Food Tests

Question 1

Benedict Test?

Answer 1

Used to test for sugars.

1. Add Benedict solution to food
2. Heat in water bath.
3. Benedict solution changes colour when heated :red,yellow,orange, green and brown depending how much glucose there is.
4. Sugars classed as reducing sugars will react with Benedict’s solution on heating for a few minutes. Glucose is an example of a reducing sugar.

Reducing sugars give a red-brown precipitate with Benedict’s solution. The precipitate takes a while to settle in the tube – you’re more likely to see simply a red or brown colour. If there’s not much glucose present, the final colour may be green or yellow, or orange if there’s a little more.

Question 2

Iodine test?

Answer 2

Add iodine solution to the food being tested. Foods containing starch will turn a blue-black colour.

The iodine test can also be used with a microscope to stain starch grains in plant cells.

Hazards
Wear safety goggles.
Iodine solution is an irritant.
Avoid contact with skin and eyes.

Question 3

Biruet test?

Answer 3

The biuret test is used to detect proteins.

Biuret reagent is sometimes available as a single solution.

Method
Add 1 cm3 of biuret solution A to the food solution.
Mix the liquids.
Add 1 cm3 of biuret solution B and shake.
-A purple colour indicates protein is present.
-A purple ring between the layers indicate protein is present.

Question 4

Emulsion/Ethanol test?

Answer 4

Is a test for lipids.
1.Ethanol is add to a test tube with crushed food in
it
2.This solution is added to another test tube containing
water leaving a food residue behind.
3.A cloudy emulsion will form if lipids present.