Granule structural changes in native Chinese Yam (Dioscorea opposita Thunb var. Anguo) starch during acid hydrolysis

Starch extracted from Chinese Yam (Dioscorea opposita Thunb var. Angao) was treated with 2.2 mol/L hydrochloric acid for different lengths of time, (2, 4, 8, 16, and 32 days). The recovery yield, morphological, crystalline, and particle size distribution properties were investigated by scanning electron microscope (SEM), wide angle X-ray powder diffractometer (WAXRD), and laser light scattering particle size analysis (LLSPSA). The recovery yield decreased gradually with increasing hydrolysis time. The average particle size of the starch reduced continuously following acid thinning. The particle shape of the acid-thinned starch also changed significantly with acid hydrolysis. The most notable phenomenon was the conversion of thick starch granules (oval or spherical) to thin starch granules (caky or sheet). After acid hydrolysis for 32 days, most of the starch granules had disintegrated with many fragments visible. The crystalline type of the D. AG starch changed from C-type to A-type after 8 days of acid hydrolysis. This result was first found in the present study. The crystallinity level increased with increasing hydrolysis time.