RPA 4:Test For carbohydrates, lipids and protein

Question 1

How do you prepare samples to test food groups?

Answer 1

• Crush food (pestle & mortar)
• Food in beaker + distilled water
• Mix with glass rod
• Filter solution (filter paper)

Question 2

How do you test for sugar?

Answer 2

Benedict’s test/solution

1. Add 2cm3 of the sample to be tested to a test tube. If the sample is not already in liquid form, first grind it up in water.
2. Add 2cm3 of Benedict’s reagent.
3. Heat the mixture in gently boiling water bath (750C) for 5 minutes.

Starting colour(negative result)-blue
Final colour(positive result)- very low: green, low: yellow, medium: brown, high: brick-red

Question 3

How do you test for lipids?

Answer 3

Emulsion Test
1. Add afew dropsof the liquid food sample to a dry test tube.
2. Add 2 cm3ethanoland shake it thoroughly.
3. Add 2 cm3 ofdistilled water.
Starting colour(- result)-colourless
Final colour(+ result)-milky white/cloudy

Question 4

How do you test for proteins?

Answer 4

Biuret test

1. Place a sample of the solution to be tested in a test tube
2. Add a few drops of biuret solution

Starting colour(- result)-blue
Final colour(+ result)-lilac/purple

Question 5

How do you test for starch?

Answer 5

Iodine test
Add a few drops of Iodine-Iodide Solution to test sample.

Starting colour(- result)-yellow/ brown
Final result(+ result)-blue-black