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They are called this because they contain only carbon, hydrogen and oxygen. Pure dry starch is a white granular powder. Wheat flour contains 70-73% starch and most commonly anywhere between 8 -14.5% protein.
If you look at flour under a microscope you can see lots of brick like structures called cells. In each cell you will see a granule of starch surrounded by glassy looking protein. Different types of starch have different structures. Potato starch is oval in shape, wheat starch is oval or round but smaller than potato starch, and maize starch has a “rocky” look.
Starch is called a complex carbohydrate because it is made up of many sugar molecules linked together. It has two main parts: amylose and amylopectin.
Amylose is a straight or linear chain of sugar molecules linked together.
Amylopectin is a branched chain of sugars.
Starch is a storage carbohydrate of plants such as cereals (wheat, maize, oats, rice and barley), tubers (potatoes, cassava and taro) and pulses (peas and beans). In whole wheat grains it makes up 60-70% of the grain. It is found in the endosperm which is the part of the grain that white flour is milled from.
Starch and the products derived from it are used in the food, brewing, pharmaceutical, paper, textile and adhesive industries.
In the food industry starch is used as a thickener, filler, binder and stabiliser in products such as soups, custard powders, pie fillings, sausages and processed meats, ice cream, sauces and gravies, baby foods, bakery products and baking powder.
The pharmaceutical industry use it in the manufacture of pills. It is used as a filler because it is bland and odourless. The textile industry uses starch for coating the fibre before weaving, and the dye pastes used for printing have starch in them. In the paper industry a starch solution is applied to surfaces of paper to increase the strength of the paper and give it a better finish. Starch also makes a very good adhesive or glue and is used to make cardboard cartons, boxes and containers. The gum used on the back of stamps and on envelope flaps is also made from starch.