Lamellar structure changes in rice starch during α-amylase hydrolysis: Effect of starch granule surface and channel proteins

Starch granule surface and channel proteins (GSCP) or starch granule channel proteins (GCP) were respectively removed from waxy and non-waxy rice starches . The effects of α-amylase hydrolysis on the lamellar structure changes of rice starches were examined by small-angle X-ray scattering (SAXS). SAXS revealed that the scattering peaks of hydrolyzed starch granules were broadened. The result was also evidenced by the decreased peak areas ( A ) and increased peak width at half-maximum ( W ). The α-amylase hydrolysis of starches could induce a transformation from a mass to a surface fractal and increase the compactness of starches. Moreover, the thickness of amorphous lamellae ( d a ) decreased and that of crystalline lamellae ( d c ) increased for starches after hydrolysis. Hydrolyzed starches exhibited a higher proportion of short-branch chains (fa) and long-branch chains (fb3) compared to their native form, indicating that α-amylase mainly attacked the long molecular chain of amylopectin with branch points in the amorphous lamellae. Removal of GSCP accelerated and exacerbated the decrease in d a and the increase in d c . Further, GSCP removal brought on the formation of less compact starch during long-time hydrolysis. Overall, the results demonstrated that GSCP removal had significant impacts on structural changes during α-amylase hydrolysis from lamellar to molecular scales.