Infographic on the chemistry of turmeric. Turmeric fluoresces under UV light with a yellow-green glow. Curcumin gives turmeric its yellow colour and is also responsible for this fluorescence, due to excitation of electrons in its molecules which then emit light as they fall back to the ground state. Curcumin also causes the colour of turmeric to be pH sensitive due to subtle changes in its structure. Health effects of turmeric have been hypothesised but are unconfirmed in humans, and poor absorption of turmeric by our digestive systems makes substantial health benefits unlikely.
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If you’ve ever made a curry, you’ve likely used turmeric – you may even have some in your kitchen right now. It’s probably not the first thing that comes to mind when you think about doing chemistry, but there are actually some pretty neat chemistry tricks you can do with it! In this post, we take a look at these, as well as the plethora of health benefits commonly attributed to the yellow spice.

Tumeric is a plant that’s a member of the same plant family as ginger. Like ginger, it’s the rhizomes of the plant (the underground stems) that are used to make the spice. As with all spices, turmeric is a mix of chemical compounds, but its bright yellow colour is due to the presence of a particular compound: curcumin. This compound is also behind some neat chemistry that you can easily try out for yourself.

Two Tumeric Tricks

The first thing you can do with turmeric is make it fluoresce. To do this, you only need turmeric, some alcohol (such as vodka), and a UV torch, which you can easily get hold of online. If you place the alcohol in a container, illuminate the container in a darkened room with a UV torch, and then sprinkle in some turmeric, incredible green-yellow glowing trails can be seen as the turmeric falls through the liquid.

This happens because electrons in the curcumin molecules absorb UV light from the UV torch, gaining energy as they do so. This energy promotes them from where they started (what we refer to as the ‘ground state’) to a higher energy level (what we refer to as an ‘excited state’). This doesn’t last long though; they quickly lose some of this energy as vibrational energy, before dropping back down to the ground state, emitting their excess energy as visible light, and giving us the fluorescence seen here.

(Note: You might wonder why alcohol is used rather than just water. This is because turmeric is more soluble in alcohol than water, so the fluorescence is more visible).

There’s more chemistry you can try with turmeric: it can be used as an indicator to help us spot the difference between acids and alkalis. If turmeric is added to an acidic solution, it stays its usual yellow colour. Add it to an alkaline solution, however, and it changes colour from yellow to red.

Curcumin is again the chemical culprit behind this effect. This time, it’s a subtle change in its chemical structure that’s responsible. When it’s added to an alkaline solution, the subtle loss of a hydrogen atom alters the wavelengths of light that it absorbs. This is what causes the colour to change from yellow to red.

Turmeric’s Health Effects

A big deal is made of the supposed health effects that turmeric can have. Simply type ‘turmeric’ into Google (other search engines are available) and you’ll run into an array of articles with titles like “10 turmeric benefits: Superior to medications?”. If you’re here for a short answer, then *SPOILER ALERT* the answer to the question that the article poses is “No”. If you’d like a little more detail, then buckle up.

So what’s the big deal about turmeric and curcumin? Well, it’s been lauded as an effective painkiller, antidepressant, anti-inflammatory, cancer treatment, and maybe even a treatment for Alzheimer’s disease. With all that, you might well wonder why doctors aren’t already prescribing it by the bucketload. Before you start liberally sprinkling turmeric over your breakfast, lunch, and dinner, there are more than a few caveats to what we know about turmeric’s effects.

First of all, it’s important to realise that although a large number of studies have been carried out on turmeric, the vast majority of these are studies carried out on isolated cells or in animals. The effects observed have been mildly promising in cases, including anti-inflammatory and anti-cancer effects, but excitement about this should be tempered. Lots of things work in isolated cells in the lab, but don’t work the same in the human body. Effects in animals can be more promising, but can still fail to manifest in humans.

Positive results in clinical trials (in humans) are key when it comes to identifying effective medicines. Turmeric has been subjected to relatively few of these, and they’ve tended to have mixed results. There’s a very thorough run-down of the science behind turmeric health claims given here by the Linus Pauling Institute. They point out another turmeric limitation:

“In humans, curcumin taken orally is poorly absorbed and rapidly metabolized and eliminated. Therefore, the potential of curcumin as a therapeutic agent is limited by its poor bioavailability“.

Translated into simpler terms, this means that curcumin isn’t very well absorbed when we eat it, and what is absorbed is rapidly broken down and gotten rid of by the body. If you consider that only around 3% of turmeric is curcumin anyway, you start to realise that you’re going to need to be on a serious turmeric binge to absorb amounts of curcumin that might have some kind of effect.

This isn’t to say that turmeric has no health benefits whatsoever, and there are still ongoing clinical trials looking into its potential beneficial uses. However, it does mean that you should probably take that next Daily Mail article you read about how turmeric is going to cure Alzheimer’s/help beat cancer/keep you illness-free forever quite lightly! 

EDIT 11/01/2017: A recent review published in January 2017 suggests that the prospects of curcumin ever making it as an effective drug for any condition are slim. The review points out that “No double-blinded, placebo controlled clinical trial of curcumin has been successful”, and concludes “curcumin is an unstable, reactive, non-bioavailable compound and, therefore, a highly improbable lead”. The full review can be read here.

Update 06/08/2023: In updating this graphic, I’ve also updated the section about the pH colour change of turmeric. This previously referred to keto-enol tautomerism of curcumin as responsible for the colour change, but a reader email has highlighted that, though this is widely written about, it’s actually incorrect. The colour change is actually the result of a switch from an enol to a deprotonated enol form. I’ve updated the structures in the graphic accordingly. There’s more detail on these structures here.

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References & Further Reading