is easily replaced by myofibrillar protein. • The elasticity of mixed protein film is enhanced by the presence of diglyceride. • The role of transglutaminase becomes more prominent in gels containing diglyceride. • The microstructure of emulsion gel is observed by X-ray micro-computed tomography. [ABSTRACT FROM AUTHOR]

Simple BS/PC mixtures can substitute complex, real human bile in in vitro lipolysis. Findings improve design of in vitro models for studying lipid digestion. [Display omitted] • Bile salt/phosphatidylcholine mixtures can replicate human bile during lipolysis. • Bile salts alone are insufficient for mimicking interfacial behaviour of human bile. • Phospholipids can reduce desorption of interfacial material post-lipolysis. • Findings improve design of in vitro models for studying lipid digestion. This study examined the interfacial evolution of individual bile salts (BSs) and their blends with phosphatidylcholine (BS/PC) to simulate the complex behaviour of human bile (HB) during lipolysis at the triglyceride/water interface. Using adsorption and desorption cycles, mimicking exposure to small intestinal fluids, we demonstrate that the interfacial behaviour of real HB can be replicated using simple mixtures of BSs and PC. Interfacial tension (IFT) measurements after lipolysis and desorption showed no significant differences (P > 0.05) between HB samples and BS/PC mixtures across the total BS concentrations analysed (2.23–7.81 mM). However, individual BSs without PC yielded significantly different IFT results (P < 0.01) compared to HB, highlighting the importance of phospholipids. Dilatation rheology further emphasised the need for accurate phospholipid representation in bile models. Our results suggest that phospholipids in HB and in BS/PC systems enhance resistance to desorption, potentially affecting lipolysis. This is important, as current in vitro digestion models often replicate only intestinal BS concentrations to mimic the behaviour of HB in the intestinal lumen. Furthermore, the specific composition of BSs in HB appears less critical than the overall BS and phospholipid contents, suggesting that the kinetics of triglyceride digestion is influenced by the combined luminal concentrations of these components. These findings have significant implications for understanding the role of bile in digestion and offer insights for designing more accurate in vitro models to study the gastrointestinal behaviour of food emulsions and lipid-based delivery systems. [ABSTRACT FROM AUTHOR]

The physical stability of protein-based emulsions depends on intra- and intermolecular interactions of the interfacial protein-film. As studied in aqueous systems before, phenolic acid derivatives (PADs) non-covalently or covalently crosslink proteins depending on pH-value and thus, may impact interfacial protein-films. Whether these interactions occur in the same manner at the interface as in water and how they vary the properties of the interfacial protein-film has not been clarified. The present study aimed to investigate the interfacial protein-film viscoelasticity and physical emulsion-stability after non-covalently (pH 6.0) and covalently (pH 9.0) crosslinking depending on PAD-structure. For this purpose, we studied an interfacial β-lactoglobulin film with dilatational rheology after crosslinking with PADs, varying in number of π-electrons and polar substituents. Then, we analyzed the physical emulsion-stability by visual evaluation and particle size distribution. The results indicate that PADs with a high number of π-electrons (rosmarinic acid and chicoric acid) weaken the protein-film due to competing of phenol-protein interactions with protein-protein interactions. This is reflected in a decrease in interfacial elasticity. PADs with an additional polar substituent (verbascoside and cynarine) seem to further weaken the protein film, since the affinity of the PADs to the interface increases, PADs preferentially adsorb and sterically hinder protein-protein interactions. In emulsions at pH 6.0 and thus low electrostatic repulsion, PADs promote bridging-flocculation. Due to higher electrostatic repulsion at pH 9.0, the PADs are sterically hindered to form bridges, even though they are polymeric. Hence, our research enables the control of protein-film viscoelasticity and emulsion-stability depending on the PAD-structure. [ABSTRACT FROM AUTHOR]

A thin film of an amphiphilic block copolymer, poly(styrene)- b -poly(4-vinyl pyridine), is investigated at the air–water interface. The surface pressure - area per molecule isotherm and the static compressional modulus provide evidence of two phases, assigned as L 1 and L 2 , respectively. The surface topography and the phase images of these phases obtained using atomic force microscope reveal the presence of surface micelles of different sizes and densities. The dilatational rheology of these phases was investigated using the oscillatory barrier method for different strain amplitudes (1 − 5 %) and qualitatively assessed using Lissajous–Bowditch curves. It points out the emergence of nonlinearity (asymmetric shape and distorted ellipse) with an increase in strain amplitude. Using a fast Fourier transform, the amplitudes and the phases of different harmonics of the stress–strain curves were extracted, and the total harmonic distortion was determined. In contrast to L 1 phase, the total harmonic distortion for the L 2 phase increases monotonically with strain amplitude. Fixing the strain amplitude at 1% (small amplitude regime), the temperature as well as frequency dependence studies of the dilatational moduli were carried out. The dynamic storage moduli of the L 1 phase is found to be insensitive to temperature while it decreases for the L 2 phase suggesting softening. Further, evidence for solid-like viscoelastic response emerges (explained using the Kelvin–Voigt model) for the L 1 phase, whereas the L 2 phase show a cross-over behaviour. [Display omitted] • Langmuir films of the block copolymer, PS- b -P4VP show L 1 and L 2 phases. • Topography and phase images of PS- b -P4VP film show the presence of surface micelles. • Dilatational rheology studies on the BCP were carried out at the air–water interface. • Stress-strain responses were analysed using Lissajous–Bowditch curves and FFT. • L 1 (L 2) phase: Solid-like viscoelastic (non-linear, cross-over) behaviour. [ABSTRACT FROM AUTHOR]

This work investigates the influence of the enzymatic treatment (Alcalase or trypsin, degree of hydrolysis 5%) and pH (pH 7 or 4) on the interfacial and emulsifying properties of sunflower and olive protein hydrolysates. Independently of the enzymatic treatment, short peptides (1–3 kDa) were the most abundant in sunflower protein hydrolysates, whereas olive protein hydrolysates were richer in large peptides (>10 kDa). Peptides present in all hydrolysates gained in structure when adsorbing at the oil-water interface due to their facial amphiphilicity, with sunflower peptides presenting a more marked β-sheet conformation than olive peptides. Tryptic hydrolysates of both substrates showed higher interfacial adsorption compared to hydrolysates produced with Alcalase, especially at pH 4. All hydrolysates resulted in elastic interfaces, with generally higher values of dilatational complex modulus at pH 7 compared to pH 4. These findings correlated well with the higher emulsifying activity of all hydrolysates at pH 7 than pH 4. Particularly, sunflower protein hydrolysates led to stiffer and more solid-like viscoelastic interfacial layers than olive peptides due to increased interactions between β-sheet peptides at the interface. Indeed, the use of sunflower protein hydrolysates as emulsifiers resulted in 5 wt% oil-in-water emulsions with higher physical stability at both pH 7 and 4 when compared to olive protein hydrolysates. [Display omitted] • Sunflower (SF) and olive(O) hydrolysates were used to stabilize O/W emulsions. • Interfacial properties and secondary structure of peptides was studied at pH 4/7. • O and SF peptides gained β-sheet structure when adsorbed at the O/W interface. • O and SF tryptic hydrolysates showed better interfacial adsorption at pH 4. • SF showed better emulsifiying properties due to higher interfacial viscoelasticity. [ABSTRACT FROM AUTHOR]

