Food Tests

All chemicals are potentially hazardous: eye goggles must be worn

1. Take the food sample and grind with distilled water using a mortar and pestle. We want to make a paste.

2. Transfer the paste to a beaker and add more distilled water. Stir so the chemicals in the food dissolve in the water.

3. Filter the solution to remove suspended food particles.

Starch

• Add to test tube

• Add a few drops of iodine solution

• If starch is present, the orange iodine solution will turn blue/black

Sugars

• Add to test tube

• Add 10 drops of Benedict’s solution (which is a blue colour)

• Place test tube containing solution into a beaker and half-fill the beaker with hot water from a kettle

• Leave for around 5 minutes

• Green/yellow - small amount of sugar, red - lots of sugar present

• Only works for certain sugars (reducing sugars)

Protein

• Add 2cm3 to test tube

• Add 2cm3 of biuret solution (blue colour)

• If protein is present, will turn to a purple or lilac colour

Lipids

• Don’t filter solution

• 2cm3 added to test tube

• Add a few drops of water and a few drops of ethanol

• Gently shake

• White cloudy emulsions form if lipids are present