I love my naturally-occurring pesticide

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99.99%, by weight, of all the pesticides we consume are naturally-occurring.

That’s a pretty amazing statement, isn’t it? It comes from a paper about dietary pesticides that was published in 1990, and referred to the American diet, but it’s almost certainly still not far from the truth – pesticide use, despite what some of the crazier corners of the internet will tell you – hasn’t increased significantly in the last 26 years. The authors of the paper concluded that “the comparative hazards of synthetic pesticide residues are insignificant” and it’s a valid point. Many of these natural pesticides – chemicals which plants use to defend themselves – have never been fully tested, and some of them are actually well-known toxins.

Plants have been on this planet for a very long time, 700 million years give or take, which means they’ve had an awful lot of time to evolve defences. Some of these are physical, like thorns or spines, but chemistry plays a key role.

For example, one of the most common toxins is solanine. It turns up in potatoes which, as any good gardener will tell you, are part of the nightshade family. Yep, like deadly nightshade. But don’t panic, it’s mostly in the parts of the plant we don’t eat, namely the leaves and stems, with only very small amounts found in the skin and virtually none in the flesh.

DO NOT EAT!

DO NOT EAT THESE!

Unless, that is, your potatoes are exposed to light. Then the tubers start producing lots of extra solanine (and another alkaloid called chaconine), as a defence to stop the uncovered tuber from being eaten. At the same time, they produce extra chlorophyll, which causes them to turn green. The chlorophyll is harmless, but the solanine most definitely is not. It causes vomiting and diarrhoea, and can even be fatal – although this is really only a risk for people who are undernourished. Still, if your potatoes have turned green its safest to throw them out, since cooking doesn’t break the toxins down. Even if they’re not green, if they have a bitter taste it’s safest to get rid of them if you don’t want to risk an extended visit to the porcelain throne.

But solanine is just the tip of the lettuce. Capsaicin (the stuff in chillies) also evolved as a defence mechanism to repel and kill insects, and there’s evidence that it may be carcinogenic under some circumstances. 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) is another chemical which is found in corn, wheat, rye and other grasses and which has been shown to cause carcinogenic changes in human cell lines. Then there are all the various substances in herbs and spices, such as tetradecanoic acid in nutmegpulegone in peppermint, carvacrol in oregano and eugenol in cloves, nutmeg and basil.

But not to panic. None of these chemicals are dangerous in the quantities that we usually consume them. And neither, while we’re here, are the really teeny, tiny amounts of synthetic pesticides that we might be exposed to. So just relax and eat your greens. Well, not if they’re potatoes. You know what I mean.

Anyway, there’s one substance I haven’t mentioned yet, and it’s a biggie – it’s something most of us consume on a regular basis. In fact, it might be the source of over a gram of naturally-occurring pesticide a day, and few of us even give it a thought.

What is it? Coffee. Yes, your daily dose of americano is a veritable cocktail of chemicals. As the dietary pesticides paper points out, “13 g of roasted coffee per person per day contains about 765 mg of chlorogenic acid, neochlorogenic acid, caffeic acid, and caffeine.” A single espresso shot uses about 8 grams of ground coffee, so a mere two shots will take you up to best part of a gram of chemically-goodness, and who restrains themselves to two shots a day?

But there’s good news. Some of these substances could actually be beneficial. Chlorogenic acid appears to moderately lower blood pressureNeochlorogenic acid might actually help to prevent certain cancers, as might caffeic acid (although results are mixed in this case).

caffeine

The world’s most widely-consumed psychoactive drug.

And then, of course, there’s caffeine itself – the world’s most widely consumed psychoactive drug. It has umpteen (technical term) effects not the body, both positive and negative, the most famous being its ability to keep us alert and awake. It’s performance-enhancing and its use was at one point restricted for Olympic athletes, until 2004 when officials decided to remove those restrictions – presumably because they were proving impossible to enforce.

But caffeine didn’t evolve for the convenience of humans, although we have, of course, played our part in farming and selectively-breeding plants. No, it originally evolved to paralyse and kill predator insects. Basically, to stop the plant being eaten which, from the plant’s point of view, is quite important. Interestingly, there’s evidence that it evolved separately in coffee, tea and cacao, suggesting it really is a pretty advantageous thing for a plant to make. But in case you’re wondering, it’s broken down by UV light, which explains why it’s not used as an insecticide spray on other plants.

So, if you’re worrying about pesticides with a cup of coffee in your hand, you can stop. You’re probably consuming more pesticide, daily, than you will get from carrots in your lifetime. Drink up!


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Do you love your naturally-occurring pesticide?

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The chemistry of chocolate

A lot of people believe there’s a deep religious significance to the holiday we’re enjoying right now.  Others argue it’s older than that: an ancient spring festival, celebrating the spring equinox, fertility and new growth.

funny-chocolate-Periodic-Table-chemistryBut every child knows what Easter is really all about.  Yes.  Chocolate.  Yummy, delicious chocolate.

So with that in mind, let’s talk a little about the chemistry of chocolate.  For it is very interesting stuff.  What’s in the lovely, creamy, sweet brown stuff?  And how do they get it to melt so perfectly in your mouth?  And does it really give you a happy high?