Whey protein isolate (WPI) is an excellent emulsifier. However, WPI-stabilized emulsions tend to flocculate at pH values close to their isoelectric point. In this work, a layer by layer (LBL) technique was used to develop double layer oil in water emulsions using a mixture of WPI and water-soluble fraction of Persian gum (WSPG). Polysaccharide concentration and pH were found to have a major impact on the stability of the final system. At a constant total biopolymer concentration, increasing the amount of WSPG significantly (p < 0.05) improved the emulsion physical stability. An appropriate stability was obtained at 0.5 wt% WPI, 1 wt% WSPG, and pH 5.0. At high ionic strength, the emulsions became unstable with a higher sensitivity to CaCl2 than NaCl. Confocal laser scanning microscopy and zeta-potential measurements confirmed the electrostatic adsorption of WSPG onto the WPI-stabilized oil droplets. The results of interfacial tension and dilatational rheology measurements revealed a slight decrease in the interfacial tension after the adsorption of WSPG as the second layer and a predominantly elastic behavior (E′ > E″), at the interface especially at pH 5.0. The results showed that WSPG is an appropriate candidate for improving the physical stability of WPI-stabilized emulsions at pH values close to isoelectric point. [ABSTRACT FROM AUTHOR]

Oleanolic acid (OLA) and oleic acid (OA) are ubiquitous in the plant kingdom, exhibiting a therapeutic effect on human health, and are components of novel pharmaceutical formulations. Since OLA has limited solubility, the utilization of nanotechnology-based drug delivery systems enhancing bioavailability is highly advantageous. We report on the interfacial behavior of the OLA:OA system at various molar ratios, using the Langmuir technique to assess the dependence of the molar composition on miscibility and rheological properties affecting film stability. Specifically, we evaluate the interfacial properties (morphology, thermodynamics, miscibility, and viscoelasticity) of the OLA:OA binary system in various molar ratios, and indicate how the OLA:OA system exhibits the most favorable molecular interactions. We apply the Langmuir monolayer technique along with the complementary techniques of Brewster angle microscopy, dilatational interfacial rheology, and excess free energy calculations. Results demonstrate that the properties of mixed monolayers depend on OLA:OA molar ratio. Most of the systems (OLA:OA 2:1, 1:1, 1:5) are assumed to be immiscible at surface pressures >10 mN/m. Moreover, the OLA:OA 1:2 is immiscible over the entire surface pressure range. However, the existence of miscibility between molecules of OLA and OA in the 5:1 for every surface pressure tested suggests that OA molecules incorporate into the OLA lattice structure, improving the stability of the mixed film. The results are discussed in terms of providing physicochemical insights into the behavior of the OLA:OA systems at the interface, which is of high interest in pharmaceutical design.

[Display omitted] • BSs and PLs synergistically lower oil–water interfacial tension during lipolysis. • BSs and PLs contribute differently to oil–water interfacial viscoelasticity. • BSs desorb much easier from oil-water interface compared to PLs. • BS/PL–9:4 molar ratio was found optimal for effective intestinal lipolysis of TGs. • Presence/concentration of biliary PLs should be replicated in in vitro lipolysis. This study focused on the protein-stabilised triglyceride (TG)/water interfaces and oil-in-water emulsions, and explored the influence of varying molar ratios of bile salts (BSs) and phospholipids (PLs) on the intestinal lipolysis of TGs. The presence of these two major groups of biosurfactants delivered with human bile to the physiological environment of intestinal digestion was replicated in our experiments by using mixtures of individual BSs and PLs under in vitro small intestinal lipolysis conditions. Conducted initially, retrospective analysis of available scientific literature revealed that an average molar ratio of 9:4 for BSs to PLs (BS/PL) can be considered physiological in the postprandial adult human small intestine. Our experimental data showed that combining BSs and PLs synergistically enhanced interfacial activity, substantially reducing oil–water interfacial tension (IFT) during interfacial lipolysis experiments with pancreatic lipase, especially at the BS/PL–9:4 ratio. Other BS/PL molar proportions (BS/PL–6.5:6.5 and BS/PL–4:9) and an equimolar amount of BSs (BS–13) followed in IFT reduction efficiency, while using PLs alone as biosurfactants was the least efficient. In the following emulsion lipolysis experiments, BS/PL–9:4 outperformed other BS/PL mixtures in terms of enhancing the TG digestion extent. The degree of TG conversion and the desorption efficiency of interfacial material post-lipolysis correlated directly with the BS/PL ratio, decreasing as the PL proportion increased. In conclusion, this study highlights the crucial role of biliary PLs, alongside BSs, in replicating the physiological function of bile in intestinal lipolysis of emulsified TGs. Our results showed different contributions of PLs and BSs to lipolysis, strongly suggesting that any future in vitro studies aiming to simulate the human digestion conditions should take into account the impact of biliary PLs – not just BSs – to accurately mimic the physiological role of bile in intestinal lipolysis. This is particularly crucial given the fact that existing in vitro digestion protocols typically focus solely on applying specific concentrations and/or compositions of BSs to simulate the action of human bile during intestinal digestion, while overlooking the presence and concentration of biliary PLs under physiological gut conditions. [ABSTRACT FROM AUTHOR]

Proteins are able to stabilize dispersed food systems due to their amphiphilic nature, acting as emulsifiers. Their interfacial properties can be influenced by different methods, including the formation of protein-phenol nanocomplexes. In this study, the interfacial behavior of phenolic compounds and protein-phenol nanocomplexes was first characterized according to the oil-water partitioning behavior of phenolic acid derivatives according to their molecular structure and its impact on interfacial tension. The influence of the phenolic compounds on protein film formation and its properties by dilatational rheology was then evaluated. The most phenolic acid derivatives are predominantly present in the aqueous phase. Despite their hydrophobic benzene body, weak interfacial activity was observed depending on their chemical structure. This result supports possible protein-phenol nanocomplex formation in the aqueous phase and possible interactions at the oil-water interface. Protein-phenol nanocomplexes showed decreased interfacial adsorption properties and decreased viscoelastic interfacial behavior, depending on the expansion of the delocalized π-electrons in the phenol. [ABSTRACT FROM AUTHOR]

In spray dried emulsions, frequently milk proteins are used as interfacial active components and starch conversion products are added as matrix material at high concentrations. To characterize interfacial properties at the oil/water interface by commonly applied methods, low protein, and carbohydrate concentrations from 1 to 2% are usually analyzed. The impact of a higher concentration of starch conversion products was not investigated so far. Therefore, the formation and rheological properties of β-lactoglobulin (β-LG) stabilized films at the oil/water interface were investigated via short and long-time adsorption behavior using pendant drop tensiometry as well as dilatational and interfacial shear rheology. Suitability of the applied methods to the chosen samples with higher concentrations >1–2% was verified by calculation of selected key numbers like capillary number and by detailed reviewing of the results which is summarized further on as key indicators. It is hypothesized, that the increase in concentration via presence of starch conversion products will delay interfacial stabilization as a result of increased bulk viscosity with decreasing degree of degradation (dextrose equivalent) of the starch. Furthermore, this increase in concentration leads to more stable interfacial films due to thermodynamic incompatibility effects between protein and starch conversion products which results in increases of local protein concentration. Key indicators proved a general suitability of applied methods for the evaluation of the investigated samples. Moreover, results showed an increase in interfacial film stability and elastic properties alongside a decreased interfacial tension if starch conversion products were present in a high concentration. [ABSTRACT FROM AUTHOR]

