Saturday, 27 September 2014


 Starch comes from plants, it is a carbohydrate and therefore made up of carbon, hydrogen and oxygen. It consists of a large number of glucose molecules joined together. This polysaccharide is produced by most green plants. It is important to have starch in the diet because it gives energy. It is the most common carbohydrate in human diets and is contained in large amounts in foods like potatoes, wheat, rice etc.

  While being chewed, starch is already beginning to be changed into sugar, which can easily be absorbed by the body. The enzymes that break down starch into the constituent sugars are known as amylases. Human saliva is rich in amylase, consequently digestion of starch begins in the mouth. The pancreas also secretes this enzyme in pancreatic juice.

 This experiment has two parts. In the first part we identify what food contains starch and in the second part we determine starch content in bread before and after mixing it with saliva.
Iodine preparation

 For this experiment we need a variety of foods and iodine. Iodine changes colour when is put in contact with starch. We add a few drops of iodine on food and observe the colour change.

 As you can see in the picture, the foods that change colour are potato, rice, pasta and bread. These are rich in starch. Salt and apple don’t change colour. Some processed foods like sausages, chopped pork or some cheeses contain starch as a thickening agent.

 Now we put a piece of bread in our mouths for a few minutes and mix it well with saliva. After a while we put in on a plate next to a dry piece of bread. After adding iodine we observe that the bread mixed with saliva doesn’t change colour or changes only slightly. This is because the amylase in saliva has broken down the carbohydrate. Sometimes you can notice a sweet taste after having bread in your mouth for a while, because starch has been broken down into its sugar components.

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