food test

• Preparing a sample

  • Before you can carry out any of the food tests described below, you may need to prepare a food sample first (especially for solid foods to be tested)
• • To do this:
  • Break up the food using a pestle and mortar
  • Transfer to a test tube and add distilled water
  • Mix the food with the water by stirring with a glass rod
  • Filter the mixture using a funnel and filter paper, collecting the solution
  • Proceed with the food tests
• Test for sugars

  Benedict's test is used to detect sugars.
• Heat in a water bath - benidicts sugars
• After heating, it may go through stages - green, yellow, orange, red or brown - depending on how much glucose is present
• Carbohydrates


  One of the major nutrients required for a healthy diet
• Proteins

  One of the major nutrients required for a healthy diet
• Lipids

  One of the major nutrients required for a healthy diet
• Digestive system

  1. Breaks down large molecules of food

  2. Absorbed into the bloodstream
• Qualitative tests

  • Results that are not expressed as numbers or numerical data, eg they can be expressed as present or absent, or as colours
• Quantitative analysis

  Results that can be expressed using numerical values
• Benedict's test


  1. Used to detect sugars

  2. Heat in a water bath

  3. May go through stages - green, yellow, orange, red or brown - depending on how much glucose is present
• Reducing sugars


  Sugars that act as reducing agents. Glucose, fructose, lactose and maltose are reducing sugars. Sucrose is a non-reducing sugar.
• Precipitate


  A suspension of particles in a liquid formed when a dissolved substance reacts to form an insoluble substance, eg in a precipitation reaction.
• Iodine test


  1. Add iodine solution to the food being tested

  2. Foods containing starch will turn a blue-black colour
• Proteins


  Organic compound made up of amino acid molecules. One of the three main food groups, proteins are needed by the body for cell growth and repair.
• Biuret test


  1. Add 1 cm3 of biuret solution A to the food solution

  2. Mix the liquids

  3. Add 1 cm3 of biuret solution B and shake OR add 1 cm3 of biuret solution B carefully down the side of the test tube so as to form two layers
• Lipids


  Fat or oils, composed of fatty acids and glycerol.
• Sudan III test


  If lipid is present in the sample, it stains red
• Emulsion test

  An alternative test for lipids