Food tests (core practical): Key concepts in biology: Biology: GCSE (9:1)

Qualitative reagent

A substance used in chemical analysis to test for the presence of specific molecules

Qualitative

Relates to measuring the quality of something rather than its quantity

Benedict's reagent

When heated will turn from blue to a brick-red precipitate in the presence of reducing sugars

Results for Benedict's reagent

The solution will change from blue to green to yellow to brick-red depending on the level of reducing sugars present

Biuret reagent

Turns from blue to lilac/purple in the presence of proteins

Iodine test

Turns from yellow-brown or orange to blue-black in the presence of starch

Ethanol and water

When shaken will turn from colourless to a milky-white emulsion in the presence of lipids

Sudan III

When shaken will turn from brick-red to a red-stained oil layer in the presence of lipids

Carbohydrates

Provide energy for chemical reactions and can break down into sugars

Reducing sugars

A sugar such as glucose or fructose that can act as a reducing agent

Lipids

An energy store of fats and oils that can break down into glycerol and fatty acids

Proteins

The building blocks of cells and tissues that can break down into amino acids

Precipitate

Deposits of solid in a solution

Mortar and pestle

Devices used for crushing and grinding up food substances

Water bath

A container of water heated to a given temperature for control purposes

Positive result

A result that shows the presence of a specific substance

Negative result

A result that does not show the presence of a specific substance