Categories
Biochemistry

Crocus chemistry: Saffron, colours, and poisonous imposters

Infographic on the chemistry of crocuses. Crocus stigmas are yellow due to carotenoid pigments and related compounds. One of these compounds, crocin, causes the deep red colour of the stigma of Crocus sativus, from which the spice saffron is produced. The orange and yellow petals of crocuses also owe their colours to carotenoids. Purples are due to anthocyanin pigments, commonly glucosides of delphinidin and petunidin. Crocus sativus, commonly known as saffron crocus, is also sometimes referred to as the autumn crocus due to when it flowers. However, "autumn crocus" is also used as a name for species in the Colchicum genus. All plants in the Colchicum genus contain the toxic alkaloid colchicine. Ingesting colchicine can lead to multiple organ failure and death. Due to its anti-inflammatory properties, colchicine is used as a treatment for gout.
Click to enlarge

Did you know that saffron is obtained from a type of crocus? This is a fact that had somehow escaped me, and which I only discovered when wondering why saffron contains a compound called ‘crocin’. Turns out that, yes, there is a connection!

While the idea for this infographic was prompted by the eruption of crocuses currently taking place in our garden, these are Crocus vernus, the spring crocus. The crocus from which saffron is obtained is commonly called the saffron crocus, or sometimes the autumn crocus (more on that alternative later). As the latter name suggests, the saffron crocus, Crocus sativus, flowers in the autumn.

Saffron is obtained from the crocus stigmas, three deep red tendrils protruding from the centre of each flower. It takes a colossal 150 crocus flowers to produce a single gram of dried saffron, which goes a long way towards explaining why it’s the most expensive spice on supermarket shelves. Saffron’s deep red colour is due to the presence of crocin, a compound derived from the carotenoid compound crocetin. Crocin and related compounds are found in other crocuses, too, contributing to the range of yellows and oranges.

The purples and lilacs of crocus petals are due to a different group of compounds: anthocyanins. Researchers have identified nine key anthocyanin compounds as contributing to crocus colour, mainly glucosides of delphinidin and petunidin. They also identified some malonated anthocyanins which appear to be completely unique to crocuses.

While the crocus from which saffron is derived is sometimes referred to as “autumn crocus”, this moniker has the potential for deadly confusion. “Autumn crocus” is also commonly used as a name for several species in the Colchicum genus. These plants can look very similar to the saffron crocus, and also flower during the autumn, but you definitely don’t want to harvest any parts of them – all parts of the plant contain the toxic alkaloid colchicine.

Justin Brower over at Nature’s Poisons has a great post on colchicine, where he goes into the mechanism behind its toxicity:

Colchicine has two modes of action in the body.  In the first, colchicine inhibits neutrophil activity.  These are a type of white blood cell that kicks into gear during an immune response, causing inflammation.  […] The second mode of action is by binding to tubulin, which in turn inhibits mitosis […] the process in the cell cycle in which the chromosomes are split into two identical daughter cells.  We need mitosis for growth and replacement.

Colchicine: Don’t Eat the Crocus – Nature’s Poisons

Eating colchicine can lead to all manner of unpleasant symptoms, and more seriously can result in multiple organ failure and death. In short, you really don’t want to get autumn crocuses confused.

Despite its toxicity, colchicine has also been used as a treatment for gout due to its anti-inflammatory properties – usually when patients can’t take more standard anti-inflammatory painkillers. It’s another classic case of the dose making the poison, albeit one where there’s not a huge degree of difference: the dose required for therapeutic effects is not hugely distant from the dose at which toxicity is seen.

The good news is that true crocuses don’t contain colchicine. While eating bits of them still isn’t recommended – they still contain other compounds which, though they may not kill you, are still more than capable of kicking off unpleasant symptoms – saffron itself is safe to eat. Considering how many crocus plants it takes to make it, you’re probably still best off buying it at the supermarket.

The graphic in this article is licensed under a  Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. See the site’s content usage guidelines.

References/further reading