food tests Flashcards
1
Q
How to test for proteins?
A
-Take a small volume of sample to be tested (2cm^3)
-Add an equal volume of biuret solution.
2
Q
Positive result for protein.
A
Blue -> purple (lilac)
3
Q
How to test for lipids?
A
- Take small volume of sample to be tested (2cm^3)
- Add an equal volume of ethanol (alcohol£ and shake.
- Ethanol will dissolve any lipids that are present.
- Pour this into an equal volume of water in another test tube.
4
Q
Positive result for emulsion test.
A
- If lipid is present, a cloudy white emulsion will be seen where lipid layer meets water layer.
5
Q
How to test for reducing sugar?
A
- Take small volume of substance to be tested (2cm^3)
- Add an equal volume of benedict’s solution.
- Heat in water bath at 85 degrees for 5 minutes.
6
Q
Positive result for reducing sugar test.
A
Blue -> brick red precipitate.
7
Q
How to test for non-reducing sugar test?
A
-When being negative w Benedict’s test, take a fresh sample (2cm^3) of substance.
- Add 5 drops of dilute HCl and place in water bath at 85 degrees celsius for 2 mins.
- Add pinch of sodium hydrogen carbonate to solution
- Use pH indicator, to check if pH is neutral.
- Redo benedict’s test.
8
Q
How to test for starch?
A
- Place 2 drops of substance to be tested into the well of a “spotting tray”.
- Add 2 drops of iodine solution.
9
Q
Positive result for starch.
A
yellow/brown -> blue/black
