Structural and Functional Characteristics of Chinese Dioscorea Esculenta and Dioscorea Opposita Starches

Physicochemical, structural, and functional characteristics of starch from Dioscorea esculenta was compared with that from Dioscorea opposita Thunb. The scanning electron microscopy results showed that starches from D. esculenta and D. opposita differed in morphological features and distribution of granule size. While the D. esculenta starch possessed irregular, polygonal shape with the particle size distribution in the range of 1.7–4.2 μm, the D. opposita starch displayed large, oval and smooth shape with the particle size distribution in the range of 15.4–39.5 μm. The D. esculenta starch displayed a B-form diffraction pattern with 36.8% of crystalline degree, while the D. opposita starch exhibited a C-form crystalline pattern with 26.5% of crystalline degree. The amylose contents were also different for D. esculenta starch (18.15%) and D. opposita starch (22.43%). The gelatinization temperature (peak temperature) of D. esculenta starch (76.34°C) was lower than that of D. opposita starch (79.81°C). The pasting initial temperature (Ti), maximum viscosity, breakdown viscosity, and setback viscosity of D. esculenta starch were 68.7°C, 359 BU, 0 BU, and 262 BU, respectively. Interestingly, the amounts of readily digestible and slowly digestible starch contents in D. esculenta starch were higher, whereas its resistant starch contents were lower than those of D. opposita starch.