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.
Effect of cinnamaldehyde on interfacial rheological properties of proteins adsorbed at O/W interfaces
Felix Angel, Manuel ; Yang, J. ; Guerrero, A. ; Sagis, L.M.C. - \ 2019
Food Hydrocolloids 97 (2019). - ISSN 0268-005X
Dilatational - Lissajous - LAOD - Interfacial shear
The dynamics of heterogeneous food products such as emulsions can be affected significantly by the interfacial properties of their interfaces. Proteins are widely used to increase the stability of these food products. This work compares the interfacial properties of a model protein (whey protein isolate, WPI) and silkworm pupae (SLW) adsorbed at the O/W interface. A natural aldehyde (cinnamaldehyde, CNM) was used for both protein systems in order to promote protein-protein interactions. Interfacial properties were characterised during protein adsorption and after reaching a quasi-equilibrium state by means of oscillatory and step dilatational, and oscillatory interfacial shear measurements. The results obtained from dilatational and interfacial shear tests showed that the use of CNM resulted in the development of stronger interfaces, with higher values for the dilatational and surface shear storage moduli, and a lower loss tangent. Step-dilatation tests indicated that the addition of CNM also resulted in more homogeneous interfaces. Our results show that CNM addition can enhance the surface properties of SLW, to a level which is close to the properties of un-modified WPI stabilized interfaces.