Recrystallization of waxy maize starch during manufacturing of starch microspheres for drug delivery: Optimization by experimental design

Gelatinized starch/water dispersions with a water content of 70% w/w were studied in order to evaluate the influence of the incubation time at two fixed temperatures (6 and 37 °C) on the recrystallization behavior. The starch material was produced from waxy maize starch by acid hydrolysis followed by a mechanical treatment, i.e. a high pressure homogenization. Empirical models for the recrystallization of the model starch dispersions were investigated by using a central composite circumscribed (CCC) design in two factors involving 11 trials. The rebuilt crystalline structure was estimated by measuring the melting transition parameters with differential scanning calorimetry (DSC). The designed models for the melting enthalpy, the melting transition temperatures, and the melting interval as the responses were reproducible and predictable and the results were analyzed by using a response surface modeling. Operative conditions for the formation of the most thermally stable crystalline structure with the highest possible crystallinity were determined. It was also concluded that the decisive factor for the crystallinity of the given starch material was a prolonged storage at 6 °C, while thermal characteristics of the crystallites could be controlled by storage at 37 °C. An interaction effect was observed between the incubation time at these two experimental temperatures regarding enthalpy values and the melting interval of the samples.