Granule structure of C-type Chinese Yam (Dioscorea opposita Thunb var. Zhongbowen) starch by acid hydrolysis

Granule structure of C-type starch separated from Dioscorea opposita Thunb var. Zhongbowen (D. ZBW) was characterized by scanning electron microscope (SEM), X-ray powder diffractometer (XRD) and laser light scattering particle size analyzer (LLSPSA) in the process of acid hydrolysis. D. ZBW starch was treated with 2.2 mol/l hydrochloric acid for different lengths of time. The SEM results revealed that the amorphous regions of the starch located at the centre of the granules while the outer layer of the granules was mainly composed of the crystalline areas. The crystal type of the starch changed from typical C-type X-ray diffraction pattern to the representative A-type pattern in the process of acid hydrolysis by XRD analysis. The above results demonstrated that B-type polymorphs present in C-type starch granule was preferentially degraded at the first stage of hydrolysis followed by A-type polymorphs. The acid-thinned starch granules displayed a gradual reduction in the particle diameter followed the acid thinning.