Starch is the common name for the chemical compound amylose that consists of long chains of glucose molecules. Glucose is a sugar. When the body digests starch it converts it into glucose. In manufacturing food products such as corn syrup, manufacturers break down starch using enzymes derived from living organisms -- mirroring the process your body engages in when you consume starch.
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Amylose is a very large chemical made up of long chains of hundreds of glucose molecules, chemically bonded together. While glucose molecules are sugars and taste sweet, starch does not. This is because the starch molecules are too large to bind to sweetness receptors in the human mouth. Your body can burn glucose for energy, but you have no mechanism for absorbing amylose. As such, the first step in generating energy from starch is to digest it into glucose.
Starch digestion begins in the mouth. As you chew, you release saliva that contains an enzyme called salivary amylase, explains Lauralee Sherwood, M.D., in her book "Human Physiology." The salivary amylase breaks bonds between glucose units in starch molecules, starting the process of starch breakdown. This process continues in the small intestine. Your pancreas secretes additional amylase into the intestine that reacts with remaining starch molecules, breaking them down completely into nothing but glucose.
The chemical process of breaking starch into sugar is a relatively simple one at heart; the amylase enzyme assists in the reaction by inserting a water molecule into the space between two bonded glucose units. Water consists of two atoms of hydrogen and one atom of oxygen. The amylase enzyme breaks the bond between the glucose units, adding an oxygen and hydrogen to one end of the broken bond, and a hydrogen to the other end of the broken bond; this separates the glucose units, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry."
While living organisms can break down starch into glucose using amylase, it's also possible to simulate this process in a laboratory using enzymes extracted from bacteria and other organisms. For instance, when manufacturers make corn syrup from corn, they extract the amylose from the corn, and react the amylose, or corn starch, with amylase. This produces pure glucose, or corn syrup. Chemically, this process is identical to what occurs in the human digestive tract.