Produce-aisle pigments could replace synthetic dyes and insect-based food coloring. However, the extraction of the colorants from crops poses a challenge to chemists.

Purple sweet potatoes hold particular promise as pigments. Purple sweet potatoes contain anthocyanins, the same chemical that clothes concord grapes in purple and gives raspberries a ruby hue.

As a food coloring, anthrcyanins could be used to create colors ranging from delicate pink to rose red to imperial purple. However, techniques for collecting the dyes from the plants tend to be expensive and inefficient compared to the production of other colorants. Chemists from Texas A&M; University recently reported on advances they made in producing red dye from purple spuds.

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“The natural colors industry for foods and beverages is gaining in value as the United States and international companies move towards sustainable and affordable crop alternatives to synthetic red colors and red colors derived from insects,” said Stephen T. Talcott of Texas A&M; in a press release. “In addition to adding eye appeal to foods and beverages, natural colorings add natural plant-based antioxidant compounds that may have a beneficial effect on health.”

Talcott presented his teams’ advances at the American Chemical Society meeting occurring this week in Indiana. The left-overs from Talcott’s process can be fed to livestock, used to produce biofuel or composted.

Currently, most red food coloring originates in a lab, while some comes from the cochineal insect. Approximately 2,500 cochineal insects must be sacrificed to create one ounce of carmine, a red dye used in candy, yoghurt, ice cream and other foods.

Cochineal insects dine on prickly pear cactus in Mexico and Central America. The bugs have been collected for centuries to make dye. The bugs once reddened the robes of Aztec emperors, then became the center of a lucrative international trade, until competition from cheaper synthetic dyes reduced demand.

The purple potato anthocyanins, which could replace both bug and lab-made dyes, may have health benefits, but the jury is still out.

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A 2009 study in the Journal of Medicinal Food suggested that anthocyanins may attach to the same brain sites as marijuana and may have pain-killing and anti-inflammatory properties. Anthocyanins are anti-oxidants, chemicals that can help reduce harmful and carcinogenic substances in the body. However, doctors haven’t found proof that the anthocyanin anti-oxidants survive beyond the digestive system.

IMAGE: Genetic varieties of heirloom potatoes:  Red Erik, Snowball, Cariboo, Purple Peruvian, Caribe, and French Red. (David Cavagnaro/Corbis)