amylose

Definition: Amylose is a linear polymer of glucose linked mainly by α(1→4) bonds. It can be made of several thousand glucose units. It is one of the two components of starch, the other being amylopectin. Amylose is soluble in water.

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) is usually in the range of 300 to 3000, but can be many thousands.

Amylose starch is less readily digested than amylopectin; however, it takes up less space so is preferred for storage in plants. It makes-up about 30% of the stored starch in plants, though the specific percentage varies by species. The digestive enzyme amylase breaks down the starch molecule into maltotriose and maltose.

Iodine molecules fit neatly inside the helical structure of amylose, binding with the starch polymer that absorbs certain known 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 color will be observed. The intensity of the color can be tested with a colorimeter, using a red filter to discern 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.