Preparation of spherulites from jet cooked mixtures of high amylose starch and fatty acids. Effect of preparative conditions on spherulite morphology and yield

When high amylose cornstarch (amylose content: 70%) was jet cooked with 5% palmitic acid, based on amylose, spherulite yields of approximately 60%, based on total starch, were obtained. Spherulites were characterized by SEM and X-ray diffraction. The types of spherulites formed depended on the method used to cool the hot, jet cooked dispersions. Slow cooling for 22 h with magnetic stirring produced mixtures of torus/disc and spherical/lobed spherulites along with trace amounts of micron and sub-micron sized particles. In the absence of stirring, higher yields of sub-micron particles were observed along with spherulite aggregates that were comprised primarily of large, torus/disc spherulites with only minor amounts of spherical/lobed material. When jet cooked dispersions were rapidly cooled in ice, sub-micron spherical particles were the only particles observed. When defatted high amylose cornstarch was used, it was necessary to add an additional amount of palmitic acid to replace the native lipid removed from the starch sample in order to maximize yields and to avoid gel formation. Amounts of complexed palmitic acid in these spherulites varied from 4.5% to 6.1%, by weight. High yields of spherulites were also obtained when oleic acid was used; and, as observed with palmitic acid, sub-micron spherical particles were the only particles observed when the dispersion was rapidly cooled. Factors that affect the formation and morphology of these spherulites were considered.