Maltodextrin-anionic surfactant interactions: isothermal titration calorimetry and surface tension study

Interactions between maltodextrin (DE = 10) and an anionic surfactant (sodium dodecyl sulfate, SDS) were studied in a buffer solution (pH 7.0, 10 mM NaCl, 20 mM Trizma, 30.0 degrees C) using isothermal titration calorimetry (ITC), surface tension, differential scanning calorimetry (DSC), and turbidity techniques. ITC measurements indicated that the binding of SDS to maltodextrin was exothermic and that, on average, one SDS monomer bound per 24 glucose units of maltodextrin at saturation. Surface tension measurements indicated that there was a critical surfactant concentration ( approximately 0.05 mM SDS) below which surfactant and maltodextrin did not interact and that the amount of surfactant bound to the maltodextrin above this concentration increased with increasing maltodextrin concentration. Turbidity measurements indicated that the solutions remained transparent at all maltodextrin (0-1 wt %) and SDS (0-20 mM) concentrations studied, which suggested that phase separation did not occur. DSC measurements indicated that no phase transitions occurred between 10 and 110 degrees C for maltodextrin solutions (0.5 wt %) in the presence or absence of surfactant. A phase diagram was developed to describe the interactions between SDS and maltodextrin.