B2 Food Tests Flashcards
How do u test for the presence of starch
Make a food sample and transfer 5cm³ of ur sample to a test tube. Then add a few drops of IODINE solution and gently shake the tube to mix the contexts. If the sample contains starch the colour of the solution should change from BROWNY-ORANGE to BLACK/BLUE-BLACK
How do we test is protein is present in food
We can use the biuret test.
We transfer 2cm³ of our food sample to a test tube and then add 2cm³ of BIURET solution to the sample and mix the contents of the tube by gently shaking it. If the food sample contains protein the solution will change from BLUE To PURPLE/LILAC.
If no protein is present the solution will stay blue.
How do we test for Reducing Sugars e.g Glucose in a food test
Prepare your food sample and place in a test tube. Prepare a water bath and heat to 70-75°. Then add some BENEDICTS solution to the test tube (around 10 drops) using a pipette. Then place the test tube in the water bath and leave it there for 5 minutes - make sure the test tube is pointing away from us -. The solution in the test tube will change from the normal BLUE To GREEN,YELLOW BRICK RED depending on how much sugar is in the food.
How do we test for fats and lipids in a food sample
We can use the elmusion test.
Place our food sample inside a test tube, add few drops/around 2cm³ of ETHANOL and a few drops of distilled WATER then shake it. If lipids are present it will turn from CLEAR to CLOUDY.
Before every food test we need to prepare the food sample, How do we do this.
- Take the food sample and grind this with distilled water using a Mortar and Pestle, in order to make a paste, to soon be a solution.
- Transfer the paste to a beaker and add more distilled water. Stir so the chemicals in the food dissolve In the water.
- Then filter the solution using a filter funnel lined with filter paper to remove the suspended food particles.
What is the only test when preparing the food sample we don’t filter the solution and why?
The emulsion test/ When testing for lipids, as the lipid molecules can stick to filter paper
What are the 4 tests and what do they test for + colour change.
Benidicts test - tests for reducing Sugars (Blue to Yellow,Green or brick Red).
Iodine test - tests for Starch (orangy-brown to blue black).
Biuret test - tests for proteins (Blue to Purple/Lilac).
Emulsion test - for lipids (Clear to Cloudy)
What is a safety precaution of the Elmusion test.
Make sure no naked flames are present or near as ethanol is very flammable.
When doing the benedict test why should the test beaker containing the solution be pointing away from whoever is carrying out experiment
As the test tube is in a solution over a bunsen burner there is a good chance if the tube is facing the person there is a risk of the solution boiling over or splashing out of the test tube onto whoever is doing the experiment.
Placing the test tube away at an angle minimises the risk of accidently knocking over the test tube or spilling the solution onto oneself.
