Changes in physico-chemical and rheological properties of rice during flaking

Hydration, solubility, pasting and rheological properties of roasted-parboi led rice and flakes were examined in comparison to raw rice. There was an i ncrease in the hydration capacity, swelling power and solubility during roa sting-parboiling of rice as a result of gelatinization of its starch. Flaki ng caused further increase due to damage of starch by application of mechan ical force. The changes were higher in flakes from roller-flaker as compare d to those from edge-runner. Pasting characteristics of flour slurries in R apid Visco Analyzer showed a typical profile for pregelatinized products vi z. a higher initial viscosity but a lower peak viscosity for roasted-parboi led rice and flaked rice than for raw rice. The viscosity curves and flow c urves of the products over a wide range of shear rate indicated a non-Newto nian, pseudoplastic behaviour for all the samples. All samples showed typic al hysteresis loop in their viscosity curves indicating their thixotropic n ature. Flakes from roller-flaker exhibited lower viscosity but more thixotr ophy indicating higher starch breakdown in them than in edge-runner flakes, which seemed to have more of heat damaged starch.