Amylopectin 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. 

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... 

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... 

The viscosity of a starch paste is mainly a function of the size of swollen granules. Waxy maize starch has smaller granules, so its swelling power is less than that of amylopectin potato starch. The peak viscosity of amylopectin potato starch, in comparison to potato starch and waxy maize starch, is shown in Figure 11.7. The gelatinization properties of amylopectin starch resemble those of potato starch. With reduced amylose content, the peak viscosity occurs as a lower temperature as swollen granules are weak and can be ruptured more easily with shear. 

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