DNA Penetration into a Lysozyme Layer at the Surface of Aqueous Solutions.

The interactions of DNA with lysozyme in the surface layer were studied by performing infrared reflection-absorption spectroscopy (IRRAS), ellipsometry, surface tensiometry, surface dilational rheology, and atomic force microscopy (AFM). A concentrated DNA solution was injected into an aqueous subphase underneath a spread lysozyme layer. While the optical properties of the surface layer changed fast after DNA injection, the dynamic dilational surface elasticity almost did not change, thereby indicating no continuous network formation of DNA/lysozyme complexes, unlike the case of DNA interactions with a monolayer of a cationic synthetic polyelectrolyte. A relatively fast increase in optical signals after a DNA injection under a lysozyme layer indicates that DNA penetration is controlled by diffusion. At low surface pressures, the AFM images show the formation of long strands in the surface layer. Increased surface compression does not lead to the formation of a network of DNA/lysozyme aggregates as in the case of a mixed layer of DNA and synthetic polyelectrolytes, but to the appearance of some folds and ridges in the layer. The formation of more disordered aggregates is presumably a consequence of weaker interactions of lysozyme with duplex DNA and the stabilization, at the same time, of loops of unpaired nucleotides at high local lysozyme concentrations in the surface layer.

Investigating the Influence of Polysorbate 20/80 and Polaxomer P188 on the Surface & Interfacial Properties of Bovine Serum Albumin and Lysozyme.

PURPOSE: To provide new insights into how protein-surfactant competitive adsorbtion and corresponding surface tension reduction properties at the air-water and oil-water interface are impacted by the type of protein and the associated protein surface rheology. METHOD: Interfacial Rheology was utilized to obtain surface G' and G" as a function of frequency. Force tensiometry was utilized to obtain changes in surface tension as a function of surfactant concentration. The impact on surface properties of two different proteins i.e. BSA and Lysozyme was investigated as a function of surfactant concentration i.e. polysorbates PS 20, PS 80 and Poloxomer (Kolliphor P188). RESULTS: Surface tension and interfacial tension measurements for BSA showed that in mixed BSA/polysorbate surfactant systems, BSA dominates the interfacial behavior at both the air-water and oil-water interfaces, until a high polysorbate concentration of 0.1 mg/ml. At these high polysorbate concentrations a mixed BSA-Polysorbate interfacial layer is formed as corroborated by the surface elasticity values being lower than that of pure BSA but higher than that of pure Polysorbate. For Kolliphor, it was observed that Kolliphor was unable to displace BSA at any concentration. This is corroborated by the high surface elasticity of the BSA which is maintained in the presence of Kolliphor. Surface and interfacial tension measurements for lysozyme show that for mixed lysozyme/polysorbate surfactant systems, the surface tension values are lower than that exhibited by either the lysozyme or the polysorbate surfactants. This potentially indicates the formation of a mixed layer of lysozyme and polysorbate. At the high polysorbate concentrations probed, the surface elasticity values are however closer to that of pure polysorbates, indicating that the mixed layer may be more heavily polysorbate dominated, especially at high polysorbate concentrations. For Kolliphor, the response was similar to that seen in the Kolliphor-BSA system in which the Kolliphor was not able to displace the protein i.e. Lysozyme. CONCLUSIONS: In conclusion, it was seen that competitive adsorption between proteins and common excipient surfactants is dictated by the type of protein and its effective structuring/rigidity at the surface as reflected through surface elasticity and surface tan delta values. BSA was seen to exhibit a higher surface elasticity than lysozyme, and therefore has a more rigid structure and is more competitive at the interface.

Physicochemical studies of direct interactions between lung surfactant and components of electronic cigarettes liquid mixtures.