The Chaplin E peptide is a surface-active agent that can adsorb to the air/water interface and form interfacial films that display distinct interfacial properties as a function of pH. The ~2 nm thick homogeneous Chaplin E film formed under acidic conditions contains ordered structures that give a high dilatational elasticity. In contrast, the heterogeneous film formed under basic conditions contained fibrils resulting in a rough ~17 nm thick film with predominantly viscoelastic properties, probably due to the reduced intermolecular interactions. These fibrils were also susceptible to breakage, fragmenting into shorter fibrils, which gave a greater elasticity. The fibrils also lead to a greater shear viscosity compared to the ordered structures aligned within the Chaplin E film at pH 3.0. A higher stability was observed for the foam formed by the Chaplin E compared to the foam formed by β-lactoglobulin, consistent with the greater rheological properties observed for the Chaplin E film at the interface. Our findings suggest that Chaplin E has potential to provide long time stability to dispersions in food, consumer goods or pharmaceutical applications, forming films with greater rheological properties and at least similar thickness to those formed by other surface-active proteins such as β-casein and β-lactoglobulin. • The Chaplin E films possess distinct interfacial properties as a function of pH. • The Chaplin E interfacial films have exceptional rheological properties. • The Chaplin E films are at least as thick as the model milk protein films. • The foam formed by the Chaplin E is more stable than β-lactoglobulin foam. • Chaplin E has potential to provide long time stability to dispersions. [ABSTRACT FROM AUTHOR]

The interplay between colloidal particles and surfactant co-adsorption plays a pivotal role in determining interface properties and emulsion stability. This study delves into the influence of the Zp/GMS ratio on the physical stability of Zein particle-GMS co-stabilized emulsions (CPEs) and how co-adsorption and interfacial interactions impact this stability. Results indicated that the preferential adsorption of GMS facilitated the diffusion (K diff increased from 0.083 mNm−1 s−0.5 to 0.206 mNm−1 s−0.5) and penetration of Zp (K P increased from −17.0 × 104 s−1 to −23.6 × 104 s−1), triggering interface rearrangement. Consequently, intricate interfaces formed, inducing a synergistic reduction in interfacial tension. Moreover, the decreased Zp/GMS ratio bolstered the lateral molecular interactions between Zp and GMS at the interface, while also enhancing the longitudinal relaxation of GMS during interface deformation. Therefore, the Zp/GMS ratio played a pivotal role in controlling the stiffness, elasticity, and deformability recovery of complex interfaces in both lateral and longitudinal dimensions. Furthermore, in both O/W and W/O CPEs, a decreased Zp/GMS ratio improved the physical stability of CPEs by reducing the rate of droplet coalescence. To summarize, the enhanced stability of CPEs can be attributed to the reduction in droplet aggregation. This reduction is influenced by a combination of improved mechanical properties resulting from lateral molecular interactions at the interface and enhanced deformability recovery due to the longitudinal relaxation of GMS. These findings not only deepen our understanding of particle-surfactant interactions in Pickering emulsions but also pave the way for formulating emulsions with specific textures and stabilities. [Display omitted] • Explored particle-surfactant interactions in Pickering emulsions. • Zp/GMS ratio modulates emulsion type and microstructure in CPEs. • GMS influences interface formation and synergistically reduces tension. • GMS results in a complex interface with enhanced elasticity and rigidity. • Co-adsorption of Zp and GMS improves thermodynamic stability by retarding droplet coalescence. [ABSTRACT FROM AUTHOR]

Drying of latex dispersions often results in particle gradients at the latex-air interface. We expect that, by increasing the carboxylic acid content of latex particles, inter-particle interactions at the interface change. With dilatational rheology one could detect particle-particle interactions in an early stage of the drying process and elucidate the nature of these interactions. Acrylic latex dispersions were prepared with different amounts of methacrylic acid (MAA), ranging from 2 to 10 wt% on dry mass. Dilatational rheology studies during drying at different relative humidities RH were performed using profile analysis tensiometry. Visco-elastic properties of latex surfaces were used to identify inter-particle interactions at the surfaces depending on the drying rate and particle composition. Drying at 85% RH did not show significant changes of the mechanical properties of the latex surfaces. Drying at 65 and 53% RH resulted in a change of the mechanical properties, ultimately showing non-linear visco-elastic behavior. This indicates that capillary and/or Van der Waals forces were operating between particles at the surface. With increasing MAA content the viscous contribution decreased, possibly due to the formation of more gel-like structures at the particle surface due to higher solubility of polymer segments near to the surface. [ABSTRACT FROM AUTHOR]

Interfacial and emulsifying properties of flaxseed protein isolate (FPI) and its phenolic complexes were studied, aiming to develop plant-based natural emulsifiers with improved interfacial and oxidative activity and adding value to the by-product of flaxseed oil production. Flaxseed polyphenols (FPP) and hydroxytyrosol (HT) were used as model phenolic compounds. The stability of emulsions produced using FPI, FPI-FPP and FPI-HT as emulsifiers was measured and correlated with their solubility and surface charge. The dynamic interfacial tension (DIT) and dilatational elasticity (E′) and viscosity (E") were measured at flaxseed oil/water interface. The diffusion and penetration rate constants were calculated using DIT data. The complexation of FPI with FPP and HT significantly increased the diffusion rate constant at low FPI concentration (0.1 mg mL−1). At higher FPI concentration (from 1 to 10 mg mL−1), the DIT and penetration rate constant of FPI, FPI-FPP and FPI-HT were not different. The E' of interfacial layer of FPI was lower than that of FPI-HT interfacial layer but was higher than that of FPI-FPP interfacial layer. The E" of FPI-FPP and FPI-HT complexes was lower than that of FPI. FPI-stabilised emulsion with higher charge density had higher physical stability compared to the emulsions stabilised by FPI-phenolic complexes which had lower charge density. The emulsions stabilised by FPI-FPP and FPI-HT complexes had higher antioxidative stability compared to that of FPI stabilised emulsion. The emulsions stabilised by FPI-FPP and FPI-HT complexes had higher red and yellow hue than the emulsion stabilised by FPI. Image 1 • Dilatational elasticity of FPI-phenolic complexes depended on the nature of phenolics. • Emulsion stability of FPI-HT complexes was lower than that of FPI. • Surface charge of emulsions contributed more to emulsion stability than their size. • FPI-phenolic complexes as emulsifiers accorded greater antioxidant property than FPI. • Emulsion stabilised by FPI-FPP and FPI-HT had higher red and yellow hue than by FPI. [ABSTRACT FROM AUTHOR]

