Synergistic effect of sodium dodecyl sulfate and salts on the gelation properties of acid-hydrolyzed-hydroxypropylated potato starch

Appropriate modifications of starch are necessary to meet the industrial demand for high-quality hard capsule materials as an alternative to gelatin. In the present study, the influence of sodium dodecyl sulfate (SDS) and salts on the gelation properties of acid-hydrolyzed-hydroxypropylated potato starch (AHP) was characterized using dynamic rheological tests. A significant phenomenon was discovered in terms of a synergistic effect between SDS and salts, and was further explored using blue-value and zeta-potential analyses. In particular, the gelation temperature of the AHP pastes increased with increasing concentrations of KC1 until there was not enough SDS available to achieve a cooperative effect. Formation of a starch-SDS inclusion complex led to a weakened combination of starch-iodine, and increased the surface charge of starch molecules. Moreover, a decrease in zeta-potential value was observed along with the addition of KC1. Considering the charged sulfate groups of complex starch-SDS, which was provided by SDS, were similar to that of carrageenan, we put forward a hypothesis that the observed synergistic effect of SDS and salts is mainly attributed to the electronic interactions between salt ions. The current study provides a necessary strategy for applying AHP as a gelatin alternative in the manufacturing of hard capsules.