Direct physicochemical interactions between the major components of electronic cigarette liquids (e-liquids): glycerol (VG) and propylene glycol (PG), and lung surfactant (LS) were studied by determining the dynamic surface tension under a simulated breathing cycle using drop shape method. The studies were performed for a wide range of concentrations based on estimated doses of e-liquid aerosols (up to 2500 × the expected nominal concentrations) and for various VG/PG ratios. The results are discussed as relationships among mean surface tension, surface tension amplitude, and surface rheological properties (dilatational elasticity and viscosity) versus concentration and composition of e-liquid. The results showed that high local concentrations (>200 × higher than the estimated average dose after a single puffing session) may induce measurable changes in biophysical activity of LS; however, only ultra-high e-liquid concentrations inactivated the surfactant. Physiochemical characterization of e-liquids provide additional insights for the safety assessment of electronic nicotine delivery systems (ENDS).

Complexation of phospholipids and cholesterol by triterpenic saponins in bulk and in monolayers.

The interactions between three triterpene saponins: α-hederin, hederacoside C and ammonium glycyrrhizate with model lipids: cholesterol and dipalmitoylphosphatidylcholine (DPPC) are described. The oleanolic acid-type saponins (α-hederin and hederacoside C) were shown to form 1:1 complexes with lipids in bulk, characterized by stability constants in the range (4.0±0.2)·10(3)-(5.0±0.4)·10(4) M(-1). The complexes with cholesterol are generally stronger than those with DPPC. On the contrary, ammonium glycyrrhizate does not form complexes with any of the lipids in solution. The saponin-lipid interactions were also studied in a confined environment of Langmuir monolayers of DPPC and DPPC/cholesterol with the saponins present in the subphase. A combined monolayer relaxation, surface dilational rheology, fluorescence microscopy and neutron reflectivity (NR) study showed that all three saponins are able to penetrate pure DPPC and mixed DPPC/cholesterol monolayers. Overall, the effect of the saponins on the model lipid monolayers does not fully correlate with the lipid-saponin complex formation in the homogeneous solution. The best correlation was found for α-hederin, for which even the preference for cholesterol over DPPC observed in bulk is well reflected in the monolayer studies and the literature data on its membranolytic activity. Similarly, the lack of interaction of ammonium glycyrrhizate with both lipids is evident equally in bulk and monolayer experiments, as well as in its weak membranolytic activity. The combined bulk and monolayer results are discussed in view of the role of confinement in modulating the saponin-lipid interactions and possible mechanism of membranolytic activity of saponins.

Effect of cholesterol nanodomains on monolayer morphology and dynamics.

At low mole fractions, cholesterol segregates into 10- to 100-nm-diameter nanodomains dispersed throughout primarily dipalmitoylphosphatidylcholine (DPPC) domains in mixed DPPC:cholesterol monolayers. The nanodomains consist of 6:1 DPPC:cholesterol "complexes" that decorate and lengthen DPPC domain boundaries, consistent with a reduced line tension, λ. The surface viscosity of the monolayer, ηs, decreases exponentially with the area fraction of the nanodomains at fixed surface pressure over the 0.1- to 10-Hz range of frequencies common to respiration. At fixed cholesterol fraction, the surface viscosity increases exponentially with surface pressure in similar ways for all cholesterol fractions. This increase can be explained with a free-area model that relates ηs to the pure DPPC monolayer compressibility and collapse pressure. The elastic modulus, G', initially decreases with cholesterol fraction, consistent with the decrease in λ expected from the line-active nanodomains, in analogy to 3D emulsions. However, increasing cholesterol further causes a sharp increase in G' between 4 and 5 mol% cholesterol owing to an evolution in the domain morphology, so that the monolayer is elastic rather than viscous over 0.1-10 Hz. Understanding the effects of small mole fractions of cholesterol should help resolve the controversial role cholesterol plays in human lung surfactants and may give clues as to how cholesterol influences raft formation in cell membranes.

Unusual penetration of phospholipid mono- and bilayers by Quillaja bark saponin biosurfactant.

