To Test for Starch, Protein, and Fats in Food (Class 10 Biology Practical)
To identify the presence of starch, protein, and fats in various food samples using specific chemical tests.
TL;DR: To identify the presence of starch, protein, and fats in various food samples using specific chemical tests.
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
Aim: To identify the presence of starch, protein, and fats in various food samples using specific chemical tests.
Materials Required
- Food samples (rice, egg, oil, milk, bread)
- Test tubes
- Iodine solution
- Biuret reagent (copper sulphate and sodium hydroxide)
- Sudan III/IV dye
- Distilled water
- Dropper
Theory
Different food components produce characteristic reactions with specific reagents: Iodine solution turns blue-black with starch (due to complex formation), biuret reagent gives a purple/pink color with proteins (due to copper chelation with peptide bonds), and Sudan dyes stain fats orange-yellow due to their lipophilic nature.
Procedure
- Label test tubes for each food sample
- Add a portion of each food sample to separate test tubes
- To test for starch: Add 2-3 drops of iodine solution and observe color change
- To test for protein: Add 2 mL of biuret reagent and observe color change
- To test for fats: Add 2-3 drops of Sudan III/IV dye and observe color change
- Record the color changes and results for each food sample
- Prepare a table showing which nutrients are present in which foods
- Note that some foods may contain multiple nutrients
Observation
Rice and bread samples turn blue-black with iodine, confirming presence of starch. Egg white and milk turn purple/pink with biuret reagent, indicating protein. Oil samples turn orange-yellow with Sudan dye, confirming presence of fats. Milk contains both protein and fats.
Result
The tests confirm the presence of starch in carbohydrate-rich foods, proteins in egg and milk, and fats in oils. Different food samples contain different combinations of these nutrients.
Precautions
- Use fresh reagents for accurate results
- Observe color changes against a white background
- Add reagents dropwise for clear observation
- Avoid direct contact of reagents with skin
- Dispose of chemical waste safely
Viva Questions
What color does starch turn with iodine?
Starch turns blue-black with iodine solution due to the formation of a complex.
What is the biuret test for?
The biuret test is used to detect proteins. It involves adding copper sulphate and sodium hydroxide solutions.
Why do fats stain with Sudan dye?
Fats are lipophilic (fat-loving) substances, so they readily dissolve in Sudan dyes which are also lipophilic.
Which food contains all three nutrients?
Milk contains proteins, fats, and carbohydrates (lactose), making it a complete food.
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