Amylose swelling

Starch is the main thickener in gravies, sauces, and puddings. It absorbs water, and becomes a gel when cooked. As the starch swells up with water, the amylose leaches out, and the amylopectin forms the gel. Some starches have higher amylopectin content and make better gels than those containing large amounts of amylose. 

In these plant organs, starch is present in the form of microscopically small granules in special organelles known as amyloplasts. Starch granules are virtually insoluble in cold water, but swell dramatically when the water is heated. Some 15-25% of the starch goes into solution in colloidal form when the mixture is subjected to prolonged boiling. This proportion is called amylose ( soluble starch ). 

When starch is heated in excess water, the crystalline structure is disrupted (due to breakage of hydrogen bonds) and water molecules become linked by hydrogen bonding to the exposed hydroxyl groups of amylose and amylopectin. This causes an increase in granule swelling... 

Starch source Amylose content (%) Swelling power (g/g) (°C) Solubility (%) (°C) Organic ph osphorus contents (% dsb) Light transmittance (%, at 650 nm)... 

The "selective absorption method employed by Ashford et al(Refs 5 6) in the study of starch avoids the use of harsh swelling agents but employs adsorbing agents (such as cotton activated charcoal or Fuller s earth) to remove amylose from amylopectin when in aq soln. The cotton-amylose adsorbate is formed instantly when a cold corn starch paste(2%) is brought into contact with cotton and can be washed free of amylopectin with w. The cotton-adsorbate is then readily decomp by boiling w to give a clear soln of amylose and the solid is obtained by con eg the soln to... 

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