Particularly striking and important colours are reds and yellows. They are found hidden all over the world: in tulips, eggs, fish... They all have something in common. In this experiment, you can take a look at nature's tricks and discover the secret of her colours.

Let's go - have fun!

Place the funnel in the test tube and line it with filter paper folded several times in the middle. For this purpose, cut the filter paper into a circle.

Then pour the contents of the mortar into the funnel and wait until the solution has run through the filter paper into the test tube.

Unfortunately, this cannot be said exactly, because each of you will get a different amount of filtrate. The filtrate is what remains after filtering. But with the sketch on the left you can estimate approximately how much oil and water you need to add.

Now you can sit back and relax and watch your glass.

Gradually you can observe a so-called phase separation. This means nothing other than that the oil and the water separate again. You may have observed this phenomenon before when making salad dressing.

In your experiment, the oil has taken on a yellow colour and is the upper phase in your test tube. Meanwhile, the water is red. This phase is in the lower part.

Most carotenoids are fat-soluble pigments (dyes). Although they do not all have the same colour, they are grouped together based on their chemical structure (tetraterpenes, from eight isoprene units). They can normally only be newly synthesised (produced) by microorganisms, fungi and plants. Humans and animals, on the other hand, for which carotenoids are also essential for survival, cannot produce them themselves and must ingest them with their food. The only exception is aphids, in which several species have acquired the gene for carotenoid production from fungi. This works thanks to so-called horizontal gene transfer.

Carotenoids criss-cross the food chains. They are responsible for the "yellow in the egg", the redness of koi, goldfish and salmon meat. They are responsible for blue crabs (lobster, shrimp,...) turning red in hot water. They are the reason for the yellow beak of the mallard drakes, which vie for the favour of the ducks (the more yellow the beak, the better the drake looks to the ducks) and many more.

For us humans, beta-carotene is the precursor to provitamin A and is important for our immune system and the visual process, among other things. That's why they say you should always eat your carrots so that you can see better.

Experiment 1:

Crack an organic egg and a conventional egg into a transparent glass and compare the colour of the yolk. Most conventional laying hens are fed so much carotenoid-enriched feed that the yolk appears almost reddish-orange. Organic farms also add carotenoids but rarely to the same extent. If you break open organic eggs from different sources, you will find the most varied shades of yellow.

Experiment 2:

When you have seafood for dinner again, throw a blue shrimp into a transparent glass of hot water. During boiling, you can see that the initially blue animal gradually turns red. The protein component of the blue protein-carotenoid complex denatures (breaks down) and the red carotenoid with the illustrious name astaxanthin becomes visible.