MODIFICATION OF NATURAL POLYMERS BY THERMO-MECHANICAL PROCESSING
Location: Plant Polymer Research
Title: Preparation of Spherulites from Jet Cooked Mixtures of High Amylose Starch and Fatty Acids. Effect of Preparation Conditions on Spherulite Morphology and Yield
Submitted to: Carbohydrate Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 24, 2007
Publication Date: January 24, 2008
Citation: Fanta, G.F., Felker, F.C., Shogren, R.L., Salch, J. 2008. Preparation of spherulites from jet cooked mixtures of high amylose starch and fatty acids. effect of preparation conditions on spherulite morphology and yield. Carbohydrate Polymers. 71(2):253-262.
Interpretive Summary: Crystalline particles are formed from the amylose component of cornstarch when the starch is jet cooked in the presence of a fatty acid, and the hot dispersion is allowed to cool. End-use applications of these particles depend upon their size and shape, and also upon our ability to develop a practical process for preparing the particles in high yield. In this study, we have shown that high yields of particles can be obtained by using a high amylose variety of cornstarch, and by adding enough fatty acid to form a complex with all of the amylose in the starch sample. We have also shown that the size and shape of the crystalline particles depends upon the conditions used for cooling the jet cooked dispersions. If the hot dispersions are rapidly cooled in ice, very small crystalline particles are obtained that are suitable for use in food products and as biodegradable fillers in plastics.
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 hrs 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 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.