The interactions between a model phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and a biosurfactant Quillaja Bark Saponin (QBS) obtained from the bark of Quillaja saponaria Molina were studied using simple models of biological membranes. QBS is known to interact strongly with the latter, exerting a number of haemolytic, cytotoxic and anti-microbial actions. The interaction of QBS dissolved in the subphase with DPPC monolayers and silicon-supported bilayers was studied above the cmc (10(-3)M). Surface pressure relaxation and surface dilatational rheology combined with quartz crystal microbalance (QCM) and neutron reflectivity (NR) were employed for this purpose. The DPPC-penetrating abilities of QBS are compared with those of typical synthetic surfactants (SDS, CTAB and Triton X-100). We show that the penetration studies using high surface activity (bio)surfactants should be performed by a subphase exchange, not by spreading onto the surfactant solution. In contrast to the synthetic surfactants of similar surface activity, QBS does not collapse DPPC mono- and bilayers, but penetrates them, improving their surface dilatational elastic properties even in the highly compressed solid state. The dilatational viscoelasticity modulus increases from 204 mN/m for pure DPPC up to 310 mN/m for the QBS-penetrated layers, while it drops to near zero values in the case of the synthetic surfactants. The estimated maximum insertion pressure of QBS into DPPC monolayers exceeds the maximum surface pressure achievable in our setup, in agreement with the surface rheological response of the penetrated layers.

Dynamic properties of the layers of cupin-1.1 aggregates at the air/water interface.

Spread layers of amorphous aggregates of the structural domain of plant protein vicilin, cupin-1.1, at the water - air interface were studied by the surface tensiometry, dilational surface rheology, Brewster angle and atomic force microscopy. The layer properties differed strongly from the results for the layers of previously studied proteins. The dependency of the dynamic elasticity of the layer on surface pressure had two local maxima with the second peak being four times higher than the first one. In the region of the first maximum the obtained results are similar to those for dispersions of polymer microgels with a hairy corona. At the beginning of surface compression separate threads of the corona are stretched along the surface and the surface elasticity increases. The further compression results in the formation of loops and tails leading to a decrease of the elasticity. The second local maximum of the dynamic surface elasticity is presumably caused by the interactions of the rigid cores of the aggregates leading finally to the formation of multilayer structures at high surface pressures. In this case, the surface elasticity starts to decrease as a result of the segment exchange between different layers at the interface.

The silicone depletion in combination products induced by biologics.

Silicone oil (SO) migration into the drug product of combination products for biopharmaceuticals during storage is a common challenge. As the inner barrel surface is depleted of SO the extrusion forces can increase compromising the container functionality. In this context we investigated the impact of different formulations on the increase in gliding forces in a spray-on siliconized pre-filled syringe upon storage at 2-8 °C, 25 °C and 40 °C for up to 6 months. We tested the formulation factors such as surfactant type, pH, and ionic strength in the presence of one monoclonal antibody (mAb) as well as compared three mAbs in one formulation. After 1 month at 40 °C, the extrusion forces were significantly increased due to SO detachment dependent on the fill medium. The storage at 40 °C enhanced the SO migration process but it could also be observed at lower storage temperatures. Regarding the formulation factors the tendency for SO migration was predominantly dependent on the presence and type of surfactant. Interestingly, when varying the mAb molecules, one of the proteins showed a rather stabilizing effect on the SO layer resulting into higher container stability. In contrast to the formulation factors, those different stability outcomes could not be explained by interfacial tension (IFT) measurements at the SO interface. Further characterization of the mAb molecules regarding interfacial rheology and conformational stability were not adequately able to explain the observed difference. Solely a hydrophobicity ranking of the molecules correlated to the stability outcome. Further investigations are needed to clarify the role of the protein in the SO detachment process and to understand the cause for the stabilization. However, the study clearly demonstrated that the protein itself plays a critical role in the SO detachment process and underlined the importance to include verum for container stability.

