Curcumin
Also written curcuminoids, curcumin (curcuminoid), curcuminoid
Quick answer
The yellow pigment of turmeric, the most-studied compound in the spice cupboard, and the clearest case anywhere of laboratory findings being reported as though they were clinical ones.
What it does
Curcumin is responsible for turmeric’s colour and for a good part of its bitterness; it contributes almost nothing to the aroma, which comes from a separate volatile fraction dominated by turmerone. That split is why turmeric behaves as it does in a dish — the colour and the bitterness arrive together and stay, while the earthy, faintly gingery smell fades. It is an intensely strong colourant, staining plastic, worktops and fingers at concentrations far below those needed to flavour anything, which is a practical fact about cooking with it and the reason it is used industrially as a food colour.
How it behaves when cooked
Four properties of the molecule, and what they mean at the stove.
- Volatility
- low
- Fat solubility
- moderate
- Water solubility
- low
- Heat stability
- moderate
Curcumin is poorly soluble in water and much better in fat, which is the reason every tradition that uses turmeric seriously cooks it in oil at the start of the dish rather than stirring it into liquid. Turmeric added to a watery stew stays as suspended particles and tastes raw and chalky; the same turmeric bloomed in hot fat for thirty seconds disperses, loses its rawness and colours the whole dish evenly. It needs that heat — raw turmeric powder has a distinctly unpleasant dusty bitterness that cooking removes — but not much of it, since prolonged high heat degrades the pigment and turns a bright yellow dish brownish. It is also markedly sensitive to light and mildly pH-responsive, shifting towards red in alkaline conditions, which occasionally surprises people baking with it and bicarbonate of soda together.
Spices that carry it
Recorded on the compound rather than on each spice, so the two cannot disagree.
- TurmericPrincipal component
What cooking and processing were measured to do to it
Findings from studies in which this compound was followed through heat, fat, water, drying or storage. Each belongs to its study and its conditions.
Simmering and boiling · Decreases Curcumin
Turmeric boiled for 10 or 20 min, or pressure cooked for 10 min, lost between 27 and 53 per cent of its curcumin, the largest loss coming from pressure cooking. Cooking it together with red gram (pigeon pea) made no difference to the loss.
Conditions: in water · Boiling for 10 or 20 min; pressure cooking for 10 min · Turmeric alone and with red gram; curcumin measured by HPLC after freeze-drying
Curcumin is not indestructible in a wet dish: a simmered or pressure-cooked dal keeps part of its curcumin, not all of it. The study measured the compound, and says nothing about how the colour of the dish looked.
What this does not show: Read in the abstract only. One laboratory, and the abstract does not give the variety of turmeric, the amount of water or the loss for each treatment separately. Curcumin was measured in a solvent extract of the freeze-dried cooked spice.
Measured on the spice
Acid and alkali · Retains Curcumin
Cooked in the presence of tamarind, turmeric lost 12 to 30 per cent of its curcumin, against 27 to 53 per cent when it was boiled or pressure cooked without it.
Conditions: in acid · Boiling for 10 or 20 min; pressure cooking for 10 min · Turmeric cooked in the presence of tamarind, a sour ingredient
The smaller loss with a sour ingredient is consistent with curcumin being more stable in acid than in neutral or alkaline water, which solution studies show independently.
What this does not show: Read in the abstract only. The pH of the cooking liquid is not given, so the protection cannot be attributed to acidity on this evidence alone; tamarind brings other substances besides acid.
Measured on the spice
Simmering and boiling · Converts Curcumin, Ferulic acid, Vanillin, Vanillic acid
When curcumin is degraded by the heat of domestic cooking, the three major products are ferulic acid, vanillin and vanillic acid. The molecule breaks at the diketone bridge that joins its two halves, and at the first carbon of the chain linking the two aromatic rings.
Conditions: Heat treatment of the kind met in domestic cooking; products isolated by LC
What this does not show: Read in the abstract only, which does not state the conditions or the yield of each product. Identifying the products says nothing about whether they can be tasted or smelled in a dish.
Measured on the pure compound
Acid and alkali · Decreases Curcumin, Vanillin, Ferulic acid, Feruloyl methane
Pure curcumin dissolved in phosphate buffer at pH 7.2 and 37 °C was about 90 per cent decomposed within 30 min. Across pH 3 to 10 the breakdown was pH-dependent and faster under neutral and basic conditions than in acid. Vanillin, ferulic acid and feruloyl methane were identified as minor products, and vanillin increased with time.
