There are different tests which can be used to detect carbohydrates, proteins and lipids.
They involve adding a reagent to a food sample which changes colour depending on what biological molecules are present.
Sometimes it may be necessary to crush the food or add water to the food before adding the reagent.
|Food sample||Reagent||Method||Initial colour||Colour of positive result|
|Reducing sugar||Benedict’s||Add Benedict’s reagent to the food and boil in a water bath.||Blue||Brick red precipitate|
|Starch||Iodine||Add iodine reagent to the food.||Yellow-brown||Blue-black|
|Protein/amino acids||Biuret (a mixture of sodium hydroxide and copper sulfate).||Add Biuret reagent to the food.||Blue||Lilac/purple|
|Fat||Ethanol||Add ethanol to the food to dissolve the fat then add water.||Colourless||White emulsion|