Pasting and rheological properties of oat starch and its derivatives

Modification of starch led to new product with new desirable properties. Oat starch was subjected to different chemical modifications (acetylation, oxidation and phosphorylation). These processes greatly influenced physico-chemical properties of starch. There were observed shifts in molecular mass, as well as in amylose, lipid and phosphorus content. Also some changes were observed in gelatinization characteristics of starches, the most visible in case of acetylated starch. Introduction of functional groups greatly increased such starch properties, in comparison to native one, like water binding capacity (WBC) and aqueous solubility (AS). Also the influence of chemical modifications on rheological properties of oat starch pastes were investigated. Pasting characteristics of 5.00% starch suspensions were performed. For acetylated and starch phosphate pasting curves had a similar course. The other group of pasting curves was created by viscosity profiles obtained for oxidized and native starches. Rheological properties of 4.00%, w/w starch pastes were evaluated based on flow curves and results of equilibrium tests. Power law rheological models were fitted to the obtained data. All pastes were classified as shear thickened fluids. Flow index values were practically temperature independent, with exception for native starch paste. Yield stress values were calculated for pastes at 20 °C, but were impossible to determine for acetylated starch due to sample gelling. Rheological properties of starch pastes and pasting characteristics were compared. The viscosity oscillations of native and oat starch phosphate pastes were observed. Possible reasons of thixotropy behavior occurrence at 20 °C, and its vanishing at 50 °C were discussed.