Preparation and properties of starch phosphates using waxy, common, and high-amylose corn starches. II. Reactive extrusion method

The structure and physicochemical properties of extruded waxy, common, and high-amylose corn starch phosphates prepared using slurry and dry-mixing treatments were studied. Extrusion parameters including moisture content and zone temperatures were optimized. All phosphorylated starches showed improved freeze-thaw stability, decreased retrogradation, and improved water binding relative to their parent starches. The extrusion process greatly increased the degree of phosphorylation compared with the conventional oven-heating method. The extrusion parameters of high pressure, temperature, and shear enhanced the efficiency of phosphorus incorporation. The slurry treatment was more effective than dry mixing in incorporating phosphate groups because its higher moisture content allowed for better mixing under the reaction conditions studied. The phosphorylated starches prepared by the slurry treatment exhibited a lower gelatinization temperature and enthalpy, a higher pasting viscosity profile, and improved swelling and freeze-thaw stability compared with those prepared by the dry-mixing treatment. The amount and location of phosphorus incorporated into starches by extrusion varied with starch composition and sample treatment before extrusion. Waxy starch was more prone to phosphorylation, followed by common and high-amylose starches, respectively.