Microstructure, thermodynamics and rheological properties of different types of red adzuki bean starch

Starches were isolated from three cultivars of red adzuki beans, including Da Hongpao (DHP), Bao Qinghong (BQH) and Zhen Zhuhong (ZZH), and their morphological, structural and physicochemical properties were studied. Statistical analysis of the physicochemical and functional properties data revealed a significant (P < 0.05) difference among the three starch types. Starch of DHP cultivar showed low amylose content, smooth and round particle morphology, with obvious polarised crosses. The average particle size of the three adzuki bean types was in the range of 35.58–43.29 μm, with that of DHP being the smallest, 35.58 μm. The X-ray diffraction patterns showed that all the starches were type A with reflections (2θ) at 15.0°, 17.03° and 23.3°. The bands of Fourier transforms infrared spectra of the three starches revealed their carbohydrate properties, and the intensity of the Fourier spectral absorption band of starch from DHP was weaker than that of the other cultivars. Further, the relative crystallinity of the three starches ranged from 22.7 to 29.4%, and DHP showed the highest crystallinity of 29.4%. Additionally, starch of the DHP cultivar revealed high gelatinisation, peak viscosity and enthalpy as compared to those from the other two adzuki bean cultivars. The shear viscosity of the three starch types decreased with increasing shear rate; when the shear rate was 10 s, the shear viscosity of the DHP-derived starch significantly decreased. Moreover, both the modulus (G’) and the loss modulus (G’’) increased with increasing dynamic frequency, and the DHP-derived starch showed the lowest G’ and G’’ values. In summary, this work provides data that may help in promoting the application of starches isolated from red adzuki bean in the food industry.