Food Chemistry Basics: Everything You Need to Know About Turmeric
Turmeric is a distinct and easily recognisable spice with a bright yellow colour and unique flavour and smell. Long a traditional and key ingredient in Indian curries, turmeric has gained popularity in the health food and plant-based space. This is due not only to its colour and taste, but also for its health benefits.
While turmeric’s colour is stable and long lasting, it is also changeable. Through different chemical processes, turmeric can be transformed into a variety of different colours.
Whether the goal is to create the perfect curry or develop an exciting custom spice blend, turmeric is a powerful ingredient that should not be overlooked.
Turmeric (and ginger) belong to the Zingiberaceae family of plants. With these plants, the spice is harvested from its mass of roots growing within the soil. These underground stems are called the rhizome.
In the case of turmeric, the exterior of the tuber is rough and a yellow-brown colour. The inside is a bright yellow or orange, due to the presence of the chemical curcumin.
How is turmeric powder made?
It is the brightly coloured interior of the tuber that becomes turmeric powder.
First, the rhizome (the underground mass of roots) is harvested, and then boiled or steamed. After it has been sufficiently cooked, the tubers are dried until only 8%–10% moisture remains. While this process was traditionally accomplished using the powers of the sun, modern times have seen a shift to industrial methods.
The next step is polishing, which removes the rough exterior and leaves only the vibrant insides. What remains of the root is then ground down into the powder that we know as turmeric.
Turmeric owes its distinctive colour to an assortment of molecules called curcuminoids. Curcumin, demethoxycurcumin, and bisdemethoxycurcumin are the three most common types of curcuminoids found in turmeric, with its bright hue mainly a result of the curcumin. In total, 5%–6.5% of turmeric is actually made of curcuminoids. More than half of that is pure curcumin.
When dry, curcumin is a stable molecule and retains its colour extremely well over large amounts of time. Several years can pass and a jar of turmeric will still be just as bright as it was the day it was purchased. However, the aroma (created by the presence of turmerone, ar-turmerone, and zingiberene molecules) is not as stable and will fade over time. The flavour will also wane.
The molecule curcumin is made up of several rings and double bonds, which is common for coloured molecules. These rings and bonds capture light, hence the bright colour that we perceive with our eyes.
As curcuminoids only account for 6.5% of turmeric’s total components, what else is the tuber made of? About 70% of the root are carbohydrates, giving the turmeric its structure. This is common in all plants, which are naturally high in carbohydrates.
Water, fats, proteins, and volatile oils can also be found in turmeric powder.
Under the right conditions, turmeric can actually turn fluorescent. If turmeric is sprinkled into an alcohol (like vodka), as a UV flashlight shines on it, the turmeric will emit a bright yellow-green glow as it floats to the bottom of the liquid. This is due to that incredible molecule: curcumin.
As it falls, the curcumin absorbs the UV light coming from the flashlight. The curcumin’s electrons, now containing the UV energy, are elevated from a ground state to an excited state brought on by the higher level of energy. This heightened energy is soon lost due the vibrations of the electrons, which quickly drop back to their ground state. The excess energy is given off as visible light, thus producing a fluorescent effect.
The chemical structure of curcumin is sensitive to alkaline, and changes depending on the pH value of its environment. When curcumin is in an acidic environment, it retains its vivid yellow hue. When exposed to alkaline conditions, curcumin will change its colour to become a dark red. This shift requires a pH of 8 or above.
The transition from yellow to red is caused by a change in the chemical structure of the curcumin molecule brought on by the surrounding alkaline. The length of the alternating single and double bonds between curcumin’s atoms determines which wavelengths of light will be absorbed by the compound. If the length is changed, so is turmeric’s colour.
Alkaline solution has the ability to alter the chemical structure of curcumin. The length is altered, resulting in different wavelengths being absorbed, which then produces a red colour instead of yellow.
Curcumin in the Body
Human bodies do not absorb curcumin well when consumed orally. The compound (which makes up only 3% of turmeric) is poorly absorbed, rapidly metabolised, and quickly eliminated. Its lack of bioavailability means that despite the lauded health benefits, curcumin has not performed well in clinical trials with humans.
Curcumin has had mixed results in animal and laboratory studies. Some of these studies have suggested that turmeric can have anti-inflammatory and anti-cancer effects, thus leading to the belief that turmeric is a powerful healing tool. Unfortunately, these claims have failed to hold up in double-blinded and placebo-controlled clinical trials.
With its distinctive colour, smell, and taste, turmeric is a powerful addition to both recipes and spice blends. It has long been harvested for Indian curries, transforming the underground roots of the turmeric plant into a vivid yellow powder.
Its bright and recognizable yellow-orange colour is a result of the chemical curcumin, which makes up 3% of the root’s compounds. As it is a stable molecule, curcumin retains its hue even through large amounts of time. While the aroma and flavour will fade over time, the enduring colour can still add a lively pop to dishes.
Curcumin also holds the potential to change colour, particularly in alkaline environments. When exposed to alkaline, the yellow curcumin shifts into a deep red, meaning that it can be a surprising and exciting ingredient.
While turmeric’s health claims have failed to hold up in clinical trials due to its poor bioavailability, this popular spice brings a unique colour and taste to the kitchen.
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