FOOD CHEMISTRY: FOOD COLOURS
Diagram
Colour from nature, colour from the factory
Natural food colour
From plants, animals or minerals. Annatto, anthocyanins, carotenoids, curcumin and chlorophyll are examples.
↓
Synthetic food colour
Made in a factory by chemical synthesis. Tartrazine, Sunset Yellow and Allura Red are examples.
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The key point
Both colour food, but they differ in source, stability, strength and cost.
Figure 1: Natural colours come from plants, animals or minerals; synthetic colours are made by synthesis. Drawn in our own style from Scotter, Colour Additives for Foods and Beverages, which reviews the natural and synthetic colours available, and the pigments chapter of Velisek, Koplik and Cejpek, The Chemistry of Food. Note: this pair was flagged as chapter level and not yet verified in a dedicated search, and it was re-checked at build time through the Google Books page for Scotter, which reviews natural and synthetic colours together.
Introduction
Natural and synthetic food colours both colour food, but they come from different places and behave differently. A natural colour comes from a plant, animal or mineral source, such as annatto from seeds, anthocyanins from berries, carotenoids from carrots, or curcumin from turmeric. A synthetic colour is made in a factory by chemical synthesis, such as tartrazine, Sunset Yellow or Allura Red. The source decides the stability, the strength, the cost, and how the colour is labelled.
Scotter reviews the natural and synthetic colours available, their properties and applications, and Velisek, Koplik and Cejpek cover pigments and other colourants. This article follows those two books.
Quick comparison
Table 1: Natural food colours compared with synthetic food colours
| Aspect | Natural food colours | Synthetic food colours |
|---|---|---|
| Source | Plants, animals or minerals | Chemical synthesis in a factory |
| Examples | Annatto, anthocyanins, carotenoids, curcumin, chlorophyll, beet betalains | Tartrazine, Sunset Yellow, Allura Red, Ponceau 4R, Quinoline Yellow |
| Colour strength | Often weaker, so more is needed | Strong, so a small amount colours a large batch |
| Stability to light | Often fades in light | Often more stable in light |
| Stability to heat | Often fades or changes on heating | Often more stable to heat |
| Stability to pH | Often changes colour with pH, as anthocyanins do | Often stable across a wide pH range |
| Cost | Often more costly, and supply depends on crop and season | Often cheaper and available all year |
| Purity and consistency | Varies with crop, season and extraction | High chemical purity and batch to batch consistency |
| Labelling | Labelled as natural colour, or by source name | Labelled by colour name or number, under food additive law |
| Consumer view | Often preferred by shoppers who want natural food | Often viewed with suspicion, even where the law permits them |
Scientific explanation
Definition
A natural food colour is a colouring substance taken from a plant, animal or mineral source, such as annatto, anthocyanins, carotenoids, curcumin or chlorophyll. A synthetic food colour is a colouring substance made by chemical synthesis, such as tartrazine, Sunset Yellow or Allura Red. Scotter reviews both groups together, with their properties, applications, and regulatory and safety issues, and that review is the source for this article.
Working principle
A natural colour is an extract: the pigment is taken out of its source with other compounds from the same material, and its colour comes from the pigment molecule itself. Because it is a natural molecule, it is often sensitive to light, heat and pH, so the colour fades or changes in processing and storage. A synthetic colour is a single chemical made to a set purity, so its colour is strong and stable, and the same shade can be made batch after batch. The difference is therefore in stability and consistency as much as in source.
Apparatus
The books used here name no laboratory apparatus for telling the two apart, so no apparatus list is given.
Measurement procedure
The books used here name no single standard laboratory procedure for telling a natural colour from a synthetic one by eye. Scotter covers methods of analysis for colour additives, including spectrophotometry and chromatography, but the distinction is made from the source and the additive declaration, not from one simple test. The books give no worked food example with numbers for this comparison, so none is given.
Factors affecting readings
Light, heat, oxygen and pH change natural colours faster than synthetic ones. The food itself, its acidity and its storage time, change how long a natural colour lasts. The law decides which colours may be used and how they must be declared, and Scotter covers those regulatory issues.
Formulas and calculations
The books used here give no formula for this comparison, so no formula or worked calculation is given.
Industrial applications
- Natural colours are used in drinks, sweets and dairy foods where a natural label is wanted.
- Synthetic colours are used in sweets, soft drinks and snacks where a bright, stable colour is wanted.
- Annatto is used to colour cheese and butter a yellow colour.
- Curcumin is used to colour curries, drinks and confectionery yellow.
- Synthetic colours are used where the same bright shade must be made batch after batch.
Advantages and limitations
- Natural colours: advantage: meet consumer demand for natural food and come from familiar sources. Limitation: weaker, less stable to light, heat and pH, and more costly.
- Synthetic colours: advantage: strong, stable, consistent and cheap. Limitation: cannot be labelled natural, and some shoppers reject them.
- Natural colours: advantage: often carry other compounds from the source. Limitation: supply and shade vary with crop and season.
FAQ
Is a natural colour always safer?
No. Both groups are controlled by food additive law, and Scotter covers the safety analysis of both. Natural does not mean unregulated.
Why do natural colours fade?
Natural pigment molecules are sensitive to light, heat and pH, so the colour changes in processing and storage.
What is tartrazine?
Tartrazine is a synthetic yellow food colour, made by synthesis, and it is one of the colours Scotter lists.
Why do makers still use synthetic colours?
They are strong, stable, consistent from batch to batch, and cheap, so the same shade can be made all year.
References and further reading
- Michael J. Scotter, Colour Additives for Foods and Beverages, Elsevier, 2015 (Google Books page read)
- J. Velisek, R. Koplik and K. Cejpek, The Chemistry of Food, Wiley, 2020, chapter on pigments and other colourants (Google Books page read).
- Mathew Attokaran, Natural Food Flavors and Colorants, Wiley, 2011 (Google Books page read).
