Molecular rearrangement of waxy and normal maize starch granules during in vitro digestion

• Neither the A- nor B-type crystallinity was resistant to enzyme hydrolysis.
• Linear dextrins retrograded into thermally stable crystallites during digestion.
• Different mechanisms of slow digestibility were observed from two B-type starches.
• Stable crystallites contributed to slow digestibility of high-amylose maize starch.
• Slow digestibility of normal potato starch was due to its granular structure.

The objective of the present study is to understand the changes in starch structures during digestion and the structures contributing to slow digestion properties. The molecular, crystalline, and granular structures of native waxy maize, normal maize, high-amylose maize, and normal potato starch granules were monitored using SEC, XRD, DSC, and SEM. The amylose and amylopectin molecules of all four starches were hydrolyzed to smaller dextrins, with some having linear molecular structure. Neither the A- nor B-type crystallinity was resistant to enzyme hydrolysis. Starch crystallites with melting temperature above 120 °C appeared in waxy and normal maize starches after digestion, suggesting that the linear dextrins retrograded into thermally stable crystalline structure. These crystallites were also observed for high-amylose maize starch before and after digestion, contributing to its low enzyme digestibility. On the contrary, the enzyme-resistant granular structure of native normal potato starch was responsible for its low susceptibility to enzyme hydrolysis.