Characterization of physicochemical and digestive properties of starches from various "dainagon" adzuki beans (Vigna angularis) cultivated in Japan.

We investigated the physicochemical properties of starches extracted from Vigna angularis variants Noto-dainagon, Kyoto-dainagon, dainagon, and erimo-type adzuki beans. The particle size was larger in the Noto-dainagon starch than in the other starches, but all starches displayed a C-type crystal structure in the X-ray diffraction analysis. The onset and peak temperatures of gelatinization were approximately 7 °C lower in the Noto-dainagon and Kyoto-dainagon starches than in the dainagon and adzuki bean starches. The dainagon and adzuki bean starches also demonstrated lower swelling power at 60 °C than the other starches. The rapid visco-analyser curves of all starches showed no breakdown during the heating process, and the final viscosities of the starches increased with decreasing temperature. The apparent amylose and phosphorus contents were highest in the Noto-dainagon starch (36.6% and 95.6 ppm, respectively). The branched- chain length degree of polymerization 6-12 was lowest in the adzuki bean starch. In vitro and in vivo analyses of the digestive properties indicated that dainagon starch was more indigestible than the other starches. We considered that dainagon starch was a potentially viable health-promoting ingredient.