Comparison of structural characteristics and <i>in vitro</i> digestibility of <i>Canna edulis</i> resistant starch produced by autoclaving and heat-moisture treatment

Resistant starch (RS) has attracted considerable attention due to its ability to modulate postprandial glycaemic response and its relevance to glycaemic control.RS type RS3 from Canna edulis Ker was prepared using two physical modification methods, namely autoclaving-retrogradation (Ar) and heat-moisture treatment (HMT), which were combined with dual enzymatic hydrolysis (α-amylase and amyloglucosidase) to obtain the Ar-Hydro and HMT-Hydro samples.The starch samples were evaluated with respect to their structural characteristics, physicochemical properties, and in vitro digestibility.The results showed that the combined treatments caused substantial disruption of starch granules, leading to roughened surfaces and irregular morphologies.The apparent amylose content varied significantly, with the lowest value observed in Ar (30.45%) and the highest in Ar-Hydro (39.35%).Relative crystallinity decreased in the following order: Ar-Hydro (34.09%) > HMT-Hydro (32.15%) > Ar (30.68%) > HMT (28.41%).In vitro digestion analysis revealed that Ar-Hydro exhibited the lowest hydrolysis index and estimated glycaemic index (GI), which were associated with reduced swelling power and water absorption capacity, as well as well-organised double-helical structures and higher crystallinity.Compared with the single thermal treatments, the combined AR and dual enzymatic hydrolysis process increased the RS content and markedly reduced the estimated GI.This study elucidated the role of short linear glucans generated during enzymatic hydrolysis in the rearrangement and stabilisation of crystalline structures, thereby enhancing the digestion resistance of canna starch and providing insight into the structure-digestibility relationship.These findings highlight the potential application of modified canna starch in the development of functional foods for glycaemic control.