Replacing artificial food dyes is not as simple as swapping in a colorful plant extract. Natural pigments can fade during processing, change shade depending on acidity and break down before a product reaches the end of its shelf life.
New research suggests pigments derived from purple corn may overcome some of those challenges. In laboratory tests, the colorants retained much of their color after heating and remained relatively stable for several weeks in a model beverage.
The findings do not mean purple corn is ready to replace every synthetic dye used in food. Researchers tested concentrated extracts and experimental formulations, not finished products sold to consumers. The study, led by scientists at the University of Missouri and published in npj Science of Food, also did not show that using the pigments would make a food healthier.
Purple corn gets its red, purple and blue shades from anthocyanins, the same broad group of plant pigments found in blueberries, grapes and red cabbage. In corn, they are concentrated in the pericarp, the thin outer layer of the kernel.
“It’s the layer that often gets stuck in your teeth,” said Pavel Somavat, a University of Missouri researcher with appointments in agriculture and engineering. “In purple corn, that’s where our most valuable components are.”
Food manufacturers are increasingly interested in plant-based colorants as regulators and consumers scrutinize synthetic dyes such as Red No. 3 and Red No. 40.
But performance remains a major obstacle. A colorant must survive manufacturing, transportation and storage while maintaining a predictable appearance.
“Most natural colors are fragile,” Somavat said. “They tend to break down when exposed to heat, light or oxygen.”
The researchers extracted anthocyanin-based colorants from purple corn and tested how they responded to heat, storage and different levels of acidity. They also compared uncoated extracts with powders made using protective food-grade materials.
After one hour at temperatures used in some food-processing applications, approximately 75% of one key pigment remained intact.
Encapsulation improved retention for some compounds, with certain protected formulations preserving nearly 97% under the tested conditions.
Those results do not mean every pigment or formulation performed equally well. Stability varied depending on the compound, processing method, temperature and storage conditions.
The team also tested the colorants in a model beverage system. That is an experimental liquid designed to mimic some of the conditions found in commercial drinks, not an actual fruit juice, sports drink or flavored water sold to consumers.
The pigments were generally more stable under refrigeration than at warmer temperatures. Acidic conditions also helped preserve many of the anthocyanins, while changes in pH shifted the color from red toward purple or blue.
After seven weeks of refrigerated storage, several formulations retained much of their color. Warmer conditions caused substantially more degradation.
“Purple corn-based colorants held up well in acidic and basic environments,” Somavat said. “That makes it a strong candidate for fruit juices, flavored waters and sports drinks.”
The researchers also used a laboratory model of digestion to examine how the pigments changed under conditions intended to resemble the gastrointestinal tract.
That type of experiment can show how compounds may break down during digestion. It cannot determine how much a person would absorb, whether the pigments would reach specific tissues or whether they would produce a health benefit.
The news release describes anthocyanins as antioxidants associated with lower inflammation and better heart health. This study did not test those outcomes.
It did not include people or animals, and it did not measure inflammation, cardiovascular health or any other clinical result.
A laboratory antioxidant test also does not establish that eating the ingredient will produce the same effect in the body.
That distinction matters because replacing a synthetic dye with a plant pigment does not automatically improve a product’s overall nutritional profile. A sugary drink or candy remains high in sugar even when its color comes from purple corn.
The ingredient may still be valuable for manufacturers seeking a plant-derived color with better stability. But color source, nutritional quality and health effects are separate questions.
The researchers are also working to adapt purple corn varieties for Midwest growing conditions. Some deeply colored South American varieties do not perform well in the Corn Belt, so the team is crossing them with corn already suited to Missouri and surrounding states.
“Some of the most colorful types don’t grow well here, so we’re crossbreeding them with types of corn that already do well in places like Missouri,” said Sherry Flint-Garcia, a research geneticist with the U.S. Department of Agriculture’s Agricultural Research Service.
That work could eventually create another specialty crop for farmers while giving food companies a domestic source of natural colorants.
Commercial use would still require additional testing. Researchers would need to determine how the pigments perform in different foods, whether consumers accept the resulting colors and flavors and whether the ingredient can be manufactured consistently at scale.
Regulatory and safety questions would also need to be addressed before a concentrated purple corn extract could be widely used as a color additive.
The research was supported by the USDA National Institute of Food and Agriculture.