Biology · 4.2 Biological molecules · Paper 5/6 practical
Food Tests. Read the colour.
Five chemical tests identify the nutrients in a food: iodine for starch, Benedict's for reducing sugars, biuret for protein, the ethanol emulsion test for fats, and DCPIP for vitamin C. Apply a reagent and read the colour change.
0610 — Food tests
iodine · Benedict's · biuret · DCPIP
Paper 5/6 — Practical
no test applied
Food sample
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Result
Test
none
Tests for
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Observation
apply a test…
Results log
Run tests to build the food's nutrient profile.
📋 The five tests & positive results
- Starch — add iodine solution: orange-brown → blue-black.
- Reducing sugar — add Benedict's solution and heat in a water bath: blue → green → yellow → orange → brick-red (colour shows how much sugar).
- Protein — add biuret reagent: blue → purple/violet.
- Fats & oils — shake with ethanol then add water: a cloudy white emulsion forms.
- Vitamin C — add the sample to blue DCPIP: the dye is decolourised (the more vitamin C, the fewer drops needed).
⚠ Safety & precautions
- Heat Benedict's in a water bath (electric or beaker of hot water), not a direct flame — ethanol and some samples are flammable.
- Wear eye protection; biuret/sodium hydroxide is corrosive.
- Use a control (e.g. distilled water) to show the colour of a negative result.
- Cut solid foods up and shake/grind with water to release the nutrients first.
🎯 Syllabus reference (0610)
- Describe the use of: iodine solution to test for starch; Benedict's solution to test for reducing sugars; biuret test for proteins; ethanol emulsion test for fats/oils; DCPIP for vitamin C.