In vitro digestion properties of heterogeneous starch granules from high-amylose rice

• High-amylose rice starch had polygonal, aggregate, elongated, and hollow granules.
• In vitro digestion properties of these heterogeneous starch granules were studied.
• Only polygonal and aggregate starches had monophasic digestograms from 0 to 8 h.
• Elongated and hollow starches were rapidly degraded in first 20 min of digestion.
• Undigested starch residues were analyzed using GPC, XRD, FTIR, and SAXS.

High-amylose rice endosperm contains polygonal, aggregate, elongated, and hollow starch granules. In this study, in vitro digestion properties of native starches and structural properties of undigested starch residues were investigated. The polygonal and aggregate starches had monophasic digestograms and the elongated and hollow starches had biphasic digestograms from 0 to 8 h of digestion, but only the digestions of polygonal and aggregate starches were well fitted by first-order kinetics. The elongated and hollow starches were rapidly degraded in first 20 min of digestion, but had high resistance to degradation after 2 h of digestion. The polygonal and aggregate starches had side-by-side digestions of amylose and amylopectin as well as crystalline and amorphous components, but amylose and amorphous component of elongated and hollow starches were rapidly degraded in first 20 min of digestion. The B-type allomorph in aggregate, elongated, and hollow C-type starches contributed to the resistance to digestion.

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