Starch is a prominent component of the human,diet and is hydrolyzed by alpha-amylase post ingestion Probing the mecharnsni of this process has proven challenging, due to the intrinsic,heterogeneity of individual starch granules By means of solution-state NMR, we demonstrate that flexible polysaccharide chains protruding from the solvent exposed surfaces of waxy rice starch granules are highly mobile and that during hydrothermal-treatment, when the granules swell; the number of flexible residues on the exposed surfaces ineteases by a factor of 15. Moreover, we show that these flexible chains are the primary substrates for a-amylase, being cleaved in the initial stages of hydrolysis. These findings allow us to conclude that the quantity of flexible a-glucan chains protruding from the granule surface will greatly influence the rate of energy acquisition from digestion of starch.