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GCSE Biology Booster Tutor: Food Tests

The testing of foods for presence of biological molecules in a range of foods.

· GCSE Science Notes


Macromolecules are large insoluble food molecules that need to be digested in order to be absorbed into the body’s system. The macromolecules are fats, carbohydrates, and proteins. The body requires these nutrients for various reasons. Fats are needed for energy and warmth. Proteins are needed for growth and repair and carbohydrates for energy.

The micro molecules are vitamins and minerals. These are needed for general health.


Food tests will identify the presence of carbohydrates, protein, and fats in food substances.

Starch (a carbohydrate) is detected using iodine solution. Iodine solution is red/brown in colour. Using a pipette a drop of iodine solution is added to the food substance to be tested. 

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The presence of starch will turn the iodine a blue/black colour.

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Reducing sugars, such as glucose, are detected using Benedict’s solution

Benedict’s solution is blue. The food substance is put into a boiling tube and Benedict’s solution added to it’. The boiling tube is placed into a beaker of hot water.

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If reducing sugars are present the Benedict’s solution gradually turns from blue to yellow, green, a cloudy orange or brick red.

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The yellow/green colouring suggests low levels of reducing sugars whilst the brick red colour shows high levels of reducing sugars.


Protein is detected using Biuret Reagent.

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The food substance to be tested is placed into a test tube. The biuret reagent is added. Presence of protein in the food will change the colour of the biuret reagent from blue to purple.


Lipids are detected using the emulsion test. The food substance to be tested into a test tube. 2cm3 of ethanol and 2cm3 of distilled water are added. Presence of lipids in the food will result in a milky-white emulsion forming.


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