The Kamikaze Chemistry of Carrots

Carotenaemia hand (left) compared with a normal hand http://dermnetnz.org/systemic/carotenaemia.html

Carotenaemia hand (left) compared with a normal hand (right)
(Image: http://dermnetnz.org)

Have you ever had carotonemia? Or know someone who has?

Fear not, it is not fatal or contagious; it is usually just the result of eating too many carotenoids!

As the name suggests, carotenoids are found in carrots and they have an orange colour.

But why do the carotenoids from your carrot-addiction end up in the palms of your hands?

 

Carotenoids belong to a Family of fat-soluble pigments

Safflower oil and water © Sciengist

Safflower oil and water © Sciengist

We all know that oil and water don't mix.

The water stays at the bottom and the oil floats on top.

Well, it depends on something called the Polarity of the molecule.

Basically, if charges are 'out of balance' on a particular molecule, the one end can be more positive than the other end. It is therefore termed to be Polar.

Conversely, if the charges are in balance, the molecule is termed Non-Polar.

It turns out that polar molecules such as water will mix with other polar molecules such as ethanol. Similarly, non-polar ones will mix with other non-polar molecules.

So, some carotenoids are non-polar and your hands have protective fatty (non-polar) pads on the palms and fingers and that's where those excess orange carrot pigments end up.

The Humble Carrot © Sciengist

The Humble Carrot © Sciengist

 

Any scientific term that ends in -oid usually denotes a group of things.

So, the carotenoids is quite a large family of compounds and they are found in surprising places such as bird feathers and all sorts of coloured vegetables and fruit.

There are two types of carotenoids (based on chemical structure): carotenes and xanthopylls.

Lycopene and beta-carotene are examples of carotenes, while lutein, zeaxanthin, and astaxanthin are xanthopyll carotenoids.

 

Carotenoids are important anti-oxidants

The great thing about carotenoids is that they can act as antioxidants in your body.

Interestingly, as they oxidise free radicals and protect your cells, they themselves are destroyed just like the kamikaze pilots of Japan.

Astaxanthin is thought to be one of the best antioxidants of all and it is found in many sea foods: lobsters, salmon, prawns etc. It gives them their deep red colouring but, surprisingly, they don't make it themselves but accumulate it from their diet.

Remember carotenoids are often non-polar molecules; and, as it happens, so is the membrane of every one of your cells. So the carotenoids end up in your cell membranes, just where they can deal with those nasty free radicals.

Phase Separation is a chemical technique which enables the extraction of carotenoids

Home Science Demonstration:

This is an example of a separation process still commonly used by chemists:

Step 1: Grate a carrot © Sciengist

Step 1: Grate a carrot © Sciengist

Step 2: Add it to an oil/water mixture © Sciengist

Step 2: Add it to an oil/water mixture © Sciengist

It is called Phase Separation and, as you can imagine, many different solvents can be used with water (e.g. hexane) to extract compounds with varying polarities.

Step 3: Shake it up into an emulsion © Sciengist

Step 3: Shake it up into an emulsion © Sciengist

Different molecules can have different polar strengths. Some are strongly polar and others have only a weak polarity and they become a little bit uncertain as to which way they will go.

That is why it's probably useful to leave the emulsion on a shaker for a few days. If you don't have a shaker put the bottle on top of the washing machine.

Step 4: Leave it until the oil and water phases have separated again © Sciengist

Step 4: Leave it until the oil and water phases have separated again © Sciengist

Compare the original colour of the safflower oil in the smaller jar (on the left) with the oil phase in the bigger jar (on the right). There they are, dissolved in the oil phase, carotenoids.

DIY Home Experiment

Turn this Demonstration into your own Phase Separation Experiment by grating several carrots, creating several jar solutions and varying the amount of grated carrot you put in each jar.

Can you see a difference in the end results?

What do you think your results are telling you?

Polyethylene chopping boards are stained by fat-soluble pigments in fruit and vegetables

I've scrubbed and scrubbed, but the orange carrot stain is still there © Sciengist

I've scrubbed and scrubbed, but the orange carrot stain is still there © Sciengist

Have you noticed that certain vegetables or fruits leave a stain on your plastic chopping board that is difficult to remove?

That's because the chopping board is made of a non-polar material, polyethylene (PE).

The compound (carotene in this case), also being non-polar, has gone in to the surface of the chopping board quite happily and won't come back out into your soapy water scrub.

Phase Separation can be used to extract all sorts of flavours and colours from common food items.

Common Phase Separations are also conducted in the world of cookery.

People often soak garlic or chillies in olive oil to move their oily components into the oil and add flavour to their dressings and sauces. Items such as, rosemary and citrus peel have oily components which can be usefully extracted into oil too. However, I have often wondered whether those wonderful antioxidants, carotenoids, could not be extracted into olive oil to give colour and flavour as well as offer extra protection against free radicals.

So, here's your edible task:

Try Phase Extractions of: red capsicum, beetroot, rhubarb, blueberries, pumpkin, red or orange flowers or prawn shells

See what you get!

Carotene in prawn exoskeletons (Image: https://everythingneat.wordpress.com)

Carotene in prawn exoskeletons
(Image: https://everythingneat.wordpress.com)

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