Reagents and food testing

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 .

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

Food sample	Reducing sugar
Reagent	Benedict’s
Method	Add Benedict’s reagent to the food and boil in a water bath.
Initial colour	Blue
Colour of positive result	Brick red precipitate

Food sample	Starch
Reagent	Iodine
Method	Add iodine reagent to the food.
Initial colour	Yellow-brown
Colour of positive result	Blue-black

Food sample	Protein/amino acids
Reagent	Biuret (a mixture of sodium hydroxide and copper sulfate).
Method	Add Biuret reagent to the food.
Initial colour	Blue
Colour of positive result	Lilac/purple

Food sample	Fat
Reagent	Ethanol
Method	Add ethanol to the food to dissolve the fat then add water.
Initial colour	Colourless
Colour of positive result	White emulsion

Nutrition and food tests (CCEA)Reagents and food testing