Rheological properties of agar microgel suspensions prepared using water-in-oil emulsions

Agar microgel suspensions containing sugar fatty acid esters were prepared using a water-in-oil (w/o) emulsion system. The volume fraction of microgel particles was adjusted by centrifugation to obtain high volume fraction suspensions. The relationship between the apparent equilibrium shear modulus and the volume fraction was analyzed using a hard-sphere model. The rigidity of the microgel particles never affected the rheological property under the random close-packed-volume fraction, but it affected the fracture of the structure composed of packed microgel particles. The length of fatty acid emulsifiers also affected the rheological properties of the condensed suspensions. The stress growth under step shear flow was observed to study the lubrication effect of close-packed microgel particles containing ER-190 (C 22:1) or O-170 (C 18:1). Although both suspensions showed strain softening, the tendency was different in each. Such a w/o microgel suspension is a likely candidate for use in low-fat foods. © 2011 Japanese Society of Biorheology.