The partial characterization of C-type rhizoma Dioscorea starch granule during acid hydrolysis

D. BY (Dioscorea opposita Thunb. cv. Baiyu ) starch was treated with 2.2 mol/L hydrochloric acid for different lengths of time: 2, 4, 8, 16, and 32 days. The starch yield, morphological, crystalline and particle size distribution properties were characterized by scanning electron microscope (SEM), X-ray powder diffractometer and light scattering particle size analyzer (LSPSA). The starch recovery yield decreased gradually with the hydrolysis time increasing. The SEM results showed that the inner structure of the starch granules was preferentially hydrolyzed, then the outer part. After acid hydrolysis for 16 days, the morphology of D. BY starch changed greatly, most of the starch granules have been disintegrated into smaller fragments. The crystalline type of the D. BY starch changed from C-type to A-type after 16 days of acid hydrolysis. This was firstly found in the present study. This result indicated that the B-type polymorph in the C-type D. BY starch was firstly attacked by hydrogen ion and then the A-type polymorph. The crystallinity level increased with an increase in the hydrolysis time. In addition, the particle diameter of D. BY starch decreased from 26.8 to 18.2 μm with an increase in the hydrolysis time.