Amylopectin covalent phosphate

As we have previously stated, most starch granules are composed of amylose and amylopectin in a ratio of 1 4 or 1 3. Tuber starches in addition contain covalently linked phosphate potato starch has 0.06%, and shoti starch has 0.18% covalent phosphate [30a]. The cereal starches are devoid of phosphate but contain 1-5% lipid [30b], which is believed to be complexed with the amylose component in a helical structure. 

Amylose, although water soluble, gives an unstable solution which irreversibly precipitates. It is mainly responsible for the deep blue coloration given by starch and iodine. Solutions of amylopectin are relatively stable. The iodine-binding capacity, on the other hand, is very low. A small amount of covalently bound phosphate normally appears with starch but its exact location within the molecule is not known. 

Crystalline human salivary a-amylase produced 6 -phosphomaltotetraose from potato amylopectin, demonstrating that the covalently linked phosphate in potato starch was attached to the C-6 hydroxyl group by a phosphoester linkage in amylopectin [23]. 

Amylopectin contains a small quantity of covalently linked phosphate as a 6-ester, which cannot be removed without extensive degradation of the polysaccharide. ) -Amylol is does not remove this phosphate, which remains in the limit dextrin. It has been shown that although a-D-(i ->-4) and a-D-(i ->6) linkages predominate in amylopectin, a very small number of a-D-(i - 3) links also occur. 

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