Food tests

• 1. Take the food sample and grind this with distilled water using a morta and pestle. This will 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
• Testing for starch


  Place 2cm3 of food solution in a test tube and then add a few drops of iodine solution (which is an orange colour). If starch is present then the iodine solution will turn blue-black, however if there is no starch present then the iodine solution will stay orange
• Testing for sugars 


  Place 2cm3 of food solution in a test tube. Add 10 drops of Benedict's solution (which is a blue colour). Put the test tube inside of a beaker and half-fill the beaker with hot water. Leave this for around 5 minutes. If sugars are present in the Benedict's solution then the solution will change colour. The colour of the Benedict's solution gives us an approximate idea of the amount of sugar present. If it is green then there is a small amount of sugar. If it is yellow then there is more sugar present and if it is brick-red then there is a lot of sugars
• Testing for proteins


  Take 2cm3 of food solution and add 2cm3 of biuret solution (which is a blue colour). If protein is present then the biuret solution will change from blue to a purple colour
• Testing for lipids/fats


  Do not filter the solution because lipid molecules can stick to filter paper. Put 2cm3 of food solution in a test tube. Add a few drops of distilled water and a few drops of ethanol. Gently shake the solution. If lipids are present, then a white cloudy emulsion forms