Aim: In this practical, you will carry out a series of tests to identify the presence of different types of nutrients in various food samples. These tests include identifying sugars, starch, proteins, and lipids.

Method:

1. Test for Reducing Sugars (Benedict's Test):

• Step 1: Add a small amount of the food sample to a test tube.
• Step 2: Add 2-3 cm³ of Benedict's solution to the test tube.
• Step 3: Place the test tube in a hot water bath (around 75°C) for 5 minutes.
• Positive Result: If reducing sugars are present, the solution will change from blue to brick-red or orange.

2. Test for Starch (Iodine Test):

• Step 1: Place a small sample of food on a spotting tile or in a test tube.
• Step 2: Add a few drops of iodine solution to the sample.
• Positive Result: If starch is present, the solution will change from brown to blue-black.

3. Test for Proteins (Biuret Test):

• Step 1: Add a small amount of the food sample to a test tube.
• Step 2: Add 2-3 cm³ of Biuret solution (a mixture of sodium hydroxide and copper(II) sulfate) to the test tube.
• Step 3: Gently shake the test tube to mix.
• Positive Result: If protein is present, the solution will change from blue to purple.

4. Test for Lipids (Emulsion Test):

• Step 1: Add a small amount of the food sample to a test tube.

• Step 2: Add 2 cm³ of ethanol and shake the test tube thoroughly to dissolve any lipids.

• Step 3: Add 2 cm³ of distilled water to the test tube.

• Positive Result: If lipids are present, a cloudy white emulsion will form. Alternative Lipid Test (Sudan III Test):

• Step 1: Add a small amount of the food sample to a test tube.

• Step 2: Add 2-3 drops of Sudan III stain solution and gently shake.

• Positive Result: If lipids are present, a red-stained oil layer will form on the surface.

Conclusion: These tests allow you to identify the presence of key nutrients in food samples. By knowing which nutrients are present, you can better understand the nutritional content of different foods and how they contribute to a balanced diet.