Food Tests Flashcards
1
Q
How do you test for starch?
A
- Place one spatula of the food sample or starch solution on a dish (or well in a spotting tile)
- Using a dropper, place a few drops of iodine onto the food
- Record any colour change
If starch is present, the iodine solution will go from orange or yellow to blue-black.
2
Q
How do you test for reducing sugars?
A
- Place two spatulas of the food sample or 1cm^3 if the sample is liquid, into a test tube. Add about 1cm^3 depth of water to the tube and stir to mix.
- Add an 1cm^3 of Benedict’s solution and mix
- Place the test tube in a water bath at about 95 degrees Celsius for a few minutes
- Record any colour change of the solution
If reducing sugar is present, the Benedict’s solution should gradually turn from blue to green to yellow to cloudy orange to brick red.
3
Q
Reducing sugars include:
A
- monosaccharides - such as glucose or fructose
- disaccharides - such as maltose
4
Q
How do you test for protein?
A
- Place two spatulas of food sample into a test tube or 1cm^3 if the sample is liquid. Add about 1cm^3 depth of water to the test tube and stir to mix
- Add an equal volume of potassium hydroxide to the test tube and stir
- Add two drops of copper sulphate and stir for two minutes
- Record any colour change of the solution
If protein is present, the solution turns mauve or purple from pale blue.
5
Q
How to test for lipids?
A
- Place 2 spatulas or 1cm^3 of food solution into a test tube
- Add 2cm^3 of ethanol. Cover the end of the tube and shake well/vigorously
- Add an equal volume of distilled water
- Record the colour change, or whether it is cloudy or clear
If a lipid is present, a milky-white emulsion will form from the colourless solution.
6
Q
Risks of the food tests
A
- Potassium hydroxide can be harmful to skin and eyes
- Hot water can scald
- Ethanol is highly flammable
- Benedict’s solution is harmful in the event of contact with the skin
