Nanofiltered saponin-rich extract of Saponaria officinalis – adsorption and aggregation properties of particular fractions

Plant extracts containing saponins combine high emulsifying properties with antibacterial activity, which makes them valuable adjuvants in pharmaceutical and food products. Saponins are natural surfactants present in various plant species, including Saponaria officinalis. Due to the variety of chemical structures and diversity of saponins in plant extracts, their surface-active properties are complex and differ from those of chemically pure surfactants. Hence, the aim of the study was to determine the correlation between the composition of S. officinalis extracts and their surface properties. The first stage of the study was characterization of the composition of the extracts studied by liquid chromatography coupled with mass spectrometry. Then the surface tension of the aqueous solutions of these extracts was measured, which permitted determination of their adsorption and aggregation parameters. The results have pointed out the differences between the properties of the studied extracts and those of pure surfactants of known molecular structure. The constants in the Szyszkowski equation allowed determination of the maximal excess concentration of a given extract at the water-air interface and the value of the Gibbs free energy of adsorption. The mentioned parameters were also determined from the Gibbs adsorption isotherm equation and the Langmuir equation modified by de Boer. The results obtained by these methods were found to be comparable with those determined from the Szyszkowski equation. What is more, it was found that the adsorption parameters correlated with the micelle sizes formed by the components of the tested S. officinalis extracts. All these valuable data help devise the informed use of extracts containing saponins in many branches of science and economy.