Oil-water interface and emulsion stabilising properties of rapeseed proteins napin and cruciferin studied by nonlinear surface rheology.

HYPOTHESIS: Two major protein families are present in rapeseed, namely cruciferins and napins. The structural differences between the two protein families indicate that they might behave differently when their mixture stabilises oil-water interfaces. Therefore, this work focuses on elucidating the role of both proteins in interface and emulsion stabilisation. EXPERIMENTS: Protein molecular properties were evaluated, using SEC, DSC, CD, and hydrophobicity analysis. The oil-water interface mechanical properties were studied using LAOS and LAOD. General stress decomposition (GSD) was used as a novel method to characterise the nonlinear response. Additionally, to evaluate the emulsifying properties of the rapeseed proteins, emulsions were prepared using pure napins or cruciferin and also their mixtures at 1:3, 1:1 and 3:1 (w:w) ratios. FINDINGS: Cruciferins formed stiff viscoelastic solid-like interfacial layers (Gs' = 0.046 mN/m; Ed' = 30.1 mN/m), while napin formed weaker and more stretchable layers at the oil-water interface (Gs' = 0.010 mN/m; Ed' = 26.4 mN/m). As a result, cruciferin-formed oil droplets with much higher stability against coalescence (coalescence index, CI up to 10%) than napin-stabilised ones (CI up to 146%) during two months of storage. Both proteins have a different role in emulsions produced with napin-cruciferin mixtures, where cruciferin provides high coalescence stability, while napin induces flocculation. Our work showed the role of each rapeseed protein in liquid-liquid multiphase systems.

Breakups of Chitosan microcapsules in extensional flow.

The controlled rupture of a core-shell capsule and the timely release of encapsulated materials are essential steps of the efficient design of such carriers. The mechanical and physico-chemical properties of their shells (or membranes) mainly govern the evolution of such systems under stress and notably the link between the dynamics of rupture and the mechanical properties. This issue is addressed considering weakly cohesive shells made by the interfacial complexation of Chitosan and PFacid in a planar extensional flow. Three regimes are observed, thanks to the two observational planes. Whatever the time of reaction in membrane assembly, there is no rupture in deformation as long as the hydrodynamic stress is below a critical value. At low times of complexation (weak shear elastic modulus), the rupture is reminiscent of the breakup of droplets: a dumbell or a waist. Fluorescent labelling of the membrane shows that this process is governed by continuous thinning of the membrane up to the destabilization. It is likely that the membrane shows a transition from a solid to liquid state. At longer times of complexation, the rupture has a feature of solid-like breakup (breakage) with a discontinuity of the membrane. The maximal internal constraint determined numerically marks the initial location of breakup as shown. The pattern becomes more complex as the elongation rate increases with several points of rupture. A phase diagram in the space parameters of the shear elastic modulus and the hydrodynamic stress is established.

Dynamic interfacial properties and foam behavior of licorice root extract solutions.

Licorice (Glycyrrhiza glabra) is a useful plant of the family Fabaceae, with sweet-tasting roots. The root extract of this plant is rich in saponins, so it can be considered a source of natural surfactants. This research provides some applicable information about the dynamic surface tension and foam behavior of aqueous solutions of licorice root extract (LRE). The pendant drop shape analysis was utilized to study the surface tension and dilational surface rheology of LRE at the water/air interface. The Bikerman type experiment was used to measure foamability and foam stability of aqueous LRE solutions. The equilibrium surface tensions reveal that the LRE contains surface-active components and is capable of reducing the surface tension by 25 mN/m at the critical aggregation concentration (CAC). The surface dilational visco-elasticity measurements proved that the adsorption layers are predominantly of elastic nature. Also the foamability and foam stability show a meaningful correlation with the dynamic surface properties. This study aims to contribute to the development of appropriate utilization of the benefits provided by a biosurfactant source in foam-related commercial applications.