Adsorption layers at the air-water interface formed from the soluble zwitterionic surfactant dodecylphosphorylcholine (DPC) serving as a soluble model substance for phospho-lipids were characterized with respect to their equilibrium and dynamic surface properties. To clarify the effect of ionic interactions with electrolyte present in the bulk phase, surface rheological properties upon addition of Ce(NO 3) 3 and Yb(NO 3) 3 were determined. In order to account for the surface activity of the nitrate ion, comparative measurements using NaNO 3 were carried out additionally. Further experimental information on the bulk hydration characteristics of the aqueous solutions was obtained using dielectric relaxation spectroscopy (DRS). A possible mechanism causing the deviating surface dilatational modulus E in terms of ion specificity is suggested. [ABSTRACT FROM AUTHOR]

In this study, the impact of pH-shift (PV-pH), controlled heating (PV–H), high intensity ultrasound (PV–U), and their combinations (PV-pH-H, PV-pH-U, PV-H-U) on the structural, foaming, and surface behavior at the air-water interface of the modified pea vicilin (PV) protein fraction were comprehensively evaluated. Results showed that the foaming capacity (FC) of samples treated by either PV-pH or PV-H was significantly increased (105.26%, 105.64%) as compared to the control (73.53%). This synergistic effect was observed with the combination of pH-shift and controlled heating (PV-pH-H), which drastically improved the FC of the modified PV (153.97%). Interestingly, ultrasound treatment exhibited the least effect on the FC of PV, no matter whether it was applied individually or combined with other treatments. The improved FC of PV was mainly attributed to newly formed soluble aggregates, the transition of β-sheet to α-helix, and increased surface hydrophobicity (H 0), allowing PV to exist in a more flexible structure. The dynamic adsorption behaviors of the modified PV at the air-water interface indicated that its improvement in FC was also associated with the high surface pressure with short lag time. In addition, the modified PVs formed a strong elastic interfacial film through densely packed protein molecule as evidenced by E-π slop (>1). This study demonstrated that a simple pH shift combined with controlled heating technique could be applied to improve the foaming properties of PV. [Display omitted] • Combined pH-shift and heating significantly increased the foaming capacity of PV. • Modifying PV led to the formation of soluble non-covalently linked protein aggregates. • Air-water interfacial films stabilized by modified PV had higher elastic moduli. • The modification improved PV's foaming capacity without compromising stability. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Interfacial and colloidal properties underlying synthesis of NPs by W/O/W technique. • Surfactant (F68) added from water improves colloidal and biological NP properties. • An in vitro model to mimic the first step of the W/O/W NP synthesis is developed • F68 added from water displaces more protein from interface protecting its structure. Abstract Hypothesis The use of polymer-based surfactants in the double-emulsion (water/oil/water, W/O/W) solvent-evaporation technique is becoming a widespread strategy for preparing biocompatible and biodegradable polymeric nanoparticles (NPs) loaded with biomolecules of interest in biomedicine, or biotechnology. This approach enhances the stability of the NPs, reduces their size and recognition by the mononuclear phagocytic system, and protects the encapsulated biomolecule against losing biological activity. Different protocols to add the surfactant during the synthesis lead to different NP colloidal properties and biological activity. Experiments We develop an in vitro model to mimic the first step of the W/O/W NP synthesis method, which enables us to analyze the surfactant-biomolecule interaction at the O/W interface. We compare the interfacial properties when the surfactant is added from the aqueous or the organic phase, and the effect of pH of the biomolecule solution. We work with a widely used biocompatible surfactant (Pluronic F68), and lysozyme, reported as a protein model. Findings The surfactant, when added from the water phase, displaces the protein from the interface, hence protecting the biomolecule. This could explain the improved colloidal stability of NPs, and the higher biological activity of the lysozyme released from nanoparticles found with the counterpart preparation. [ABSTRACT FROM AUTHOR]

Foaming ability of oat protein isolate (OPI) was analysed at pH 4 and 7. Foaming properties were influenced by partial hydrolysis with trypsin (OPT) and alcalase (OPA). The viscoelasticity of the protein film, the interactions between the protein molecules, and the network forming within the protein film were analysed by interfacial rheology. At pH 7, foams made of OPI and OPT were found to be stable with OPI showing the fastest foaming ability. At pH 4, the foaming properties of OPI were found to be poor due to limited solubility. The specific cleavage pattern of trypsin resulted in peptides with improved foaming properties, especially at pH 4, resulting in a homogenous foam structure, a fast foaming ability, and a highly viscoelastic interfacial film. The formation of a thick steric protein layer at pH 7 and the formation of strong hydrophobic interactions at pH 4 were found to be the dominating foam stabilisation mechanisms. In conclusion, oat protein may serve as a food ingredient with targeted functional properties. [ABSTRACT FROM AUTHOR]

Gliadins are edible wheat storage proteins well known for their surface active properties. In this paper, we present experimental results on the interfacial properties of acidic solutions of gliadin studied over 5 decades of concentrations, from 0.001 to 110 g/L. Dynamic pendant drop tensiometry reveals that the surface pressure Π of gliadin solutions builds up in a multistep process. The series of curves of the time evolution of Π collected at different bulk protein concentrations C can be merged onto a single master curve when Π is plotted as a function of α t where t is the time elapsed since the formation of the air/water interface and α is a shift parameter that varies with C as a power law with an exponent 2. The existence of such time-concentration superposition, which we evidence for the first time, indicates that the same mechanisms govern the surface tension evolution at all concentrations and are accelerated by an increase of the bulk concentration. The scaling of α with C is consistent with a kinetic of adsorption controlled by the diffusion of the proteins in the bulk. Moreover, we show that the proteins adsorption at the air/water interface is kinetically irreversible. Correlated evolutions of the optical and elastic properties of the interfaces, as probed by ellipsometry and surface dilatational rheology respectively, provide a consistent physical picture of the building up of the protein interfacial layer. A progressive coverage of the interface by the proteins occurs at low Π . This stage is followed, at higher Π , by conformational rearrangements of the protein film, which are identified by a strong increase of the dissipative viscoelastic properties of the film concomitantly with a peculiar evolution of its optical profile that we have rationalized. In the last stage, at even higher surface pressure, the adsorption is arrested; the optical profile is not modified while the elasticity of the interfacial layer dramatically increases with the surface pressure, presumably due to the film ageing. [ABSTRACT FROM AUTHOR]

The interfacial activity of commercial low-methoxy (LM) and high-methoxy (HM) pectins from citrus peel was investigated at air-water interfaces by focusing on the role of their molecular weight (MW) and degree of methoxylation (DM). A pendant drop tensiometer was used to carry out transient interfacial tension measurements and small amplitude oscillations. Different pectin concentrations (ranging between 0.00001 g/100 g and 5 g/100 g) and pH conditions (4 and 6) were used during the tests. It was observed that citrus pectins are characterised by interesting surface properties that could allow potential practical uses. Experimental results evidenced that MW affects the diffusion of molecules towards the interface, whereas other investigated parameters (i.e. surface tension, adsorption rate, dynamic moduli) seem more dependent on DM and a clear dependence on MW was not observed. pH conditions modify intermolecular interactions in the bulk and surface layer, even if their effects are related to the fraction and distribution of carboxylic groups along the chain. As a consequence, a complex dependence on investigated parameters was observed and no clear relationship was obtained. Nevertheless, among tested commercial samples LM pectins exhibited the most interesting properties and this behaviour seems related to the intermolecular interactions occurring among them. [ABSTRACT FROM AUTHOR]

