Effect of saponins from quinoa on a skin-mimetic lipid monolayer containing cholesterol

The study discusses the effect of a quinoa seed coat extract on a cholesterol-based Langmuir monolayer mimicking the intercellular lipid mixture in the skin's outermost layer - stratum corneum. Besides cholesterol (CHOL), the monolayer contains also stearic acid (SA) and ceramide VI (CER), in a molar ratio of 10:14:14. Three quinoa extracts were tested for their surface activity: a) from the whole seed, b) from the dehulled seed, and c) from the seed coat. The latter shows significantly higher ability to reduce surface tension (increase surface pressure) than the others. Its adsorbed layers display also reasonable surface dilational elasticity (storage) modulus, E'. These observations are in line with the literature reports on the high concentrations of triterpenoid glycosidic biosurfactants - saponins, in quinoa seed, especially in its coat. The saponin-rich extract of quinoa seed coat was thus introduced underneath the pre-formed lipid monolayer compressed to surface pressure, Π = 30 mN/m in a Langmuir trough, in order to register the surface pressure response. The increase of both the surface pressure and surface dilational elasticity modulus suggests that saponins, and possibly other surface-active components of the extract, incorporate into the model lipid monolayer, without solubilizing it. This opens new perspectives for the saponin-rich quinoa seed extract as skin penetration-enhancing active components for cosmetics or pharmaceutical purposes.