Conditions: in water · 37 °C · pH 3 to 10; the figure quoted is for pH 7.2 · Pure curcumin in 0.1 M phosphate buffer
What this does not show: Read in the abstract only. Curcumin dissolved in a buffer is far more exposed than curcumin held inside turmeric particles, starch and fat in a dish; the same abstract reports much slower breakdown in media containing serum. A pharmaceutical study at body temperature.
Measured on the pure compound
Acid and alkali · Decreases Curcumin, Demethoxycurcumin, Bisdemethoxycurcumin
In aqueous solution the three turmeric pigments broke down faster as the solution became more alkaline, the rate rising steeply from pH 7.45 to a maximum at about pH 10.2. The half-lives of curcumin, demethoxycurcumin and bisdemethoxycurcumin were 900, 1700 and 2200 h at pH 7.45, and 0.4, 1.0 and 5.0 h at pH 10.2. Bisdemethoxycurcumin was the most resistant of the three.
Conditions: in alkali · pH 7.45 to above 10.2 · Purified pigments and commercial oleoresin in aqueous solution
An alkaline ingredient such as bicarbonate of soda is the condition under which turmeric colour is least stable. The figures are for pigment in solution and should not be read as the life of the colour in a batter or a dough.
What this does not show: Read in the abstract only, which does not state the temperature. Its half-life at pH 7.45 is very much longer than the breakdown another solution study reports near the same pH at 37 °C; the two used different media and cannot be reconciled from their abstracts.
Measured on the pure compound
Toasting and dry roasting · Decreases Curcumin
Thermogravimetric analysis of curcumin showed decomposition in two stages, and led the authors to conclude that where curcumin is used as a food colouring the processing temperature should not exceed 190 °C.
Conditions: in air · Heated progressively in a thermogravimetric instrument · Pure curcumin as used for food colouring
What this does not show: Read in the abstract only. The pure pigment heated dry in an instrument, with loss of mass as the measure; chemical change that does not release volatile products would not be seen. It is not a measurement of turmeric in a pan or an oven.
Measured on the pure compound
Frying and blooming in fat · Converts Curcumin, Deketene curcumin
Curcumin heated to the point of pyrolysis, alone or in coconut fat or olive oil, gave a number of more hydrophilic isomers and decomposition products. One of them was identified by NMR as deketene curcumin, a compound previously known only as a synthetic derivative.
Conditions: in oil or fat · Curcumin pyrolysed with and without coconut fat or olive oil; products followed by HPLC
What this does not show: Read in the abstract only, which gives neither the temperature nor the yield. It establishes that curcumin is chemically altered by strong heating in fat, not how much survives ordinary frying.
Measured on the pure compound
Steaming · Depends on conditions Curcumin, colour
A mobile steam vessel built to cook turmeric before drying brought the cooking time to 10 min, against 15 min in a parboiling drum and 25 min by the open steaming that the authors describe as farmers’ practice. The design aim was to retain as much curcumin as possible while shortening the cook. Rhizomes cooked in the vessel gave colour values of L 53.74, a 58.46 and b 18.16.
Conditions: in steam · 10 min in the new vessel; 15 min in a parboiling drum; 25 min by open steaming · A wheeled steam vessel holding 100 kg of rhizomes
What this does not show: Read in the abstract only, which states the aim of retaining curcumin but gives no curcumin figures and no colour values for the other two methods. An equipment paper from one group.
Measured on the spice
Blanching · Increases Curcumin, polyphenol oxidase, peroxidase, drying time, enzyme activity
Blanching turmeric by a combined hot-air and microwave method before drying shortened the drying time by between 6.35 and 34.92 per cent, depending on how long the blanching lasted. Polyphenol oxidase was entirely inactivated after 8 min and peroxidase after 10 min. At 8 min, the dried turmeric held 20.76 per cent more curcumin than turmeric dried without blanching.
Conditions: 0 to 10 min; best result at 8 min · Hot-air microwave rolling blanching, followed by drying
The measurement fits the reasons producers give for cooking turmeric before drying: the heat stops the browning enzymes and the rhizome then dries faster.
What this does not show: Read in the abstract only. A novel blanching machine, not the boiling or steaming used on farms. “More curcumin” is relative to unblanched dried turmeric in the same study.