AS-48 is a bacteriocin with potential application as food biopreservative. In order to optimize its use for oral consumption, we assess the impact of gastrointestinal digestion, both in bulk and adsorbed at the air-water interface. Analysis of AS-48 digestion fragments in bulk by SDS-PAGE, RP-HPLC, and MALDI-TOF proves that the previous pepsin exposition promotes digestion by trypsin/chymotrypsin by exposing new cleavage sites. Regarding adsorbed AS-48, the in vitro digestion profile shows that the conformational change undergone by AS-48 upon adsorption affects its digestibility. Gastrointestinal enzymes cleave only susceptible residues, which are oriented into the aqueous phase, while hydrophobic susceptible residues remain undigested. Evaluation of the elasticity of the adsorbed layer confirms also the presence of undigested AS-48. These results are important towards the use of AS-48 in food formulations; assuring that some intact AS-48 resists digestion guarantees its antibacterial activity throughout the gastrointestinal tract. [ABSTRACT FROM AUTHOR]

It is of fundamental importance for the petroleum industry to promote the coalescence of water droplets that may be dispersed in oil. Therefore, it is necessary to understand the rheological properties of the water/oil interface, which is straightly related to emulsion stability. This work aimed to present a practical approach about water/oil interface in realistic systems, i.e., using a crude oil and water or brine solution, the last one with the same composition of the water produced along with the oil production. Thus, it was investigated the water/crude oil and brine/crude oil interfaces in terms of their rheological properties at temperatures ranging from 30 °C to 60 °C. The interfacial rheological measurements were performed by the oscillatory pendant drop technique. The results indicated that temperature has a negligible effect on the interface properties; however, the salt content in the water phase resulted in an increase in the viscous modulus between 30 °C and 60 °C. The interfacial viscous and elastic moduli were shown to be dependent on the droplet oscillation period. Despite the elastic modulus being almost the same for water and brine, for the brine system the viscous modulus was significantly higher than that observed for water. [ABSTRACT FROM AUTHOR]

Self assembled β -lactoglobulin nanofibrils of different morphologies (long semi-flexible or short worm-like) were prepared at pH 2 and 85 °C in the aqueous solution containing different amount of ethanol. The effects of fibril morphology and polarity of the hydrophobic sub-phase on the interfacial adsorption kinetics, viscoelasticity, and structuration of the protein fibrils were investigated using dilatational rheology. It was found that the fibrils have three-stage adsorption at all the oil-water interfaces: diffusion-controlled adsorption in early stage, penetration adsorption near the interface and rearrangement within the interface. Diffusion adsorption rate (K dif) decreases while penetration rate (k ads) and rearrangement (k r) increase with increasing oil polarity. The strength and structuration of the interfacical fibril networks decrease with increasing oil polarity. The forces maintaining the stability of the protein fibril interface were mainly hydrophobic interaction. K dif , k ads and k r of the short fibrils are higher than those of the long fibrils due to their smaller size and higher surface hydrophobicity. The long fibril interface displayed strain softening response during both extension and compression, but form stronger interface than short fibrils, and thus demonstrate better foaming and emulsification ability. The short worm-like fibril interface displays strain softening during extension but strain hardening during compression, which is to some degree similar to the behavior of native flexible protein molecules. [Display omitted] • Oil polarity and fibril morphology influence interfacial structure and rheology of fibrils. • Diffusion decreases while penetration and rearrangement increase with increasing oil polarity. • Strength and structuration of fibril interface decrease with increasing oil polarity. • Short fibrils have faster adsorption kenetics but weaker interface strength that long fibrils. [ABSTRACT FROM AUTHOR]

• Acacia gum preferentially adsorbs to oil interfaces with low oil–water interaction energy. • Enhanced Acacia gum adsorption induces high oil surface coverage, interfacial layer elasticity and reduction of interfacial tension. • Density fluctuations near hydrophobic interfaces and hydrophobic effect lead Acacia gum to form a dehydrated structured interphase. • A volumetric Acacia gum adsorption mechanism based on oil–water interaction energy is proposed. Adsorption from Acacia gum of hyperbranched arabinogalactan-proteins (AGPs) to oil–water interfaces has been extensively studied and is known to contribute to colloidal stabilization of emulsions. Interfacial tension and rheological analyses revealed AGPs form a viscoelastic interfacial structure through a 3-phase mechanism. Yet, the role of water is generally not considered, even though it is the major and the most dynamic component of the oil-gum-water structure. This article aimed to explore the importance of oil–water interactions on the ability of hydrated Acacia gum to form a dehydrated structured oil-gum-water interphase. Interfacial tension and dilatational rheological measurements were performed using oils differing in hydrophobicity. While the hydrophilic characteristics of AGPs are largely predominant due to their polysaccharide content, their adsorption mechanism is similar to that of proteins, i.e. it is favored near highly hydrophobic interfaces. A volumetric Acacia gum adsorption mechanism is proposed based on the assumptions i) favored interaction energy between water and oil, in particular OH-containing oils involving hydrogen-bond, limits the AGPs interfacial properties, and ii) the surface pressure is a direct measure of the change in the interfacial thermodynamic activity of water molecules. An important issue is the possible emergence of a gel-like transient dissipative structure at the origin of the final elastic interface. [ABSTRACT FROM AUTHOR]

The correlation between interfacial properties and emulsion microstructure is a topic of special interest that has many industrial applications. This study deals with the comparison between the rheological properties of oil-water interfaces with adsorbed proteins from legumes (chickpea or faba bean) and the properties of the emulsions using them as the only emulsifier, both at microscopic (droplet size distribution) and macroscopic level (linear viscoelasticity). Two different pH values (2.5 and 7.5) were studied as a function of storage time. Interfaces were characterized by means of dilatational and interfacial shear rheology measurements. Subsequently, the microstructure of the final emulsions obtained was evaluated thorough droplet size distribution (DSD), light scattering and rheological measurements. Results obtained evidenced that pH value has a strong influence on interfacial properties and emulsion microstructure. The best interfacial results were obtained for the lower pH value using chickpea protein, which also corresponded to smaller droplet sizes, higher viscoelastic moduli, and higher emulsion stability. Thus, results put forward the relevance of the interfacial tension values, the adsorption kinetics, the viscoelastic properties of the interfacial film, and the electrostatic interactions among droplets, which depend on pH and the type of protein, on the microstructure, rheological properties, and stability of legume protein-stabilized emulsions.

