Amylose
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Amylose (CAS# 9005-82-7) is a linear polymer of glucose linked with mainly α(1→4) bonds. It can be made of several thousands of glucose units. It is one of the two components of starch, the other being amylopectin.
The α(1→4) bonds promote the formation of a helix structure. The structural formula of amylose is pictured at right. The number of repeated glucose subunits (n) can be many thousands (usually in the range of 300 and 3000).
Amylose starch is less readily digested than amylopectin. However it takes up less space so is preferred for storage in plants; it is how about 20% of the starch in plants is stored. The digestive enzyme amylase works on the ends of the starch molecule, breaking it down into sugars.
Iodine molecules fit neatly inside the helical structure of amylose, binding with the starch polymer, causing it to absorb certain wavelengths of light. Hence, a common test for starch is to mix it with a small amount of yellow iodine solution. In the presence of amylose a blue-black colour will be observed. The intensity of the colour can be tested with a colorimeter using a red filter, to indicate the concentration of starch present in the solution.
High-amylose varieties of rice have a much lower glycemic load which could be beneficial for diabetics.
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