2.2.12

Required Practical - Testing for Food Chemicals

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Testing for Carbohydrates, Lipids and Proteins

The objective of this experiment is to use qualitative reagents to identify the presence of food chemicals such as sugars, starch and proteins. The tests only tell if a substance is present, not how much.

Test for sugars (Benedict’s test)

Test for sugars (Benedict’s test)

  • Add Benedict’s solution to the food sample.
  • Heat gently in a water bath for a few minutes.
  • Observe the colour change.
    • A red-brown precipitate forms if reducing sugars (like glucose) are present.
  • Hazards:
    • Benedict’s solution is an irritant.
    • Wear safety goggles, avoid contact with skin and eyes.
Test for starch (Iodine test)

Test for starch (Iodine test)

  • Add a few drops of iodine solution to the food sample.
    • For example, peel a potato and drop iodine onto it.
  • Observe the colour change.
    • If the food turns to a blue-black colour, there is starch present.
  • Hazards:
    • Iodine is an irritant.
    • Wear goggles, avoid contact with skin and eyes.
Test for proteins (Biuret test)

Test for proteins (Biuret test)

  • Add 1 cm3 of Biuret solution A to the food sample and mix.
  • Add 1 cm3 of Biuret solution B, shake or allow layers to form.
  • Observe the colour change.
    • A purple colour or a ring between layers means protein is present.
  • Hazards:
    • Biuret A is corrosive; Biuret B is an irritant.
    • Wear goggles and handle carefully.
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1

Cell Biology

1.1

What's in Cells?

1.2

Cell Division

1.3

Transport in Cells

2

Organisation

2.1

Principles of Organisation

2.2

Enzymes

2.3

Circulatory System

2.4

Non-Communicable Diseases

2.5

Plant Tissues, Organs & Systems

3

Infection & Response

4

Bioenergetics

5

Homeostasis & Response

5.1

Homeostasis

5.2

The Human Nervous System

5.3

Hormonal Coordination in Humans

5.4

Plant Hormones

6

Inheritance, Variation & Evolution

6.1

Reproduction

6.2

Variation & Evolution

6.3

Genetics & Evolution

6.4

Classification

7

Ecology

7.1

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7.2

Organisation of Ecosystems

7.3

Biodiversity

7.4

Trophic Levels

7.5

Food Production

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