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ABSTRACT
The structure and physicochemical properties of waxy, common, and high-amylose corn starch phosphates prepared by oven heating were studied. Starch phosphates prepared by either slurry or dry-mixing treatment before oven heating were also compared. The slurry treatment more efficiently incorporated phosphorus into starch relative to the dry-mixing treatment under the reaction conditions studied. In general, the phosphorylated starch prepared by the slurry treatment exhibited a lower gelatinization temperature, a higher peak viscosity, a lesser degree of retrogradation, and improved freeze-thaw stability compared with those prepared by the dry-mixing treatment. Phosphorylation occurred probably in both amylose and amylopectin, and the amount and location of incorporated phosphate groups varied with starch types likely due to their different amylose and amylopectin contents. Waxy starch was more prone to phosphorylation, followed by common and high-amylose starches, respectively.
Cereal Chem. 82(3):264-270
The utilization of native starch in foods is limited by its physicochemical properties. Starch granules are insoluble in cold water and heat is required to achieve dispersion. Cooked native starch has a high viscosity that is not desirable in certain applications; it normally imparts a gummy, cohesive texture to food and tends to lose its viscosity and thickening power on further heating. Furthermore, retrogradation is a common feature of cooled starch paste, characterized by losing its water binding capacity, resulting in syneresis and water separation.
Chemically modified starches show markedly altered physicochemical properties as compared with the parent starches (Rutenberg and Solarek 1984). Phosphorylation is one of the starch modification methods designed to overcome the shortcomings mentioned above. The introduction of negatively charged phosphate groups reduces interchain associations and facilitates starch hydration. Starch phosphates can be grouped into two classes: monostarch phosphate and distarch phosphates. Starch phosphate monoester is formed when one starch hydroxyl group is esterified to phosphate. Starch phosphate diester is formed when two starch hydroxy groups are esterified to the same phosphate group. During phosphorylation, pH plays a dominant role in determining the ratio of starch monoester to diester. Phosphate monoesters are produced in a pH range of 5.0-6.5 with mixtures of orthophosphates and a pH range of 5.0-9.0 with sodium tripolyphosphate (STPP) (Kerr 1947). Lim and Seib (1993) reported that phosphorylated starch prepared at pH 9.5 showed better heat and shear stability...