Micellar Properties of Quillaja Saponin. 1. Effects of Temperature, Salt, and pH on Solution Properties

We used surface tension and dye solubilization measurements to demonstrate that quillaja saponin molecules aggregate into micelles above a critical micelle concentration (cmc), whose value ranges between 0.5 and 0.8 g/L at 298 K. Below the cmc, this surfactant forms a saturated interfacial layer with 2 μmol/m2. Increased temperature or pH increases the cmc, while increased salt concentration decreases this value. The size of saponin micelles was found to increase strongly with temperature but to have little dependence on salt concentration or pH. The effect of increased temperature on size is accompanied by a decrease in intrinsic viscosity, suggesting substantial dehydration of the micelles at higher temperatures. We also observed some differences between quillaja saponins obtained from various commercial sources. The knowledge gained from these studies of quillaja saponin solutions is useful in exploring their ability to extract solutes of biological significance and for understanding the functioning of these biological surfactants in foods and in vivo. Keywords: Micelles; critical micelle concentration; aggregation number; solubilization