Measured on the spice
Drying · Depends on conditions Curcumin, colour
Of six drying methods applied to the same sliced turmeric, freeze-drying and microwave drying left the most curcumin, 3.8 per cent, and sun-drying the least, 2.6 per cent. Colour followed the same order: the freeze-dried powder was the lightest and yellowest (L* 74.0, b* 63.8, browning index 17.07), the sun-dried the darkest and reddest (L* 48.7, b* 51.0, browning index 36.3), and the oven, vacuum, infrared and microwave samples did not differ significantly from one another in browning. Yellowness and chroma correlated strongly with curcumin content (r = 0.92). The authors attribute the poor result in the sun to light, heat and oxygen acting together over a long drying time.
Conditions: in air · Sun at 30 to 35 °C against oven, vacuum, infrared, microwave and freeze-drying · Unboiled slices 3 mm thick
What this does not show: Unboiled slices of hydroponically grown turmeric; commercial turmeric is boiled before drying, which changes how the pigment is distributed. One trial, three replicates. The explanation offered for the sun-dried result was not tested.
Measured on the spice
Drying · Depends on conditions Curcumin, demethoxycurcumin, bisdemethoxycurcumin, colour
Under simulated sunlight, the turmeric that lost curcumin was the turmeric that dried slowly. At 40 °C curcumin fell significantly under both covers, from 197.03 to 182.50 mg/g of dry solids under the UV-blocking cover and from 211.97 to 184.99 mg/g under the UV-transmitting one, and total curcuminoids fell with it. At 50 and 70 °C the changes were not significant, and at 70 °C under the UV-blocking cover no curcuminoid was lost. The authors relate the losses to the accumulated heat load, which was highest in the longest runs. The powder dried at 70 °C was nonetheless the darkest, with the lowest lightness and yellowness under both covers.
Conditions: in air · 40 to 70 °C under simulated sunlight · UV-blocking polycarbonate or UV-transmitting acrylic cover; curcuminoids before and after drying
In this experiment a quick, hotter drying protected the pigment better than a long, cool one in the light, at some cost to the brightness of the powder.
What this does not show: Thin unboiled slices under lamps. The fresh samples for each run differed in curcuminoid content, so each comparison is within a run. One significant loss was also recorded at 60 °C under the UV-blocking cover, which does not fit the trend neatly.
Measured on the spice
Storage · Decreases Curcumin, demethoxycurcumin, bisdemethoxycurcumin, colour, antioxidant capacity
Turmeric oleoresin exposed to ordinary fluorescent light or to white LED light lost colour and fluorescence significantly, and the white LED caused the greater instability. Each of the three curcuminoids decreased, with curcumin degrading the fastest under both lamps. The authors conclude that the instability of turmeric pigment under common lighting should be taken into account when turmeric-containing products are processed, stored and distributed.
Conditions: Fluorescent light and white LED, both at 10 W/m², against dark storage
What this does not show: Read in the abstract only, which gives no rates or exposure times. The material was an oleoresin, in which the pigment is far more exposed to light than inside particles of ground rhizome.
Measured on the spice
Not to be confused with
Compounds a reader is likely to take for this one, and why they differ.
Turmerone
The volatile fraction that supplies turmeric’s aroma. Curcumin supplies colour and bitterness and no smell, which is why the health literature about curcumin and the culinary experience of turmeric are largely about different compounds in the same root.
Capsanthin
The other great spice colourant. Capsanthin is red and fat-soluble; curcumin is yellow and barely soluble in anything. Substituting turmeric for paprika to get colour gives the wrong colour and the wrong solubility behaviour at once.
Safety
What the concern is. The dose, the population and the evidence level live on the spice profiles, which is where a reader with that question actually arrives.
Almost the entire clinical literature concerns purified curcuminoids at doses formulated for absorption, frequently with a bioavailability enhancer, at exposures nobody reaches by eating turmeric — curcumin is absorbed poorly enough from food that the gap is not a matter of degree. Reported harms, including liver injury, attach to those concentrated preparations. The turmeric profile records what the evidence supports and what it does not, with the exposure stated on every finding; this note exists so that a reader arriving at the compound does not read the supplement literature as a fact about their curry.
Questions this page answers
- what is curcumin
- what does curcumin do
- what is curcuminoids
- what is curcuminoid