Question

How to know the presence of starch in any given sample of food?

Answer 1

Hint: The main carbohydrates found in our food are in the form of starch and sugars The major sources of starch are cereals like rice, wheat, maize and root vegetables like potatoes. To know the presence of starch in any given sample of food, the iodine test can be conducted. In this, an iodine solution is used.

Complete answer:
We can easily test if a food item contains starch using the Iodine test. Take a small quantity of the food items to be tested. Then add 2-3 drops of iodine solution to it. Observe the colour change of the food item. If starch is present in the food, the colour of the sample taken will change to Blue-black colour. If starch is absent in a food item, it will remain brown in colour. The iodine-starch test is a chemical reaction that is used to test for the presence of starch or for iodine. The combination of starch and iodine is intense “blue-black”. The interaction between starch and triiodide is the basis for iodometry. Starch is often used as an indicator in redox titrations. Starch forms a very dark blue-black complex with triiodide. However, the complex is not formed if only iodine or only iodide is present.

Additional Information: -Carbohydrates are the most abundant organic compounds in nature. They are polyhydroxy carbonyl compounds. Starch, glycogen, chitin, cellulose and dextrans are polysaccharides.
-Starch is a storage form of plant polysaccharide, especially abundant in tubers, corms etc.
-Starch is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds.

Note: -Starch is the most common carbohydrate in human diets and is contained in large amounts in staple foods like potatoes, maize, rice, wheat etc.
-In industry, starch is converted into sugars, for example by malting, and fermented to produce ethanol in the manufacture of beer, whisky and biofuel.
-It is processed to produce many of the sugars used in processed foods.