Isothermal titration calorimetry study of the influence of temperature, pH and salt on maltodextrin–anionic surfactant interactions

Abstract

The effects of temperature (10–50 °C), pH (3–7) and salt concentration (0–100 mM NaCl) on the interactions between maltodextrin (DE=5) and an anionic surfactant (sodium dodecyl sulfate, SDS) were studied using isothermal titration calorimetry (ITC). ITC measurements indicated that the enthalpy changes associated with surfactant demicellization were highly temperature dependent, going from endothermic at higher temperatures to exothermic at lower temperatures. In contrast, the enthalpy changes associated with binding of surfactants to maltodextrin were always exothermic and much less sensitive to temperature. A minimum was observed for both the critical micelle concentration (CMC) of SDS and the apparent CMC (CMC*) of SDS in the presence of maltodextrin at intermediate temperatures (∼30 °C); however, the temperature dependences of the CMC and CMC* were quite small (∼0.5 mM). There was no effect of pH (3, 5, and 7) on surfactant demicellization or binding to maltodextrin. On the other hand, salt concentration (0, 10, and 100 mM NaCl) affected both of these parameters: there being a decrease of CMC and CMC* with increasing salt concentration and a maximum in the amount of surfactant bound to maltodextrin at 10 mM NaCl.