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	��Ա�徱��’s	Add ��Ա�徱��’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	��Ա�徱��’s
Method	Add ��Ա�徱��’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

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