Linear and nonlinear rheological behavior of native and debranched waxy rice starch gels

The rheological behaviours of native (WX) and debranched (DB) waxy rice starch gels in the linear viscoelastic (LVE) regime and non-linear (NL) regime were investigated using small amplitude oscillatory shear (SAOS), and large amplitude oscillatory shear (LAOS), respectively. Our results show that WX starch gels exhibited a wider LVE region than DB starch gels, and a scaling of G' with frequency given by G'similar to omega(0.26). The G and G '' scaled nearly linear with concentration and were nearly independent of temperature in the tested range. The Lissajous plots showed a gradual yielding of the gels, followed by softening behavior. These results indicated that the WX gel has the characteristics of a weak particle gel (of non-entangled polymers). In contrast, the DB starch produced gels with a more stiff and brittle behavior. The shear moduli had a very strong concentration dependence (similar to C-10.30) and temperature dependence. The DB starch gel showed more abrupt yielding and strong softening behavior in the Lissajous curves. Creep measurements showed a lower compliance for these gels, and significant creep ringing. These observations suggest the DB starch gels consist of clusters of stiff polymers.