Dynamic rheological and physicochemical properties of annealed starches from two cultivars of cassava

Starch from tubers of “sweet” (low cyanide) and “bitter” (high cyanide) cassava (Manihot esculentum Crantz) crops was isolated and subjected to annealing treatment at 50 °C for 24,96,144 and 192 h in 1:5 starch to water ratio. Annealing generally reduced the swelling power and solubility of the starches. Storage modulus (G′) and loss modulus (G″) increased with decrease in complex viscosity (Eta*) as a function of angular frequency (ω). The magnitudes of G′ reported were greater than those of G″ revealing frequency dependency except sweet starch cultivar annealed at 192 h. The tan δ (ratio of G″/G′) of annealed starches were within the ranges of 0.31–0.39 and 0.23–0.45 for sweet and bitter cultivars, respectively. The tan δ values of the starches were lower than one, indicating that the samples are elastic in nature than viscous. The X-ray patterns of the A-type starches were not altered on annealing denoting that the double helices in the amorphous region were not disrupted. Annealing as revealed by scanning electron micrographs changed the structure of the sweet cultivar, while there was no change in the size and shape of the bitter cultivar.