Formation and crystalline structure of spherulites from pea and high amylose maize starches

Starch spherulite is a unique form of resistant starch characterized by a spherical structure with crystalline lamellae that are radially oriented and may find applications in delivery of nutrients and bioactives to the lower gastrointestinal tract. Formation of starch spherulites generally requires heating to a high temperature followed by quenching and long crystallization time. The objectives of this study were to gain a deeper understanding of the factors influencing spherulite formation from pea starch (PS) and high-amylose maize starch (HAMS) and investigate if spherulites could be formed by a slow cooling rate and determine the crystalline structure and morphology of the spherulites formed. Remarkably, spherulite was observed immediately after PS and HAMS (25 % solids) were heated to 180 °C and cooled to 10 °C at a cooling rate of 10 °C/min in a differential scanning calorimeter (DSC) pan. Increasing heating temperature degraded starches more but improved the morphological quality of spherulites. Spherulite was better formed at 25 % solids content than 40 %. Both PS and HAMS formed spherulites with a predominant B-type crystalline pattern with 13-17 % crystallinity at ca. 10 % moisture content. PS displayed a single exothermic peak on cooling due to spherulite formation (recrystallization), whereas HAMS exhibited an extra peak due to the amylose-lipid complex formation. Spherulite production from HAMS and PS was successfully scaled up using a pressure reactor. This study provides a simplified approach for spherulite production, new potential utilization of PS and HAMS, and valuable insights for optimizing formation of starch spherulites.