Food tests
Use chemical tests to identify starch, sugar, protein, and lipids in foods.
Check your understanding with these quick common questions. Use the drop down boxes to see the correct answers.
Glucose is a carbohydrate.
Starch is built from many glucose molecules
Proteins are made of many amino acids.
Lipids are made of fatty acids (a hydrocarbon chain) and glycerol (a type of sugar).
Do not confuse lipids and fats. Lipids is the correct word to use. Fats are a type of lipid. Cholesterol is another type of lipid.
Iodine solution for starch
Benedict’s solution for glucose and waterbath
Biuret reagent for protein
Ethanol & water (emulsion test) for lipids
A colour chart can be used to make more accurate comparisons
A colorimeter can be used to give very accurate values for colour.
Starch = blue-black with iodine.
Glucose = brick red with Benedict’s (after heating).
Protein = purple with Biuret.
Lipid = cloudy white emulsion.
Solid food should be ground and mixed with a small amount of water.
Add iodine to food → starch test.
Add Benedict’s, heat in water bath → sugar test.
Add Biuret → protein test.
Mix with ethanol then water → lipid test.
Record colour changes.