Food Tests | Biology for GCSE/IGCSE - Year 11 PDF Download

Food Tests in Biology 

Test for glucose (a reducing sugar)

• Introduce Benedict's solution into the sample solution within a test tube.
• Heat the mixture within a water bath at a temperature range of 60 to 70°C for approximately 5 minutes.
• Remove the test tube from the water bath and observe any color changes.
• A positive result will be indicated by a transition in color from blue to either orange or brick red.

Test for starch using iodine

• Iodine can be employed to determine whether starch is present or absent in a food sample.

• To test for the presence of starch in a food sample, add drops of iodine solution to the sample. 
• A positive result will be indicated by a color change from orange-brown to blue-black.

Test for protein

• Add drops of Biuret solution to the food sample
• A positive test will show a colour change from blue to violet / purple

Test for lipids

• Food sample is mixed with 2cm³ of ethanol and shaken
• The ethanol is added to an equal volume of cold water
• A positive test will show a cloudy emulsion forming

Test for vitamin C

• Add 1cm³ of DCPIP solution to a test tube
• Add a small amount of food sample (as a solution)
• A positive test will show the blue colour of the dye disappearing