In vitro mammalian intestine mucosal enzymatic digestion of starch spherulites formed from debranched waxy maize and high-amylose maize starches.

Starch spherulites, which are radially crystalline aggregates formed from debranched starch, have recently emerged as a unique form of resistant starch. However, their susceptibility to enzymatic hydrolysis by mammalian mucosal enzymes, the key starch-digesting enzymes in the human small intestine, remains poorly understood. This study aimed to investigate the digestibility and structural changes of starch spherulites during in vitro hydrolysis by mammalian mucosal enzymes. Four types of B-type crystalline spherulites were prepared from debranched waxy maize starch (WMS) and high-amylose maize starch (HAMS), varying in birefringence type (positive or negative). After 24 h of hydrolysis, the order of hydrolyzed starch was WMS/- (68.8%) > HAMS/- (61.9%) > WMS/+ (35.7%) > HAMS/+ (31.8%). Negative birefringent spherulites, which had more surface cracks and larger enzyme-accessible areas, exhibited higher enzyme binding and faster hydrolysis. In contrast, HAMS/+ spherulites exhibited the highest resistance to digestion, showing minimal morphological changes and retention of birefringence. Even though HAMS/- had higher crystallinity and melting enthalpy than WMS/+, it was more digestible due to its cracked surface. These findings suggest that enzyme resistance of starch spherulites is determined not only by crystallinity and chain length, but also by birefringent sign (molecular assembly), aggregation behavior, and surface morphology.