Surface tension of native and modified plant seed proteins.

The present review, dedicated to Prof. Zbigniew Adamczyk on the occasion of his 70th anniversary, covers the literature data on surface tension and surface compression (dilational) rheology of the adsorbed layers of 21 plant seed proteins (10 leguminous and 11 non-leguminous plants). They are typically analyzed as protein concentrates or isolates, the latter usually obtained by isoelectric precipitation or diafiltration. Despite generally lower solubility, as compared to their animal counterparts (lactoglobulins, caseins, albumins, etc.), the plant seed proteins are also capable of lowering surface tension and forming viscoelastic adsorbed layers. Many seed proteins serve mostly as amino acids reservoirs for the future seedling (storage proteins), hence their instantaneous amphiphilicity is not always sufficient to induce strong adsorption at the aqueous-air interface. They can be, however, conveniently unfolded, hydrolyzed and/or chemically/enzymatically modified to expose more hydrophilic or hydrophobic patches. As shown in numerous contributions reviewed below, the resulting shift of the hydrophilic-lipophilic balance can boost their surface activity to the level comparable to that of many animal proteins or low molecular weight surfactants. An important advantage of the plant seed proteins over the animal ones is their much lower environmental cost and abundance in many plants (e.g. ~40% in sunflower or soybean seeds).

Impact of denaturing agents on surface properties of myoglobin solutions.

The addition of denaturants strongly influences the surface properties of aqueous myoglobin solutions. The effect differs from the results for mixed solutions of the denaturants and other globular proteins, for example, bovine serum albumin (BSA), lysozyme and ß-lactoglobulin (BLG), although the surface properties of the solutions of the pure proteins are similar. The kinetic dependencies of the dynamic surface elasticity of myoglobin solutions with guanidine hydrochloride (GuHCl) reveal at least two adsorption steps at denaturant concentrations higher than 1 M: a very fast increase of the dynamic surface elasticity to approximately 30 mN/m at the beginning of adsorption, and a slower growth to abnormally high values of 250-300 mN/m. At the same time, the surface elasticity of BSA/GuHCl, BLG/GuHCl and lysozyme/GuHCl solutions is a non-monotonic function of the surface age, and does not exceed 50 mN/m close to equilibrium. The high surface elasticity of myoglobin/GuHCl solutions may be associated with protein aggregation in the surface layer. The formation of aggregates is confirmed by ellipsometry and Brewster angle microscopy. The addition of ionic surfactants to protein solutions leads to the formation of myoglobin/surfactant complexes, and the kinetic dependencies of the dynamic surface elasticity display local maxima indicating multistep adsorption kinetics, unlike the corresponding results for solutions of other globular proteins mixed with ionic surfactants. Ellipsometry and infrared reflection-absorption spectroscopy allow tracing the adsorption of the complexes and their displacement from the interface at high surfactant concentrations.

Stability of Foams in Vacuum Drying Processes. Effects of Interactions between Sugars, Proteins, and Surfactants on Foam Stability and Dried Foam Properties.

The hypothesis was that saccharides mediate interactions between surface-active components and that this will have an impact on foam decay during the drying process. Static light scattering was performed to determine changes in interactions between the foam stabilizer on a molecular level. Furthermore, pendant drop and oscillating drop measurements were performed to examine the surface tension and surface rheology. Foams were dried in conventional dryers as well as microwave-supported vacuum dryers. Final foam properties were determined. It was shown that the addition of sugars, often added as protective substances for sensitive organic molecules, resulted in lower repulsion between different types of surface-active components, namely polysorbate 80 and ß-lactoglobulin (ß-lg). Differences in impact of the types of sugars and between different types of surfactant, protein, and small molecules were observed influencing the foam decay behavior. The interfacial properties of polysorbate 80 and ß-lg were influenced by the type of the used sugars. The surface elasticity of protein stabilized surfaces was higher compared to that of polysorbate stabilized systems. Protein stabilized systems remained more stable compared to polysorbate systems, which was also affected by the used saccharide. Overall, a correlation between molecular interactions and foam decay behavior was found.

