Physicochemical and structural properties of low-amylose Chinese yam (Dioscorea opposita Thunb.) starches

Abstract

Nuoshanyao (NSY), Tiegunshanyao (TSY) and Huaishanyao (HSY) are the main cultivars of Chinese yam (Dioscorea opposita Thunb.) widely grown in China. The composition, physicochemical properties, morphology, and thermal properties of the starches from these cultivars were investigated in this study. NSY starch (17.0%) was much lower in amylose content than other cultivars (33.4-34.5%). The average particle diameter of the starches ranged from 25.83 to 28.93 μm. Weight-average molecular weights (Mw) and number-average molecular weights (Mn) ranged from 1.29 to 1.84 × 10⁵ g/mol and 5.93 to 8.36 × 10⁴ g/mol, respectively. NSY starch had higher gelatinization temperature (71.5 °C), enthalpy (14.14 J/g), peak viscosity (8590 cP) and swelling power (12.0%) than TSY and HSY. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) tests indicated that Chinese yam starches had CB-type crystalline structure with crystallinity ranging from 21.91% to 27.08% and a short-range ordered structure. T_o, T_p, ΔH, peak viscosity and swelling power at 95 °C were significantly correlated to amylose content. The low-amylose NSY starch was found to have high gelatinization temperature, enthalpy, peak viscosity and swelling power. These specific physicochemical and structural properties indicated the industrial potential of low-amylose yam starch.

Keywords: Physicochemical properties; Structural properties; Yam starch.