Dynamic rheological and thermal properties of acetylated sweet potato starch

Dynamic rheological and thermal properties of acetylated sweet potato starch (SPS) pastes (5%, w/w) were evaluated as a function of the degree of substitution (DS). The transition temperatures (T_o, T_p and T_c) and enthalpy of gelatinization (ΔH) of acetylated SPS, which were determined using differential scanning calorimetry, were lower than those of native starch, and significantly decreased with an increase in DS. Magnitudes of storage modulus (G′), loss modulus (G″) and complex viscosity (η*) of acetylated SPS pastes were determined using a small-deformation oscillatory rheometer. Dynamic moduli (G′, G″ and η*) values of acetylated SPS pastes except for 0.123 DS were higher than those of native starch, and they also decreased with an increase in DS. The tan δ(ratio of G″/G′) values (0.37-0.39) of acetylated SPS samples were lower than that (0.44) of native starch and no significant differences were found among acetylated SPS samples, indicating at the elastic properties of SPS pastes were affected by acetylation but did not depend on DS. The G′ values of acetylated SPS during aging at 4°C for 10 h were much lower than those of native starch, showing that the addition of acetyl groups produced a pronounced effect on the retrogradation properties of SPS.