Air-water interfacial behaviour of whey protein and rapeseed oleosome mixtures.

HYPOTHESIS: Plant seeds store lipids in oleosomes, which are storage organelles with a triacylglycerol (TAG) core surrounded by a phospholipid monolayer and proteins. Due to their membrane components, oleosomes have an affinity for the air/oil-water interface. Therefore, it is expected that oleosomes can stabilise interfaces, and also compete with proteins for the air-water interface. EXPERIMENTS: We mixed rapeseed oleosomes with whey protein isolate (WPI), and evaluated their air-water interfacial properties by interfacial rheology and microstructure imaging. To understand the contribution of the oleosome components to the interfacial properties, oleosome membrane components (phospholipids and membrane proteins) or rapeseed lecithin (phospholipids) were also mixed with WPI. FINDINGS: Oleosomes were found to disrupt after adsorption, and formed TAG/phospholipid-rich regions with membrane fragments at the interface, forming a weak and mobile interfacial layer. Mixing oleosomes with WPI resulted in an interface with TAG/phospholipid-rich regions surrounded by whey protein clusters. Membrane components or lecithin mixed with proteins also resulted in an interface where WPI molecules aggregated into small WPI domains, surrounded by a continuous phase of membrane components or phospholipids. We also observed an increase in stiffness of the interfacial layer, due to the presence of oleosome membrane proteins at the interface.

Light scattering by liquid surfaces, new developments.

The surface light scattering technique is presented, highlighting recent technical improvements and describing studies of various types of surfaces. The technique is non-invasive, but delicate to handle and no commercial instruments are available yet. The technique gives however interesting information difficult to obtain otherwise, for instance on out-of-equilibrium surfaces, surfaces of very low tension, or systems close to solidification. Many studies were performed with monolayers of surface-active molecules at the surface of water. In this case, surface viscoelastic parameters can be determined at high frequencies (10 kHz- 1 MHz), complementing usefully the data obtained at lower frequencies with other techniques. As with these other techniques, inconsistencies such as negative surface viscosities are sometimes reported. The origin of these anomalies is not yet fully clarified. The problem deserves further work, in order to achieve a satisfactory description of the motion of surfactant or polymer-laden surfaces.

DNA Interaction with a Polyelectrolyte Monolayer at Solution-Air Interface.

The formation of ordered 2D nanostructures of double stranded DNA molecules at various interfaces attracts more and more focus in medical and engineering research, but the underlying intermolecular interactions still require elucidation. Recently, it has been revealed that mixtures of DNA with a series of hydrophobic cationic polyelectrolytes including poly(N,N-diallyl-N-hexyl-N-methylammonium) chloride (PDAHMAC) form a network of ribbonlike or threadlike aggregates at the solution-air interface. In the present work, we adopt a novel approach to confine the same polyelectrolyte at the solution-air interface by spreading it on a subphase with elevated ionic strength. A suite of techniques-rheology, microscopy, ellipsometry, and spectroscopy-are applied to gain insight into main steps of the adsorption layer formation, which results in non-monotonic kinetic dependencies of various surface properties. A long induction period of the kinetic dependencies after DNA is exposed to the surface film results only if the initial surface pressure corresponds to a quasiplateau region of the compression isotherm of a PDAHMAC monolayer. Despite the different aggregation mechanisms, the micromorphology of the mixed PDAHMAC/DNA does not depend noticeably on the initial surface pressure. The results provide new perspective on nanostructure formation involving nucleic acids building blocks.

Role of interfacial elasticity for the rheological properties of saponin-stabilized emulsions.

