Structure, physicochemical properties and in vitro digestibility of extruded starch-lauric acid complexes with different amylose contents

Starch-lipid complexes, which are types of resistant starch (RS), formed readily using extrusion processing in the industrial setting, but their formation is mainly affected by the amylose content of the starch. The aim of this study was to investigate the effects of the amylose content and lauric acid (LA) content on the crystallinity, thermal properties, functional properties, and in vitro digestibility of extruded starch-lipid complexes. Potato starch, corn starch, and pea starch with different amylose contents were used to form extruded starch-lipid complexes with a range of lauric acid (LA) content (1%, 2% and 4%). The extruded potato starch (EPS), extruded corn starch (ECS), and extruded pea starch (EPES) all formed stable and resistant form II complexes with LA during extrusion. The V-type crystal structure of the complexes became more obvious as the LA content increased from 1% to 4%. The dissociation temperature of complexes ranged from 110 to 130 °C, and the enthalpy change increased with increasing LA content. Moreover, the complexes rapidly reformed after dissociation and cooling. The solubility and swelling power of the complexes decreased with increasing LA content. The peak viscosity of the complexes was significantly reduced compared with extruded starch, consistent with the reduced swelling power. The RS content of the complexes was closely related to both the amylose and the LA contents. The RS contents of the EPS-LA, ECS-LA, and EPES-LA complexes with 4% LA content were 10.0%, 14.5%, and 16.7%, respectively. These findings provide a theoretical foundation and practical guidance for industrial production of starch-lipid complexes for efficient reduction of starch digestibility.