How do they get chocolate to melt so perfectly at body temperature?  There is more to this than you might imagine.  First of all you have to know something about crystals.  Most people, upon hearing the word crystals, think about clear, shiny things twinkling from from Katie Price’s latest wedding dress.  But in fact lots of substances form crystals, because a crystal is just a piece of any solid material that has regular shapes arranged symmetrically.  Crystals don’t have to be transparent.  Metals are crystalline.  Pure iodine forms rather pretty grey-silver crystals.  And, crucially, fat also crystallises.

In fact the fat in chocolate, cocoa butter, can crystallise in many different forms.  Only one of these is the lovely, hard, shiny one that is so nice and snappy at room temperature.  If you’ve ever cooked with chocolate, or indeed just left it in the car on a hot day by accident, you probably know that if you melt it and then just let it solidify again the result is dull-looking and crumbly.  Getting the right form of chocolate crystals to form is called tempering, and it’s a complicated business.  First the chocolate has to be melted at a high enough temperature to melt all the crystals.  Then it needs to be cooled to just the right temperature for the best crystals to grow, then agitated, then warmed up a tiny bit (but not too much), then cooled again.  There are other methods, but this is the one that’s used in the big chocolate factories.  Just ask the Oompa Loompas.

This ideal fat crystal form not only looks good and snaps nicely, it also melts at 34 oC.  Normal body temperature is actually around 36 oC, with the oft-quoted 37 oC actually being a tad on the high side.  Skin temperature, on the other hand (geddit?), is somewhere between 32-35 oC depending on how warm the environment is.  This means that chocolate will just about stay solid in your fingers if you don’t hold it too long, but put it in your mouth and the temperature is just right to melt it perfectly, releasing delicious sweetness, creamy fats and other chemicals that stimulate your tastebuds and give chocolate its flavour (craving your easter eggs yet?)

What about the other question: does chocolate really give you a ‘happy high’?  Well, it turns out there’s a whole cocktail of naturally-occurring bioactive chemicals (some people see ‘natural chemicals’ as a bit of an oxymoron and that’s ironic in a way, since the very brain that learned big words like oxymoron is actually stuffed full of natural chemicals that make it work) in chocolate.  Firstly, caffeine, otherwise known its less tongue-tripping name of 1,3,7-trimethylxanthine, but we’ll stick to caffeine.

We’re all familiar with caffeine from tea and coffee, and that drink that’s falsely advertised as giving you wings, but its presence in chocolate is sometimes forgotten.  It is of course a stimulant, exciting the central nervous system (it’s very excitable), boosting heart rate and contracting muscles.  It also acts on receptors in the brain and causes them to release pleasure-producing chemicals.  There isn’t a lot in chocolate though: it varies by type but even in the darkest of dark chocolate, there’s generally less caffeine than you’d get from even a single cup of tea.  Milk chocolate has even less and white chocolate has none at all.

But there’s more of another chemical, also a stimulant: theobromine.  This is interesting stuff.  It’s a heart stimulant and, like caffeine, a diuretic (it makes you wee).  More recently it’s use as a potential treatment for cancer tumours has been investigated.  There is roughly eight times more theobromine in chocolate than caffeine, but we metabolise it quickly so it doesn’t hang around in our bodies for long.  It’s less safe for animals: as any responsible dog owner will tell you, chocolate is very bad for dogs.  This is mostly due to the theobromine (the caffeine isn’t great either, but there’s not so much of that).  If your pooch gets into your Easter eggs, they could suffer nausea and vomiting, diarrhea, muscle tremors and, potentially, heart failure.  So keep your eggs out of reach.

It’s not just stimulants.  Chocolate also contains fatty acids called cannabinoids.  Guess what they’re similar to?  The clue is in the name… yes, their cousin is called tetrahydrocannabinol, and it’s found in the cannabis plant.  When cannabinoids hit the brain they make you feel relaxed and intoxicated.  And that’s not all, chocolate also contains phenethylamine, sometimes dubbed ‘the love drug’ because levels increase in the body when you’re feeling romantic.  Although there isn’t much and it’s metabolised too quickly to  have a significant effect.

So with this delicious swirly mixture of stimulants and suppressants, surely chocolate ought to be on some sort of controlled drug list?  Well, no.  All of these chemicals are present in relatively small amounts, and have a limited effect on the body (human bodies anyway).  People who suffer chocolate cravings aren’t satisfied by just swallowing capsules that contain the relevant chemical compounds, but eating white chocolate – which contains no cocoa solids and therefore none of the psychoactive ingredients – does the trick.  This suggests that the real reason we like chocolate is simply the same reason we like cream cakes: lots of sugar and fat – yummy!

So now you’ve stuffed your brain full of sciencey-stuff, go ahead and stuff your mouth with lots of yummy chocolate.  Happy Easter!

P.S. have you noticed that it’s kem-is-try but cho-ko-late?  This alliteration spoiling bit of linguistics is because the word chemistry derives from the word alchemy, which (probably, people argue over these things) comes from the ancient Egyptian name for Egypt – khem or khame, or khmi.  Hence al-khmi, ‘the Egyptian art’.