HYPOTHESIS: Saponins are natural surfactants which can provide highly viscoelastic interfaces. This property can be used to quantify precisely the effect of interfacial dilatational elasticity on the various rheological properties of bulk emulsions. EXPERIMENTS: We measured the interfacial dilatational elasticity of adsorption layers from four saponins (Quillaja, Escin, Berry, Tea) adsorbed on hexadecane-water and sunflower oil-water interfaces. In parallel, the rheological properties under steady and oscillatory shear deformations were measured for bulk emulsions, stabilized by the same saponins (oil volume fraction between 75 and 85%). FINDINGS: Quillaja saponin and Berry saponin formed solid adsorption layers (shells) on the SFO-water interface. As a consequence, the respective emulsions contained non-spherical drops. For the other systems, the interfacial elasticities varied between 2 mN/m and 500 mN/m. We found that this interfacial elasticity has very significant impact on the emulsion shear elasticity, moderate effect on the dynamic yield stress, and no effect on the viscous stress of the respective steadily sheared emulsions. The last conclusion is not trivial, because the dilatational surface viscoelasticity is known to have strong impact on the viscous stress of steadily sheared foams. Mechanistic explanations of all observed effects are described.

Adsorption layer formation in dispersions of protein aggregates.

The review discusses recent results on the adsorption of amyloid fibrils and protein microgels at liquid/fluid interfaces. The application of the shear and dilational surface rheology, atomic force microscopy and passive particle probe tracking allowed for elucidating characteristic features of the protein aggregate adsorption while some proposed hypothesis still must be examined by special methods for structural characterization. Although the distinctions of the shear surface properties of dispersions of protein aggregates from the properties of native protein solutions are higher than the corresponding distinctions of the dilational surface properties, the latter ones give a possibility to obtain new information on the formation of fibril aggregates at the water/air interface. Only the adsorption of BLG microgels and fibrils was studied in some details. The kinetic dependencies of the dynamic surface tension and dilational surface elasticity for aqueous dispersions of protein globules, protein microgels and purified fibrils are similar if the system does not contain flexible macromolecules or flexible protein fragments. In the opposite case the kinetic dependencies of the dynamic surface elasticity can be non-monotonic. The solution pH influences strongly the dynamic surface properties of the dispersions of protein aggregates indicating that the adsorption kinetics is controlled by an electrostatic adsorption barrier if the pH deviates from the isoelectric point. A special section of the review considers the possibility to apply kinetic models of nanoparticle adsorption to the adsorption of protein aggregates.

Foaming Properties and Linear and Nonlinear Surface Dilatational Rheology of Sodium Caseinate, Tannin Acid, and Octenyl Succinate Starch Ternary Complex.

In this paper, the foaming and surface properties of sodium caseinate (SC), sodium caseinate/tannin acid (SC/TA), sodium caseinate/octenyl succinate starch (SC/OSA-starch), and sodium caseinate/tannin acid/octenyl succinate starch (SC/TA/OSA-starch) complex systems are described. First, foaming properties of different samples were compared at pH 6.0. The interface adsorption and linear surface dilatational rheological of different samples were characterized in the linear viscoelastic region to explore the relationship between macroscopic foaming properties and surface properties. At equal protein concentrations, the foamability and foam stability of the SC/TA/OSA-starch complex was markedly higher than that of the SC/TA complex. Meanwhile, the surface properties of the SC/TA/OSA-starch complex were also superior to those of the SC/TA complex. Finally, to investigate the nonlinear surface dilatational rheological behavior of the air/water interface stabilized by complex systems, the large-amplitude oscillatory dilatational rheology and Lissajous plots were studied. For the SC/TA/OSA-starch complex, the OSA-starch increases the degree of strain softening in extension, suggesting that the surface structure may change from a surface gel to a mixed phase of SC/TA patches and OSA-starch domains. These findings indicate that the complex formed between polyphenols, proteins, and polysaccharides could be used as a good alternative to understand and, consequently, improve the surface and foaming properties in food matrices.