The anionic surfactant sodium decyl sulfate (SDeS) at concentrations below its critical micellar concentration (cmc) was studied in a surface chemically purified state at the air–water interface in terms of its static and dynamic interfacial properties. Equilibrium surface tension was determined using a pendant drop tensiometer. An oscillating bubble capillary pressure tensiometer allowed accessing the surface dilatational properties of the surfactant's adsorption layers in a frequency range from 2 to 500 Hz. The estimation of single foam lamella stability was obtained from visual observation of films formed within a rectangular glass frame in a saturated atmosphere. Upon increasing surfactant concentration, the foam lamellae were found to rupture at prolonged lifetimes. The dramatic difference in foam stability goes along with a pronounced transition from a surface elastic to a surface visco-elastic state of the adsorption layers. These findings were indicative for a correlation between foam lamella stability and surface viscoelasticity also for this model surfactant. These results may be of importance to further shed light on the processes governing foam and foam lamella stability. [ABSTRACT FROM AUTHOR]

Dilatational rheology of a multi-component surfactant mixture at fluid-fluid interfaces is of importance for many real-life applications (biology, food products, crude oil production, etc.). However, although experimental data are easily measured, they cannot yet be analyzed in the framework of diffusional exchange between the surfactant solution and the interface when the number of the components exceeds two. Furthermore, although the single component analytical models exist for different interface geometries (flat, spherical, cylindrical), the binary mixture model is only available for a flat interface. To alleviate these limitations, a simple numerical scheme has been developed enabling the calculation of dilatational rheology with diffusional exchange for an n-component mixture in any geometry. The derived approach is limited to the case where relaxation is controlled by diffusion only and it relies on the matrix inversion of a set of first principle equations (mass conservation, diffusion and adsorption isotherm). Numerical solutions were validated against the exact analytical expression of both single component model and binary mixture dilatational rheology. [ABSTRACT FROM AUTHOR]

Polyhedral oligomeric silsesquioxanes (POSS) derivatives containing open silsesquioxane cage bear great potential for biomedical applications and therefore their lateral interactions with phospholipids, major biomembranes and drug vehicles constituent, should be studied in detail. That is why the properties of surface films by two POSS-derivatives, POSS-polyethylene glycol (POSS-PEG) and POSS-perfluoroalkyl (POSS-OFP), pure and in presence of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) were studied using Langmuir surface balance. Side chains of opposite nature (PEG is hydrophilic; OFP is hydrophobic) were selected, so that to evaluate their impact on polymers' surface properties. Two types of measurements were performed: (i) the miscibility of POSS-derivatives with DPPC was evaluated via thermodynamic analysis of the surface pressure (π)-area (A) isotherms and (ii) the dilatational rheology of selected POSS-polymer containing films was studied by the stress relaxation method. Fourier transformation analysis of the relaxation transients allows to access films' dynamic interfacial properties in broad frequency range (10 − 5 –1 Hz). Film morphology was monitored with Brewster Angle Microscopy. PEG moiety enabled POSS-PEG to stably incorporate in DPPC films, modifying their equilibrium and dynamic properties. In contrast OFP chains excluded from interactions with other molecules and diminished PEG-OFP amphiphilicity. Therefore at high packing densities (π ≥ 25 mN/m) PEG-OFP was expelled from the air/water interface in DPPC/PEG-OFP mixtures, and the binary films equilibrium and dynamic surface properties were determined primarily by DPPC. Thus the choice of POSS side chains can play key role in biomedical applications depending on whether strong or weak incorporation of POSS-polymers in lipid environment is aimed for. [ABSTRACT FROM AUTHOR]

Sodium dodecyl sulfate (SDS) is a well-defined model substance for anionic molecular surfactants. Aqueous mixtures of SDS in a surface chemically purified state and high purity NaCl were studied with respect to their equilibrium and dynamic surface tensions at a constant mean ionic activity I mean of 1 mmol L −1 . All studied solutions possessed the same equilibrium surface tension, however they showed striking differences in foam column and foam lamella stability experiments. This observation suggested the interpretation of the results in terms of dynamic interfacial properties. Oscillating bubble experiments were conducted to determine the frequency dependence of the surface dilatational modulus in a range from 5 to 400 Hz. The obtained surface dilatational modulus could be described by the extended Lucassen-van den Tempel (LvdT) model, which allows capturing dissipative processes by the intrinsic surface viscosity κ within the interfacial region. A new parameter derived from the fitting parameters of the LvdT model correlates reasonably with direct measurements of the solutions’ foam stability. The data suggest the important role of surface rheology for the stability of foams. [ABSTRACT FROM AUTHOR]

The surface properties of meibomian secretion (MGS), the major constituent of the tear film (TF) lipid layer, are of key importance for TF stability. The interfacial properties of canine, cMGS, and feline, fMGS, meibum films were studied using a Langmuir surface balance. These species were selected because they have blinking frequency and TF stability similar to those of humans. The sample's performance during dynamic area changes was evaluated by surface pressure ( π)-area ( A) isocycles and the layer structure was monitored with Brewster angle microscopy. The films' dilatational rheology was probed via the stress-relaxation technique. The animal MGS showed similar behavior both between each other and with human MGS (studied previously). They form reversible, non-collapsible, multilayer thick films. The relaxations of canine, feline, and human MGS films were well described by double exponential decay reflecting the presence of two processes: (1) fast elastic process, with characteristic time τ < 10 s and (2) slow viscous process, with τ > 100 s-emphasizing the meibum layers viscoelasticity. The temperature decrease from 35 to 25 °C resulted in decreased thickness and lateral expansion of all MGS layers accompanied with increase of the π/ A hysteresis and of the elastic process contribution to π relaxation transients. Thus, MGS films of mammals with similar blinking frequency and TF stability have similar surface properties and stress relaxations unaltered by the interspecies MGS compositional variations. Such knowledge may impact the selection of animal mimics of human MGS and on a better understanding of lipid classes' impact on meibum functionality. [ABSTRACT FROM AUTHOR]

Aim of the present study was to investigate the complex formation of β-lactoglobulin (β-LG) hydrolysates and different types of pectin at the oil/water-interface by dynamic interfacial pressure and the properties of the complexes by interfacial rheology (dilatation and shear). The degree of hydrolysis (DH) of β-LG was varied (3 and 6%) as well as the degree of methoxylation of the pectins, i.e. two low-(LMP, 32 and 35%) and two high-methoxylated (HMP, 64%) pectins were used. The pectins exhibited different local charge densities, due to enzyme specificity during demethoxylation. All experiments were performed at a constant biopolymer content (0.01 wt%), pH (4.0) and temperature (22 °C). β-LG/pectin interactions clearly delayed interfacial adsorption, which was more pronounced for LMP with a high local charge density. With increasing DH of β-LG, the interfacial adsorption was accelerated, however β-LG/pectin layers exhibited higher dilatational elastic moduli than hydrolysate/pectin layers. In contrast to dilatational rheology, β-LG formed weaker interfacial layers than its hydrolysates during shear time sweeps, despite the presence of pectin. Pectin and hydrolysates exhibited strong viscoelastic interfacial layers partially more than one order of magnitude higher than β-LG. However, during shear amplitude sweeps all interfacial layers were resistant to increasing strain and the films collapsed within the same region. Therefore, targeted structural modifications using enzymes with high specificity enables the production of β-LG hydrolysates and demethoxylated pectins with tailored functionality with respect to their interfacial rheology characteristics. [ABSTRACT FROM AUTHOR]

