Electrical conductivity of stevia rebaudiana-surfactant mixture aqueous solution: Roles of temperature and sugar substitute concentration

The investigation of stevia-surfactant systems is of significant importance for the extraction process of steviol molecules as well as for the formulation of food products. The present study investigates the electrical conductivity of aqueous solutions containing a sugar substitute and surfactant over a temperature range of 25–50 °C. The sugar-substitute, Stevia Rebaudiana, concentration Cs (g/mL), is ranged from 0.047 to 0.6. The surfactant, Sodium bis(2-ethylhexyl) sulfosuccinate (AOT), has a concentration range of 1.4 ≤CAOT (g/L)≤ 6. The degree of ionization in ionic micelles, α, is determined by examining the conductivity of AOT in Stevia-free water, where complete micelle dissociation is observed. In the presence of Stevia Rebaudiana, a significant exponential decay in system conductivity with respect to the concentration of the sugar substitute is observed. Empirical equations were introduced to describe this behavior. The temperature dependence of conductivity is modeled using an Arrhenius equation. We postulate the formation of pseudo-micelles arising from interactions between the sugar substitute and surfactant, characterized by an effective degree of ionization in ionic micelles, αe.