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 (da) decreased and that of crystalline lamellae (dc) 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 da and the increase in dc. 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.