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Phosphorylation of starch by reactive extrusion
Starch is a type of carbohydrate, consumed within foods or added into foods after being isolated from its source. It also can be modified and then added into food products. One of the modifications of starch, cross-linking, improves its thickening properties. Starch is modified not only for food but also industrial purposes. The concept of incorporating starch into plastic products also requires modification of starch because of its negative effects on water absorption and solubility of starch-plastic composite. ^ Cross-linking of starch in a batch system takes a long time and requires a drying process. Cross-linking of starch by reactive extrusion can reduce reaction time and eliminate the need for a drying process. The objectives of this study were to cross-link starch with phosphorus in an extruder, thereby reducing water absorption and solubility of starch. ^ In the first part, starch was extruded with water, 0.2 M sodium hydroxide and 2.5% sodium trimetaphosphate. The effects of moisture content of the feed and screw speed of the extruder on mean residence time, phosphorylation of starch, water absorption index, and water solubility index of starch were examined. Cross-linking of starch, with incorporated phosphorus, was confirmed by paste viscosity measurement. Minimum reaction time, adjusted by moisture content of feed and screw speed, for cross-linking of starch was determined. Cross-linking of starch with 0.2M sodium hydroxide and 2.5% sodium trimetaphosphate reduced the water solubility index but did not reduce the water absorption index significantly. ^ In the second part, starch was extruded with higher concentrations of sodium hydroxide and sodium trimetaphosphate. The effects of sodium hydroxide and sodium trimetaphosphate concentrations, at constant moisture content and screw speed, on phosphorylation of starch, water absorption index, water solubility index, radial expansions and bulk densities of extrudates were examined. The amount of phosphorus incorporated into starch was enhanced and water absorption index was reduced 40% at higher sodium hydroxide and sodium trimetaphosphate concentrations. ^ In the third part, twin-screw and single screw extruders, with and without a mixing elements were used for cross-linking of starch with phosphorus. The effect of extruder type and mixing element on phosphorylation, water absorption index, and water solubility index were studied. Replacement of the single screw extruder with a twin-screw extruder and use of a mixing element did not enhance the incorporation of phosphorus. ^
Agriculture, Food Science and Technology
Seker, Mahmut, "Phosphorylation of starch by reactive extrusion" (2001). ETD collection for University of Nebraska - Lincoln. AAI3022666.