Adsorption of Saponin and Saponin–Chitosan Mixture at Water–Oil Interface and Stabilization of Oil-in-Water Emulsions

Investigating the adsorption properties of emulsifiers at water-oil interfaces enables advances in the comprehension of the mechanisms governing emulsion ageing and stabilization. The utilization of natural compounds in emulsion formulations is increasingly relevant for those applications where it is challenging to maintain a low impact on the environment and health. We report here a study on saponin and chitosan at the interface between water and medium-chain triglycerides (MCT) oil in relation to the properties of the corresponding emulsions. Complementary experimental approaches have been adopted to investigate interfacial properties and emulsion evolution, relying on drop tensiometry, optical and confocal microscopy, and light transmission/scattering analysis. In addition, molecular dynamics simulation has been undertaken as support for the interpretation of the experimental results. The multi-technique investigation adopted here enabled a better understanding of saponin adsorption properties and of the role of chitosan in emulsion evolution. In particular, the results evidence the formation of amphiphilic saponin-chitosan complexes, which adsorb at the liquid-liquid interface and improve the stability of oil-in-water emulsions. Since the system investigated mainly consists of natural compounds, the results of this work can contribute to the development of new and efficient low-impact formulations.