Cucurbitacin

Not all bitterness is bad

I’ll be taking a break from writing for a while after this post, need to recharge and avoid any burn out.

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In a previous post, I ricocheted off my love of Bitter Melons (Mormodica charantia) into a minor tangent about naturally bitter compounds.

Cold temperate Bitter Melons

This post will go into more detail about the specific bitter compounds in the Cucurbit or Gourd family (Cucurbitaceae). These bitter compounds are, unsurprisingly, called Cucurbitacins.

I decided to write this article because I have seen some fairly simplistic and some factually incorrect “internet knowledge” about the bitterness of cucurbits. On my quest to understand Bitter Melons more deeply, I side-stepped into cucurbitacins and it seems only fair that I write down what I have gleaned from reading a fair few scientific papers on the topic.

Let’s lay down some facts - pardon the bullet points, this is a fact heavy article.

The toxic Cucurbitacin D, just one of the cocktail of cucurbitacin produced by the generally toxic squirting cucumber (Ecballium elaterium)

Cucurbiticans in General

• Most (or all) cucurbits naturally produce cucurbitacins.

• Cucurbitacins are generally created “in-situ”, which is really a fancy way to say that they are not transmitted around the plant body via sap (unlike tomatoes and solanine).

• Different Cucurbitaceae species, and cultivars within species, produce different levels of cucurbitacins

• Cucurbits produce cucurbitacin as an adaptation to environment stressors, such as drought or pest pressure

  • This likely explains why wild variants with higher cucurbitacin content are more successful than their pampered descendants

Cucurbiticans in Depth

• There are at least 26 different groups of cucurbitacin, and scientists have thankfully chosen to name them alphabetically, starting from A through to T, such as Cucurbitacin B.

• Within this large group, we have safer and less safe sub groups.

• The cucurbitacin groups have not been equally well studied, so you will often see scientists do the equivalent of throwing their hands up in the air.

• Yes, cucurbitacin was investigated as a treatment for COVID-19

Safer and Less Safe Cucurbitacins

• Cucurbitacin C, D, E, & I are pretty nasty and should be avoided

• Occasionally you will read in the press that a person has died from eating a cucurbit

  • One theory is that under certain environmental stressors (heat and drought, and others) the cucurbit will spontaneously re-express the genes that produce large amounts of unsafe Cucurbitacin. In the case of zuchinnis (courgettes), E and I are produced in large amounts. You don’t need to eat much of these two groups to poison yourself.

• Probably the most hardy cucurbit is Ecballium elaterium (squirting cucumber or exploding cucumber) which can withstand ridiculously cold temperatures down to -40°C

• Unfortunately for us, Ecballium elaterium produces a whole cocktail of safe and unsafe cucurbitacins (B, D, E, I, L, and R).

Momordicosides

• Bitter Melon contain a unique Cucurbitacin called Momordicosides which has the same basic chemical shape but with part swapped out for another.

• Momordicosides are probably only found in Bitter Melons. There are at least 9 forms of Momordicoside, and they are generally named alphabetically in the same manner as the cucurbitacins.

  • For example, momordicoside A is just cucurbitacin A but with one part swapped for another.

• Momordicosides are not thought to be as dangerous as Cucurbitacins. This seems reasonable and is regularly tested by their regular consumption in (non-western) human society

So what?

Take some time to unplug that USB drive from your brain, that is a lot of facts to digest in your grey matter.

If there’s any summation you take away from this article, I think it should be this:

Humanity domesticated cucurbits by selectively choosing the least bitter pulps. Decreasing bitterness unfortunately leads to greater pest pressure and weaker climate adaptation.

If we consider the Bitter Melon, it’s an interesting conundrum because that has stayed bitter. People groups have figured out that this bitterness is fine and healthy, but that other bitterness is dangerous.

For plant breeders, you should be mindful that any crosses you make between wild cucurbits and domestic versions risk bringing in complex pathways of dangerously toxic forms of cucurbitacin which you’ll struggle to remove. Before you begin any of these crosses, you should research the scientific journals for chemical breakdowns of the wild cucurbit you want as a parent. If you see the presence of the toxic cucurbitacin group then think twice. I’m told that Joseph Lofthouse almost lost a cucurbit landrace by introducing a bitter cucurbit into his grex.

If in doubt, just breed the plant until there is no bitterness remaining, but bear in mind that nature is rarely completely tamed and can pull a fast one on you (like the deadly reverted zucchinis).

Luckily for me, the Bitter Melon has a great collection of healthy cucurbitacin. This is a double edged blade because I won’t be able to distinguish any deadly bitterness if it creeps in somehow from a rogue cucurbit.

Nature should always be respected.

Until next time.

References

• Intense Bitterness in Commercial Zucchini, page 83

• Photosynthetic response of bottle gourd [Lagenaria siceraria (Molina) Standl.] to drought stress: Relationship between cucurbitacins accumulation and drought tolerance

• Cucurbitacins – An insight into medicinal leads from nature

• Wikipedia article that cites the 9 momoridiosides

• Recent Advances in Momordica charantia: Functional Components and Biological Activities

• Cold Tolerance in the Cucurbitaceae

• A list of known Cucurbitacin groups and cucurbits that naturally produce them

• Evaluation of Antioxidant, Antibacterial and Cytotoxic Activity of Methanol Extract from Leaves and Fruits of Iranian Squirting Cucumber (Ecballium elaterium (L.) A. Rich)

• Plausible mechanisms explaining the role of cucurbitacins as potential therapeutic drugs against coronavirus 2019

• Origin and domestication of Cucurbitaceae crops: insights from phylogenies, genomics and archaeology

Images

• Photo of squirting cucumber, Ecballium elaterum

• Cucurbitacin D diagram