Effect of Acetylation on Rheological Properties of Rice Starch

Rheological properties of acetylated rice starch pastes (5%, w/w) as a function of acetyl degree of substitution (0.025–0.104) were evaluated in steady and dynamic shear. The acetylated rice starch pastes at 25°C had high shear‐thinning behavior ( n = 0.17–0.20) with high Casson yield stress (σ oc = 47.4–84.1 Pa). Magnitudes of consistency index ( K ) and yield stress (σ oc ) increased with increase in acetyl substitution degree. Apparent viscosity (η a,100 ) obeyed the Arrhenius temperature relationship over the temperature range of 10–55°C; the activation energy ( E a ) values of acetylated starch pastes were in the range of 9.46–11.4 kJ/mol. Magnitudes of storage modulus ( G ′), loss modulus ( G ′′) and complex viscosity (η*) of acetylated starch pastes increased with increase in degree of acetyl substitution, and the magnitudes of G ′ were also much greater than those of G ′′ and η* at all values of frequencies (ω). The Cox‐Merz superposition rule did not describe the relationship between dynamic (η*) and apparent viscosity (η a ) for all samples.