Practicles Flashcards
What is the purpose of the Biuret test?
To test for the presence of proteins
The Biuret test is a chemical test used to detect the presence of peptide bonds, which are indicative of proteins.
How much food solution is used in the Biuret test?
3 cm³
A clean syringe is used to add the food solution to the test tube.
What is the volume of Biuret solution added in the test?
3 cm³
A clean plastic pipette is used for adding the Biuret solution.
What color indicates a negative result in the Biuret test?
Blue
This indicates that proteins are absent in the food solution.
What color indicates a positive result in the Biuret test?
Violet
This shows that proteins are present in the food solution.
What happens to the color of the solution in a positive Biuret test?
Pale blue turns to violet
The change in color is a visual indicator of protein presence.
What remains unchanged in a negative Biuret test?
Pale blue
This indicates that no proteins are present in the sample.
Fill in the blank: A _______ result for protein shows the pale blue colour turns to violet.
Positive
A positive result indicates the presence of proteins in the sample.
Fill in the blank: A _______ result for protein stays pale blue.
Negative
A negative result indicates that proteins are absent in the sample.
What is the method of a biuret test?
- Get 3cm of the food sample solution and add to to an empty test tube
- And 3cm of the biuret solution using a clean pipes into the test tube and swill side to side
- If it’s positive it will show violet liquid if it’s negative there will be no colour change and it will stay blue
What is the lipids plus ethanol test?
It test for lipids/oils
METHOD
1. Put 2cm of the food solution into a clean test tube using a syringe
2. Add 2cm of ethanol into the test tube using a puppet
3. Fill another clean test tube up will water until it’s half full
4. Shake the ethanol solution well with a lid on and add to the water
5. If you see four layer bubbles, oil, cloudy and water it is a positive solution of lipids
6. If the whole thing is cloudy then it’s negative
How do you Test for Starch
• Put a few drops of the food solution into the spotting tile
• Add two or three drops of iodine solution to the food
sample
• A positive result is when a blue black colour is seen - starch is
present
• A negative result is when there is no colour change and it stays brown
How do you Test for (Reduced) Sugar?
● Put about 5cm3 of food solution into a test tube
● Add 5cm3 of Benedict’s solution to the food sample which should show a blue colour.
● Put the test tube into a beaker of hot water for a few minutes
● A positive result is when the blue colour turns orange or red - glucose is present
● A negative result is when there is no colour change