In recent years, pea protein isolate has received great attention due to its high nutritional value and multiple functional properties, among which emulsifying properties are one of the most important. However, the application of pea protein in food emulsions is still limited due to insufficient knowledge. As such, the aim of this study was to investigate the impact of environmental pHs (3, 7, 9) and different NaCl concentrations (20 mM, 100 mM) on the physicochemical and interfacial properties of green pea protein individual fractions (globulin, legumin, vicilin, and albumin) at the oil-water interface, and then to research their relationship with emulsifying properties. Results showed that compared to pH 7, samples treated with pH 9 and NaCl had faster initial adsorption (π 0), higher final interfacial pressure (π 10800) and rearrangement rate (K r), and better emulsifying ability, while samples treated with pH 3 had the opposite performance. Moreover, pH 9 emulsions were more stable, while NaCl weakened the emulsion, which was reflected in the first increase and then decrease of the interfacial dilatational viscoelasticity (E) induced by NaCl. Regarding the fraction effect, albumin and legumin subunit had the highest and lowest emulsifying ability, respectively. On the other hand, the emulsifying stability of albumin was most easily reduced by NaCl, as evidenced by the dramatically increased droplet size (from 1.62 to 28.92 and 72.00 μm), coalescence index (from 47.60 to 59.86 and 374.30%), and creaming index (from 3.43 to 8.00 and 12.71%). In all, while there is a limited relationship between the emulsifying properties of proteins and their solubility, surface hydrophobicity, secondary structure, and interfacial dilatational viscoelasticity, the interfacial pressure (π) was found to be positively related to the emulsifying ability, and K r was associated with both emulsifying ability and stability. The results could provide valuable information on the molecular mechanisms of emulsifying properties of pea protein fractions. [Display omitted] • Interfacial and emulsifying properties of pea protein fractions were investigated. • Legumin had the highest emulsifying ability (EA), but Albumin had the lowest EA. • EA and emulsifying stability of protein was associated with its rearrangement rate (Kr) and interfacial pressure. • pH 9.0 or NaCl treated samples had better EA due to faster adsorption(π 0) and Kr. [ABSTRACT FROM AUTHOR]

The surface dilatational modulus E is a fundamental system parameter of aqueous surfactant solutions which plays an important role in the physic of foams. In this contribution, we study the influence of highly charged Cerium-ions (Ce 4+ )-on the surface dilatational modulus E of aqueous sodium dodecyl sulfate (SDS) solutions. The E -modulus has been determined at two concentrations below the critical micellar concentration (cmc) in the frequency range from 3 Hz to 500 Hz using the oscillating bubble technique. The presence of Ce 4+ -ions increases the surface activity of the surfactant leading to a shift of the equilibrium surface tension isotherm to lower concentrations. The cmc is reduced to 2 × 10 −3 mol L −1 . Adsorption layers of aqueous SDS solutions exhibit a surface visco-elastic behavior. The magnitude and the phase of the complex dilatational modulus E increase in a continuous fashion with the frequency indicating a dissipative process within the adsorption layer. The presence of the electrolyte modifies the frequency characteristics of the complex modulus towards the features of a surface elastic system. Furthermore there are pronounced changes in the stability of the corresponding foams. The lifetime of wet foam lamella is significantly reduced by the presence of the Ce 4+ -ions. The results provide evidence for the decisive impact of surface visco-elastic properties on foam stability of aqueous surfactant solutions. [ABSTRACT FROM AUTHOR]

An analysis of the interfacial behaviour of two alternative protein derivatives with high solubility has been carried out at two different pH values (2 and 8). The protein derivatives (protein content higher than 50 wt.%) have a globular protein fraction mainly consisting of sarcoplasmic proteins (CFS); and a protein hydrolysate, (CFH), both obtained from crayfish surpluses. The physicochemical characterisation included protein solubility (higher than 80%) and surface charge as well as chemical analysis (elementary, sulfhydryl and disulphide groups). This was complemented with an interfacial characterization included measuring the surface pressure and surface dilatational measurements with a drop tensiometer, and interfacial shear rheology measurements performed using a double-wall-ring geometry. Whereas both types of protein derivative have significant interfacial activity (surface pressure between 20 and 40 mN/m), the difference in their behaviour is small In contrast, a strong influence of pH on the interfacial behaviour has been found for both soluble protein fractions. At pH 2, globular sarcoplasmic protein fraction yields lower surface pressures but highly viscoelastic interfaces, with 2D gel-like behaviour. At pH 8, on the other hand, CF proteins form quite rigid and more brittle interfaces, being resistant to dilatational deformations and showing high sensitivity to shear. [ABSTRACT FROM AUTHOR]

Asphaltenes are a fraction of crude oil that can stabilize undesirable water/crude oil emulsions. Only a small fraction of the asphaltenes plays an active role in emulsion stabilization and this fraction has a relatively high heteroatom content. However, the transient behavior and the microstructural evolution of these asphaltene fractions at the water/oil interfaces are not fully understood. In this study, interfacial rheology and microstructural evolution of Athabasca asphaltene and its subfractions at the water/toluene interface were studied using passive microrheology and dilatational rheology. Asphaltenes (labeled A) were fractionated based on their surface activity via an emulsion-based method to obtain interfacially active (IA) and partially active (PA) subfractions. The passive microrheology experiments demonstrated that the IA asphaltenes adsorbed much faster at the water/toluene interface than A and PA asphaltenes. The IA asphaltenes formed rigid interfacial films within a few minutes which fully immobilized the probe particles. The same adsorption trend was observed in the interfacial pressure measurements and dilatational rheology experiments. Particle tracking microrheology over the entire interface showed that, during the adsorption process, asphaltene films grew heterogeneously and eventually turned into homogeneous structures at longer aging times. The IA asphaltene films were more homogeneous than the other asphaltene films offering fewer weak points for coalescence. The drop size distributions in emulsions prepared using IA and PA asphaltene showed significant coalescence after 1.5 h in the PA fraction but not the IA fraction, confirming the ability of IA asphaltenes to stabilize emulsions. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Defatted wheat gluten proteins were subjected to a thermal process under mildly acidic conditions using 50–250 mM HCl. The degree of deamidation and hydrolysis reached in gluten proteins produced variable water-soluble fractions at neutral pH. When pH shifted from alkaline to acidic ranges, these fractions, in buffered aqueous media, developed different zeta potentials and different association/aggregation states. Interfacial rheological properties of water-soluble peptides were characterized by dilatational rheology at the air–water interface. A pendant drop tensiometer was used to produce harmonic perturbations to obtain the elastic component of the interfacial viscoelasticity modulus. Gluten proteins with the lowest degree of hydrolysis and deamidation, produced peptides with the highest interfacial elastic moduli of adsorbed films at the air–water interface. The mildly acidic treatment produced water-soluble peptides at neutral pH with different molecular weight profiles; a peptide fraction with molecular weight lower than 10 kDa increased with the increasing HCl concentration. [Copyright &y& Elsevier]

Highlights: [•] Adsorption of β-casein/β-lactoglobulin mixtures was studied at the O/W interface. [•] Transient interfacial tests and harmonic drop oscillations were performed. [•] Small amplitude oscillations evidenced a prevalent solid-like behaviour. [•] β-Casein mainly affects the adsorption and rheological properties of mixed layers. [ABSTRACT FROM AUTHOR]

