Comparison of the structural characterization and physicochemical properties of starches from seven purple sweet potato varieties cultivated in China

In this study, the structural characterization and physicochemical properties of starches from seven purple sweet potato varieties (Fuzi No. 1, Guang No. 161, Jihei No. 1, Ningzi No. 1, Ningzi No. 2, Xuzi No. 6 and Xuzi No. 8) cultivated in China were compared. Starch granules of purple sweet potatoes all exhibited round, polygonal and hemispherical shapes with granule sizes ranging from 4.3 to 23.6 μm. X-ray powder diffraction patterns and 13C nuclear magnetic resonance spectra revealed purple sweet potato starches were CA-type with relative crystallinity varying from 34.0% to 37.3%. Small-angle X-ray scattering spectra indicated the lamellar repeat distances of starch granules were in the range of 9.962-10.137 nm. Ratios of 1045/1022 cm-1 and 1022/995 cm-1 of Fourier transform infrared spectra varied in the range of 0.689-0.887 and 0.850-0.974, respectively. Amylose contents of purple sweet potato starches differed from 18.2 to 27.2%. Purple sweet potato starches exhibited different gelatinization properties but similar thermal stability. Moreover, resistant starch contents varied from 29.25% to 43.50%. Our study indicated the granule size, relative crystallinity, the degree of short-range order, amylose content, gelatinization property and in vitro digestibility of purple sweet potato starches were greatly influenced by the variety of purple sweet potato.