Effect of Molar Substitution (MS) on Calcium Binding by Hydroxypropyl Rice Starches

Unisolated rice starch was obtained by wet milling of broken milled rice grains. Hydroxypropyl rice starches of different level of molar substitution (MS) were prepared and characterized. Both native and modified starches were treated with calcium carbonate at various calcium: starch ratios. Binding was markedly influenced by the calcium concentration in the reaction mixtures. Native starch binds less calcium than modified starch. Ability to bind calcium decreased with increasing calcium concentration in both native and modified starches. A parallel increased in calcium binding was observed as MS increased to the value of 0.09 and thereafter reversed. Increased level of substitution depressed the optical rotation and electrical conductivity of starch‐calcium complex.