Abstract: An emerging application of colloidal science is the design of foods that provide specific physiological responses, such as control of satiety and delivery of bioactive components to specific locations. Pluronics are known to hinder the access of lipase in the presence of bile salts to the lipid droplets owing to the formation of a steric barrier, thus delaying the rate of lipid digestion. The aim of this work is to advance into the understanding of the impact of Pluronics on lipid digestion. We have partially studied the effect of the lengths of the hydrophobic/hydrophilic chains on in-vitro digestion of interfacial layers of Pluronics adsorbed at the olive oil–water interface. Pluronics F127 and F68 were tested. F127 has a longer hydrophobic chain than F68, providing higher interfacial coverage at the same molar concentration, due to the adsorption of this portion onto the oil–water interface. F127 also has longer hydrophilic chains that remain in the aqueous phase leading to a greater steric bulky layer. F127 and F68 interfacial layers were selected to provide same interfacial tension, related to the interfacial coverage, but differing in the length of the steric bulky layer. The experiments have been carried out in a novel pendant drop film balance developed at the University of Granada (The OCTOPUS), which allows the simulation of the digestion process on a single droplet. A correlation between specific interfacial structure of two Pluronics and digestion rate is obtained from the interfacial response, importantly complementing the behaviour of emulsions found in previous work. The chosen Pluronic adsorbed layers showed similar resistance to lipase activity in the presence of bile salts, indicating the importance of the interfacial tension when controlling lipid digestion rate. These fundamental studies can have enormous implications towards the rational design of functional biointerfaces. [Copyright &y& Elsevier]

Highlights: [•] The combination of PDADMAC and TC4 enable microencapsulation of dodecane in PMMA. [•] Stabilization of the dodecane–PMMA interface leads to multicore morphology. [•] PDADMAC adsorbs strongly at the TC4 containing PMMA interface. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this work is to investigate the simultaneous adsorption of a globular protein, ovalbumin, and two different types of food emulsifiers, non-ionic Tween 60 and anionic Admul DATEM, at the air–water and sunflower oil–water interfaces. A commercial non-purified oil was used, aiming at investigating the behaviour of interfaces close to real systems. A pendant drop tensiometer was used to carry out transient interfacial tension measurements and small amplitude oscillations. A constant protein concentration (0.1 g/l) and different emulsifier/protein ratios (ranging between 0 and 0.6) were used during the tests. Experimental results evidenced that the non-ionic emulsifier replaces the protein on the interface (only a partial replacement was observed in the tested conditions) whereas the anionic molecule interacts with the protein forming complexes which can be almost completely replaced by the single emulsifier. The interfacial layers are characterised by a prevalent solid-like behaviour, which proved to be similar to 3D weakly structured systems. The rheological properties are strongly dependent on the nature of both the emulsifier and the interface, nevertheless it was observed that ovalbumin yields a more structured and stronger layer than Admul and Tween. In mixed systems, increasing the emulsifier concentration, the extension of this 2D network decreases whereas the strength seems to be less dependent and evidences only a slight reduction for Admul addition at the A/W interface. [Copyright &y& Elsevier]

Abstract: The effect of enzymatic hydrolysis and polysaccharide addition on the interfacial adsorption of β-lactoglobulin (β-LG) was investigated in this work. The enzymatic treatment was performed in the hydrolysis degree (HD) range of 0.0–5.0% using bovine α-chymotrypsin II immobilized on agarose beads. Anionic non-surface active polysaccharides (PS), sodium alginate (SA) and λ-carrageenan (λ-C) were studied in the concentration range of 0.0–0.5wt.%. The adsorption process at the air–water interface was evaluated by means of tensiometry and surface dilatational rheology. Biopolymer interactions in solution were analyzed by extrinsic fluorescence spectroscopy. The enzymatic hydrolysis improved β-LG interfacial properties. On the other hand, at low HD (1.0%), PS addition enhanced surface and elastic properties of β-LG hydrolysate films probably due to a higher repulsion between biopolymers in solution. However, at high HD (3.0–5.0%), SA addition caused a deterioration of surface and elastic properties of β-LG hydrolysate films probably due to the segregation and hydrolysate aggregation in solution, whereas λ-C addition could promote the formation of soluble complexes leading to a better control of elastic properties of β-LG hydrolysate films. [Copyright &y& Elsevier]

Abstract: Milk whey proteins (MWP) and pectins (Ps) are biopolymer ingredients commonly used in the manufacture of colloidal food products. Therefore, knowledge of the interfacial characteristics of these biopolymers and their mixtures is very important for the design of food dispersion formulations (foams and/or emulsions). In this paper, we examine the adsorption and surface dilatational behaviour of MWP/Ps systems under conditions in which biopolymers can saturate the air–water interface on their own. Experiments were performed at constant temperature (20°C), pH 7 and ionic strength 0.05M. Two MWP samples, β-lactoglobulin (β-LG) and whey protein concentrate (WPC), and two Ps samples, low-methoxyl pectin (LMP) and high-methoxyl pectin (HMP) were evaluated. The contribution of biopolymers (MWP and Ps) to the interfacial properties of mixed systems was evaluated on the basis of their individual surface molecular characteristics. Biopolymer bulk concentration capable of saturating the air–water interface was estimated from surface pressure isotherms. Under conditions of interfacial saturation, dynamic adsorption behaviour (surface pressure and dilatational rheological characteristics) of MWP/Ps systems was discussed from a kinetic point of view, in terms of molecular diffusion, penetration and configurational rearrangement at the air–water interface. The main adsorption mechanism in MWP/LMP mixtures might be the MWP interfacial segregation due to the thermodynamic incompatibility between MWP and LMP (synergistic mechanism); while the interfacial adsorption in MWP/HMP mixtures could be characterized by a competitive mechanism between MWP and HMP at the air–water interface (antagonistic mechanism). The magnitude of these phenomena could be closely related to differences in molecular composition and/or aggregation state of MWP (β-LG and WPC). [Copyright &y& Elsevier]

Abstract: The emulsifying properties and interfacial behaviour of conventional arabic gum (Acacia Senegal, control gum) and after thermal maturation (EM1 and EM2) were studied. All gums presented good oil in water emulsifying capacities. However, after 20–60 high-pressure homogenization passes, matured gums formed more homogenous emulsions with smaller mean oil droplets (0.4 μm) than the control gum (0.65 μm). Modification of pH from 4.5 to 7.0 did not affect sample characteristics. The film-forming capability of all samples at air–water interface was studied using adsorbed and spread techniques. The greater the amount and molecular mass of the arabinogalactan protein (AGP) component in the gum, the better the interfacial properties (tension drop kinetic and interfacial tension final values). Good dilatational elasticity was found for all three gums samples, corresponding to highly elastic interfacial films. The spread films of matured gum EM2 rearranged during compression, passing through liquid expanded, liquid condensed into solid states. Conversely, control and EM1 gums only formed liquid expanded films and smaller surface coverage than EM2. Analytical interfacial results confirm the improved emulsifying properties of matured gums. The properties of the AGP molecules in the gums could be responsible for these differences. [Copyright &y& Elsevier]