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.
"The so-called colouring foodstuffs representing aqueous or oily plant extracts extend their market share with red-coloured preparations being particularly requested," wrote lead author Patricia Esquivel from Hohenheim University.
"In this regard, pitaya fruits from the genotype Hylocereus have been proposed as promising colour sources."
Market figures confirm the trend.
While the European colouring market faces an annual growth rate of just 1 per cent between 2001 and 2008, the colouring foodstuffs market is ripping ahead on growth of 10 per cent to 15 per cent.
Betanin, the main betacyanin compound found in red beetroots and listed in Europe as E162, is used in a variety of processed foods because it colours without changing the flavour profile.
In background information in the study, published in the journal Innovative Food Science & Emerging Technologies, the authors state that although colours from red beet were currently ten times cheaper, the red beet had several disadvantages, including unfavourable flavour components, no nitrate accumulation, and the risk of microbe carry-over from the earth.
The scientists looked at pigment profiles, betalain contents, and colour in five Hylocereus sp. genotypes originating from Costa Rica.
While significant differences in colour were observed in fruit pulps from "San Ignacio" and "Nacional", and "Lisa" exhibited the most reddish tint, said the researchers.
The highest betalain contents were found in "San Ignacio" and "Orejona", with "Nacional" having the lowest values.
"Apart from the newly reported betalains neobetanin and gomphrenin I, indicaxanthin was the first betaxanthin so far detected in pitaya fruits," said the researchers.
Esquivel and co-workers called for further studies to investigate if pigment characteristics allow reliable genotype differentiation independent of the date of harvest and seasonal factors.
"To secure the authenticity of the plant material, a reliable differentiation of pitayas from different origins is required," concluded the researchers.
"In addition, Hylocereus fruits may differ in their colour quality and pigment content, the knowledge of which is crucial for the selection of appropriate plants for an emerging pitaya market."
The Hohenheim researchers are also working on betalain-rich extracts from cactus pear.
The main limitation for commercialisation of the cactus pear pigments at this moment appears to be the current market prices of the fruit, but may be economical as a functional ingredient since the concentrate is also rich in amino acids, calcium, magnesium, and moderate levels of vitamins.
Source: Innovative Food Science & Emerging Technologies doi:10.1016/j.ifset.2007.03.022 Pigment pattern and expression of colour in fruits from different Hylocereus sp. genotypes
Authors: Patricia Esquivel, Florian C. Stintzing, and Reinhold Carle