From a practical perspective, the two most functional components are the starch and gluten, which together make up more than 85% of the total. Together the interaction of these two defining ingredients are what provides the unique properties of wheat flour and to a lesser extent related flours like rye, triticale, spelt etc.
STARCH - Wheat flour typically contains 70-75% starch and approximately 8 - 14% protein. Starch belongs to a group of chemical compounds called carbohydrates. Starch functions as a storage carbohydrate of plants such as cereals (wheat, maize, oats, rice and barley), tubers (potatoes, cassava) and pulses (peas and beans).
Starch is a regarded as a complex carbohydrate because it is made up of many sugar (glucose) molecules linked together to form chains, the two main ones being amylose and amylopectin. Amylose is a straight or linear chain of glucose molecules linked together, while amylopectin is a branched chain of sugars.
When viewed under a microscope, starch appears as a sphere between around 3 – 20 microns in size.
During milling, the large pressure exerted on the grain to crush the endosperm into flour results in some of these starch spheres being ruptured. This produces what is referred to as damaged starch. Damaged starch is capable of absorbing much more water than undamaged starch, but more importantly for breadmaking, once it is damaged, it is open to attack by enzymes which are able to break the starch down to sugar.
The diagrams to the right show the structure of amylose and amylopectin on a molecular level.
In order to be useful in the breadmaking process, some of the starch needs to be broken down into more simple sugars in order to feed the yeast used in most fermented products to provide the gas needed to aerate the dough. Starch is converted to sugar primarily through the action of enzymes, which may be either naturally present in the flour, produced by organisms present in the fermenting dough or added via an improver or enzyme active malt flour.
ENZYMES - Enzymes are present in all living things and are regarded as biological catalysts, i.e. they allow reactions to occur, but are not consumed in the process. Another unique feature of enzymes is that they are highly specific in their action – each enzyme is only capable of performing a single function. Enzymes are present in our saliva for example and are responsible for converting starch to sugar in the mouth, but our bodies contain dozens of other enzymes.
Enzymes are named with the first part of their name describing the type of activity they perform and the ending of the name always contains the three letters ….ase. Enzymes that act on starch are called amylases, with the prefix amyl... the term describing starch and ….ase indicating an enzyme. There are a number of different types of amylases, the principal ones being referred to as alpha and beta amylase.
Alpha-amylase can attack starch at most points along its chains, and in so doing produces smaller chains of various lengths. The smallest chain one unit long is glucose, while two units is maltose with larger units being referred to as dextrins. Beta amylase is capable of breaking dextrins down into maltose, which then needs to be converted to glucose by maltase, an enzyme produced by yeast. This is the yeast's means of ensuring an ongoing supply of glucose.