Food Tests (Practical)

This lesson covers:

  1. How to prepare food samples for testing 
  2. The Benedict's test for sugars
  3. The Iodine test for starch
  4. The Biuret test for proteins 
  5. The Sudan III & emulsion tests for lipids 
Diagram showing the molecular structure of glucose.

Which test is used to detect the presence of reducing sugars (i.e. small sugars like glucose)?

Benedict's test

Biuret test

Bronchial test

Bartholomew's test

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Does the Benedict's test require heating the sample in a water bath? 

Yes

No

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Photos of Benedict's test

Test tubes showing Benedict's solution for reducing sugars with colours indicating no sugar, low concentration, medium concentration, and high concentration.

Benedict's solution itself in blue, but if reducing sugars are present then it will change colour depending on the concentration of reducing sugar.


Green indicates a low concentration of reducing sugar, orange indicates a medium concentration and brick-red indicates a high concentration.

What does iodine test for?

Proteins 

Lipids

Glycogen

Starch

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Iodine solution is used to test for the presence of starch. If starch is present, which colour change takes place?

Blue to lilac / purple

Orange to Pink

Blue to brick red

Orange to blue-black

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Illustration of a protein structure with various coloured shapes representing amino acids.

To test for proteins we can use solution.

biuret

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Biuret reagent can be used to test for the presence of proteins. If protein is present, what colour change takes place?

Orange to blue-black

Blue to lilac / purple

Blue to brick red

Orange to Pink

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Which reagent is used to test for the presence of lipids?

Iodine reagent

Benedict's reagent

Biuret reagent

Sudan III stain

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Sudan III test for lipids 


1 / 3 / 10 / red / pink / black


  1. Place 5cm3 of your food sample in a test tube.
  2. Add drops of Sudan III stain solution.  
  3. Gently shake.
  4. If a layer separates out on top, then lipid was present.
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red

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