Authorised food colourings include:
natural food colourings, available as concentrates from plants or from their juices and that have not undergone any chemical extraction process;
artificial food colourings with no natural equivalents;
industrially-synthesised products, even where natural equivalents exist.
Highlighting the natural colourings in some plants
Put some finely chopped red cabbage in a 250 ml beaker.
Add some water, stir and leave to stand for 10 minutes.
Filter and stir again.
Divide the red cabbage filtrate between three (Erlenmeyer) titration flasks:
- Add nothing to the first flask.
- Add lemon juice to the second flask.
- Add some egg white to the third flask.
How can obtain three different colours from a single plant?
You can get several different colours from the same colouring substance depending on its concentration, the environment in which it is used and the presence of other colouring agents.
Red cabbage contains colourings that change colour depending on the ambient pH:
- Red cabbage juice turns pink in an acidic environment (with lemon juice).
- Red cabbage juice turns green in an alkaline environment (with egg white).