Origin of the extremely high elasticity of bulk emulsions, stabilized by Yucca Schidigera saponins
Tsibranska, Sonya ; Tcholakova, Slavka ; Golemanov, Konstantin ; Denkov, Nikolai ; Arnaudov, Luben ; Pelan, Eddie ; Stoyanov, Simeon D. - \ 2020
Food Chemistry 316 (2020). - ISSN 0308-8146
Drop aggregation - Drop-drop adhesion - Emulsion - Emulsion elasticity - Interfacial elasticity - Non-purified oil - Phytosterols - Saponin
We found experimentally that the elasticity of sunflower oil-in-water emulsions (SFO-in-W) stabilized by Yucca Schidigera Roezl saponin extract, is by >50 times higher as compared to the elasticity of common emulsions. We revealed that strong specific interactions between the phytosterols from the non-purified oil and the saponins from the Yucca extract lead to the formation of nanostructured adsorption layers which are responsible for the very high elasticity of the oil-water interface and of the respective bulk emulsions. Remarkably, this extra high emulsion elasticity inhibits the emulsion syneresis even at 65 vol% of the oil drops – these emulsions remain homogeneous and stable even after 30 days of shelf-storage. These results demonstrate that the combination of saponin and phytosterols is a powerful new approach to structure oil-in-water emulsions with potential applications for formulating healthier functional food.
Role of interfacial elasticity for the rheological properties of saponin-stabilized emulsions
Tsibranska, Sonya ; Tcholakova, Slavka ; Golemanov, Konstantin ; Denkov, Nikolai ; Pelan, Eddie ; Stoyanov, Simeon D. - \ 2020
Journal of Colloid and Interface Science 564 (2020). - ISSN 0021-9797 - p. 264 - 275.
Emulsion - Emulsion rheology - Interfacial rheology - Saponin - Surface elasticity - Surface rheology
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.
Interfacial rheology and relaxation behavior of adsorption layers of the triterpenoid saponin Escin
Giménez-Ribes, Gerard ; Habibi, Mehdi ; Sagis, Leonard M.C. - \ 2020
Journal of Colloid and Interface Science 563 (2020). - ISSN 0021-9797 - p. 281 - 290.
Dilatational - Escin - Interfacial rheology - Non-linear Viscoelastic (NLVE) regime - Relaxation - Saponin - Shear - Stretched exponential
Hypothesis: Escin, a monodesmosidic triterpenoid saponin, was shown previously to form viscoelastic interfaces with a very high dilatational and surface shear storage modulus. This is expected to be due to the arrangement of Escin into 2D disordered soft viscoelastic solid interfacial structures, which results in turn in a distribution of relaxation times. Experiments: The responses to dilatational and surface shear deformations of Escin-stabilized air-water interfaces were studied, both in the linear viscoelastic (LVE) and non-linear (NLVE) regime. Step relaxation and amplitude sweeps were performed in dilatation experiments. For surface shear, amplitude sweeps and creep recovery experiments were performed. Findings: Escin stabilized-interfaces displayed a highly non-linear behavior in dilatation as seen in the Lissajous plots. In large oscillatory shear the Lissajous curves had a rhomboidal shape, indicating intracycle yielding and recovery, typical of glassy systems. The relaxation of the interface showed stretched exponential behavior, with stretched exponents typical of disordered solids with dynamic heterogeneity. The use of surface rheological measurements beyond the commonly measured LVE regime clearly has provided new insights into the behavior of these interfaces and their microstructure. These results highlight the need to reconsider other complex interfaces as disordered solids and not as 2D homogenous viscoelastic fluids.
Neutrophils and macrophage cell count in the gut area of zebrafish larvae treated with antibiotics or saponin or a combination of treatments
Lopez Nadal, Adria ; Brugman, Sylvia - \ 2019
Wageningen University & Research
Ciprofloxacin - Macrophages - Microbiota - Neutrophils - Oxytetracycline - Saponin - Zebrafish
This data set contains data collected during zebrafish larvae experiments at the Wageningen University as part of Adrià López Nadal PhD Thesis. This study corresponds to the article: “Exposure to Antibiotics Affects Saponin Immersion-Induced Immune Stimulation and Shift in Microbial Composition in Zebrafish Larvae” published in Frontiers in Microbiology the 29th of October 2018.
Role of surface properties for the kinetics of bubble Ostwald ripening in saponin-stabilized foams
Tcholakova, Slavka ; Mustan, Fatmegul ; Pagureva, Nevena ; Golemanov, Konstantin ; Denkov, Nikolai D. ; Pelan, Edward G. ; Stoyanov, Simeon D. - \ 2017
Colloids and Surfaces. A: Physicochemical and Engineering Aspects 534 (2017). - ISSN 0927-7757 - p. 16 - 25.
Adsorption layer - Foam coarsening - Ostwald ripening - Saponin - Surface rheology
Bubble Ostwald ripening (OR) leads to a gradual increase of the mean bubble size in foams with time. The rate of OR can be reduced significantly or even arrested completely using appropriate solid particles and/or surfactants as foam stabilizers. In the current paper, we show that saponins, a widespread class of natural surfactants, can reduce significantly the rate of OR in foams. To reveal the reasons for the reduced rate of OR in saponin-stabilized foams, we performed measurements of the rate of bubble diminishing, for single air bubbles placed below a solution surface, with a series of saponin bio-surfactants. These saponin surfactants form adsorption layers with surface elasticity, spanning a very wide range - from almost zero up to several thousand mN/m. The measured rate of bubble OR showed no correlation with the surface elastic modulus (dilatational or shear), as measured at 0.1. Hz frequency of surface oscillations. A reasonable correlation was observed only with the surface stress (deviation from the equilibrium surface tension), measured at very slow rate of surface deformation, which mimics much better the actual processes of bubble OR in foams - higher surface stress corresponds to lower OR rate. New theoretical expression, accounting for the out-of- equilibrium surface tension during bubble shrinkage and for the gas flux across the meniscus regions surrounding the foam films, was derived and used to calculate theoretically the rate of bubble diminishing. The comparison of the theoretical predictions with the experimental data shows clearly that the main reason for the reduced rate of OR in the studied systems is the high resistance to gas transfer of the saponin adsorption layers. The deviations from the equilibrium surface tension, although noticeable, have smaller effect. The complementary experiments with actual foams showed that the rate of OR is even lower (compared to the rate measured with single bubbles) which is explained with the thicker non-equilibrium foam films, formed between the neighboring bubbles in saponin-stabilized foams.