Question

Thickening agents are flavorless starches or proteins commonly used in cooking; such as thickening gravy for Thanksgiving dinner. Why would you suspect corn starch is a common thickening agent?

Answer 1

Chemically, starches are little more than chains of sugar molecules strung together. This is a convenient way for a plant to store energy. It is no accident that these are stored in seeds and roots, because these are where energy is most needed. Starches in seeds supply the energy for germination; they continue supplying energy until the first leaves emerge and photosynthesis begins. Likewise, energy is needed in the roots for the roots to grow and transport fluids. Plants generally have a mixture of two different types of starches. Amylose is a straight chain of sugar molecules. Amylose pectin is a branched chain of sugar molecules. When you look at a starch, you are really seeing millions of these molecules packed together in discrete granules. The proportion of these different molecules in a plant differs in different species.

If you put a tablespoon of starch into a cup of cold water, nothing will happen because the granules do not dissolve. However, if the water is hot, the heat disrupts the granules and causes hydrogen bonds to form between the water and the starch.