Effect of starch fractions on spherulite formation and microstructure

The effect of amylose, amylopectin, and intermediate material on starch spherulite formation and microstructure was investigated. Spherulites were observed in all samples made from high amylose maize starch fractions, but could not be observed when common corn or potato amylopectin were used. More numerous and better developed spherulites were formed with higher proportions of amylose. The dissolution temperature of spherulites made from common corn and potato starch amylose was 123–124 °C and 110–111 °C, respectively. However, the dissolution temperature of spherulites made from high amylose maize starch fractions decreased with higher proportions of branched material, ranging from 93 °C to 116 °C. SEM, TEM, and AFM images showed that starch spherulites may develop from a sheaf-like precursor, have an internal radial organization, and a blocklet nanostructure similar to some synthetic spherulites. This study shows that spherulitic crystallization of starch is favored by a higher ratio of linear to branched material.