Surface regions of untreated and heat–moisture treated (HMT) normal rice, waxy rice, normal corn, waxy corn, normal potato, and waxy potato starch granules were examined by atomic force microscopy (AFM). AFM images revealed surface roughness of untreated starch granules and protrusions with a diameter of approximately 15–90 nm. After treatment, the smooth surface region on starch granules was observed, especially in normal rice, waxy rice, and normal corn starches. A significant reduction in the size of protrusions on the surface of HMT potato starch granules was also detected. The newly formed structures may act as barriers and retard water penetration into starch granules. The blocklet model of starch granule architecture was also confirmed by the AFM images.
Heat–moisture treatment; Atomic force microscopy; Nano-structure; Normal starch; Waxy starch