Confronted by growing consumer demand for natural and healthy foodstuffs, food makers have increasingly been looking for alternatives to artificial food colours such as Sunset Yellow, Tartrazine and Quinoline Yellow.
A growing area of interest has been the use of betalains, water-soluble nitrogen-containing pigments that, depending on their structure, give a red-violet colour (betacyanins) or a yellow-orange colour (betaxanthins).
"Betalains, because of their relative scarceness in nature, have not been much explored as bioactive compounds, but some studies have indicated their potential as antioxidant pigments," wrote Henriette Azeredo in the International Journal of Food Science and Technology .
"These findings have helped to motivate utilisation of betalains as food colourants."
Market figures confirm the trend.
While the European colouring market faces an annual growth rate of about one 1 per cent, the colouring foodstuffs market is ripping ahead on growth of 10 per cent to 15 per cent.
Red-violet colours Azeredo, from Embrapa Agroindustria Tropical in Brazil, presents a timely review of the potential for betalains, and highlights the health benefits of the antioxidant pigments.
The main betacyanin compound found in red beetroots is betanin.
It is listed in Europe as E162, is used in a variety of processed foods.
However, although colours from red beet are currently reported to be about ten times cheaper than colours from other sources, such as papaya and cactus pear, the red beet had several disadvantages, including unfavourable flavour components, no nitrate accumulation, and the risk of microbe carry-over from the earth.
According to Azeredo, the most widely used natural pigments in the red-purple colour range are anthocyanins.
"However, the instability of anthocyanins at pH values above 3 makes betacyanins the natural pigments of choice to provide red-purple colour shades to low acid foods," she stated.
"Moreover, betalains can effectively be stabilised by ascorbic acid, which on the other hand, impairs anthocyanin stability.
Hence, application of betalains instead of anthocyanins for colouring foods with high ascorbic acid contents may be interesting," she added.
Orange-yellow pigments The most widely used natural pigments in the yellow-orange colour range are carotenoids.
However, such compound are poorly soluble in water, which limits the applications that such pigments can be used in.
"Although betaxanthin sources are much scarcer worldwide, their water solubility could propel their application as yellow-orange food colourants in situations when the water solubility is crucial," wrote Azeredo.
And one source coming in for increased attention is the cactus pear, whose pigments do not possess unfavourable flavour components.
"The commercial exploitation of cactus fruits as alternative sources of food colourants may not only provide a wider colour spectrum than the red beet without its negative sensory impacts, but also contribute to the sustainable development of the usually underdeveloped semi-arid regions which could supply markets with cactus fruits," she wrote.
Further research Questions still remain and avenues remain under-explored, said Azeredo.
First of all, it may be possible to generate crops with improved characteristics, "such as beets with increased betalain levels and less or no earth-like flavour," she said.
Producing the pigments using cell cultures may also be improved, she said, which would reduce costs associated with the pigments.
Finally, Azeredo recommended further investigation of the health-promoting properties of the pigments.
Source: International Journal of Food Science and Technology Published online ahead of print, doi: 10.1111/j.1365-2621.2007.01668.x "Betalains: properties, sources, applications, and stability - a review" Author: H.M.C.Azeredo