Food Test | Biology for JAMB PDF Download

Iodine Test for Starch Detection

The iodine test is used to detect the presence of starch in food samples. Starch is a complex carbohydrate found in many plant-based foods such as rice, potatoes, and bread. To perform the iodine test, follow these steps:

• Take a small amount of the food sample in a test tube or on a white tile.
• Add a few drops of iodine solution (commonly known as Lugol's solution) to the food sample.
• Observe the color change. If the sample turns dark blue or black, it indicates the presence of starch.

Biuret Test for Protein Detection

The biuret test is used to detect the presence of proteins in food samples. Proteins are essential macromolecules found in various animal and plant-based foods. To conduct the biuret test, follow these steps:

1. Take a small amount of the food sample in a test tube.
2. Add a few drops of 1% copper sulfate solution to the sample.
3. Next, add a few drops of 10% sodium hydroxide solution (NaOH) to the mixture.
4. Gently mix the contents and observe the color change. If the sample turns violet or purple, it indicates the presence of proteins.

Benedicts Test for Sugar Detection

The Benedicts test is used to detect the presence of reducing sugars in food samples. Reducing sugars include glucose, fructose, and maltose, which are commonly found in fruits, honey, and some vegetables. To perform the Benedicts test, follow these steps:

1. Take a small amount of the food sample in a test tube.
2. Add an equal volume of Benedicts solution to the sample.
3. Heat the mixture in a boiling water bath for a few minutes.
4. Observe the color change. If the sample changes from blue to green, yellow, orange, or brick-red, it indicates the presence of reducing sugars.

Ethanol Test for Lipid Detection

The ethanol test is used to detect the presence of lipids (fats and oils) in food samples. Lipids are essential dietary components found in foods like butter, vegetable oils, and fatty meat. To conduct the ethanol test, follow these steps:

1. Take a small amount of the food sample in a test tube.
2. Add an equal volume of ethanol (ethyl alcohol) to the sample.
3. Gently shake or mix the contents.
4. Observe the solution for any cloudiness or the formation of a white precipitate. It indicates the presence of lipids.

Note: The mentioned tests are commonly used in food analysis to detect specific macromolecules. When performing these tests, it is important to follow appropriate safety precautions and use the correct concentrations of reagents.