Root vegies the new source of natural colourings

Heirloom vegetables such as purple sweet potatoes and black or purple carrots may have been embraced by the foodie movement in recent years, but they’ve also been adopted by another group: the food industry. These vegetables have become sources of a new generation of natural food colourings replacing traditional synthetic colours, as well as beetle-derived colours.

Speakers at the 246th National Meeting & Exposition of the American Chemical Society (ACS) described how natural colours that were in use centuries ago are making a resurgence in response to consumer preferences, manufacturers’ needs and the potential health benefits of these antioxidant-rich substances.

“The natural colours industry for foods and beverages is gaining in value as US and international companies move towards sustainable and affordable crop alternatives to synthetic red colours and red colours derived from insects,” explained Stephen T Talcott, PhD, from Texas A&M University, who spoke at the event.

Root crops like black carrots and purple sweet potatoes (PSPs) are grown specifically for the natural colours industry, Talcott said. They have become primary agricultural products, compared to fruits such as grapes, which are grown for other purposes and used as secondary or byproduct-based colours.

A range of colours from light pink to rose, red and deep purple can be obtained through the use of pigments in PSPs. Baked, used for French fries or prepared in other ways, PSPs taste like regular sweet potatoes, Talcott noted. PSPs have the same anthocyanin pigments found in black cherries.

PSP anthocyanins have proven to be among the best for food and beverage colouring, he said, citing fruit drinks, vitamin waters, ice cream and yoghurt. They are stable, do not break down easily, have superior colouring properties and a relatively neutral taste (in contrast to the slightly earthy, bitter taste from grape-based colourings). The pigments, however, are very difficult to extract.

PSP anthocyanins have advantages over traditional synthetic red food colourings and the ‘carmine’ reds extracted from cochineal insects. Those include sustainability and ease of production. Cochineal insects feed on a type of cactus native to South America and Mexico. It takes about 2500 bugs to produce one ounce of cochineal extract.

However, PSP anthocyanins are difficult to extract. Talcott reported on development of a new process that extracts larger amounts of pigment from PSPs. Byproducts of the process include starch and fibre, which could be used as animal feed, in various food applications or as a raw material for biofuel production. Alternatively, the byproducts could simply be composted and used as a soil conditioner for producing more PSPs or other crops.

Such processes could encourage development of a domestic natural food colouring industry, with agriculture spreads devoted specifically to growing foods for use in making food and beverage colouring. Currently, the United States imports much of the natural food colouring it uses commercially. The small amounts of PSPs grown domestically go mainly to sales of fresh potatoes for the table.

The 246th National Meeting & Exposition of the ACS features almost 7000 reports on new discoveries in science and other topics.