Kitchen Chemistry: What is Starch? Why You Should Care

Starch is a vital part of life. Commercially obtainable starches come from the plant world. Many foods contain such a prevalence of starch as to actually be called starches themselves.

Sources of Edible Starch

Foods we eat everyday contain the chemical substances we call starch. Potatoes have starch. Rice has starch. Wheat in bread has starch. Some foods contain such a large percentage of starch that we call them starches. Thus, our diet always contains starch.¹

On the other hand, dress shirts are often treated with starch. Dry Cleaners may ask, "Do you want your collars or your shirts starched?" Because of this, and because eating and laundering are such different processes, someone might ask, "Are these starches the same thing, or are they different? Is food starch the same as laundry starch?"

Chemically, What is Starch?

To begin with, let's define what the starch in foods actually is. Wikipedia tells us, "The word "starch" is derived from Middle English sterchen, meaning to stiffen. " Likely you know that starches are sometimes used in making gravies or sauces. Why is that? Because starch, in the presence of moisture and heat, first dissolves, then thickens the liquid they are absorbed in by a process termed gelatinization.

Starch is basically a polysaccharide. So what is a polysaccharide? The prefix poly- means many. Starch consists of many monosaccharide groups attached to each other. What then is a monosaccharide? Basically, it is one sugar molecule. Simple sugars such as glucose, galactose, and fructose are monosaccharides. Two saccharide units link together to form disaccharides. Sucrose, or table sugar, is one of these. Monosaccharide sugars may link together in various fashions to make up a polysaccharide. Some of these polysaccharides, again, are called starch.

Two Starch Components

Another word for saccharides, whether monosaccharides or polysaccharides, is carbohydrate. You will recognize these as part of our daily diet. Foods frequently contain two starch types. Amylose and amylopectin. Most plant starches contain about 1/4 amylose and 3/4 amylopectin.²

Properties of Starch

We have already discussed the thickening property of starches. In addition, since we recognize that sugars are a source of energy, it must be apparent that starches are sources of energy. Starches require more chemical processing by our bodies, so it becomes obvious that starches provide a lower threshold of energy that lasts for a longer period of time.

Why is Starch Used on Clothing?

So what about the starch used for clothing? It is the same as the starch in foods. Starch is used in shirts and other garments where neat and stiff is considered a plus. In addition, perspiration is absorbed by the starch, rather than the fibers of the garment, and thus clothes come out cleaner and fresher-smelling. So when you hear the word carbohydrate, think of the beneficial energy of sugar, but also think of the energy starches provide, as well as the fine additional properties of thickening to make gravies and sauces, and the cosmetically-pleasing appearance and ease of cleaning of the garments it has been used to treat.

¹ To see images of starch molecules, please examine the upper left-hand portion of this page.

² Brown WH & Poon T, (2005), Introduction to Organic Chemistry (3rd ed., John Wiley & Sons).