RHEOLOGICAL PROPERTIES OF CALCIUM TREATED HYDROXYPROPYL RICE STARCHES

Unisolated rice starch was used for hydroxypropylation and calcium com plexation. Viscosity was measured at different starch concentrations, temperatures, and shear rates. The viscosity decreased with increase o f calcium concentrations and shear rates. Temperature, starch concentr ations and levels of Molar Substitution (MS) enhanced the viscosity. H ysteresis behaviour was markedly influenced by levels of calcium and M S. Higher viscosity was observed in hydroxypropyl starch. It is assume d that starch. molecules exist in an expanded and/or extended forms wh ich may result in higher viscosity. Calcium treated starch shows lower viscosity. Calcium ions possibly squeezed the starch molecules into 8 tighter configuration and/or calcium may compete with starch for wate r causing the limitation of water thus resulting in reduction of visco sity. Higher viscosity was observed at higher temperatures. Higher tem perature cause the starch granules swelling thus produce higher fricti onal forces responsible for higher viscosity.