Effect of the viscoelastic properties of modified starch as a wall material on the surface morphology of microcapsules.

ABSTRACT

BACKGROUND: Since microcapsule technology has a good protective effect on unstable bioactive substances, many studies have focused on exploring the best technical conditions for forming microcapsules. Modified starch is a microcapsule wall material with good emulsifying and film-forming properties. The objective of this work was to study the creep-recovery behavior of modified starch pastes for various creep time, shear stress and temperature. Furthermore, the effect of creep-recovery behavior on the morphology of microcapsules made of the modified starch was investigated. RESULTS: The maximum creep compliance (Jmax ), instantaneous compliance (J0 ) and retardation compliance (J1 ) of modified starch increased proportionally with increasing creep time and shear stress but decreased with increasing temperature. The Newtonian viscosity (η0 ) increased with increasing creep time and temperature but decreased with increasing shear stress. The recovery rate of the modified starch pastes varied from 0.92 to 33.68% in the creep-recovery test conditions. Creep-recovery data could be well explained by a four-parameter Burgers model (R2 > 0.918). CONCLUSIONS: Modified starch pastes exhibited time-, stress- and temperature-dependent creep-recovery behavior. The Jmax values of modified starch pastes were low(<0.20 Pa-1 ) and the η0 values high (>3.5 × 103  Pa s) for all test conditions. The results revealed the modified starch pastes had a good rigid network structure to resist deformation but recovery was difficult once deformation occurred. Microcapsules produced using the modified starch exhibited a small deformation with regular spheres and some dents, consistent with the results of creep-recovery tests. © 2019 Society of Chemical Industry.