Seeds of the Osmanthus fragrans plant may offer a novel red colour for food formulators, and tap into the growing demand for natural colours, says new research from China.
Osmanthus fragrans, also known as the sweet or fragrant olive, has a long history of use in Chinese cuisine with the flowers providing fragrance to teas, jams, soups, and dumplings. However, its use in the EU is not known, and therefore any introduction here would require novel foods approval.
“In a broad sense, the good characteristics of [the red pigment] give it potential for use by the food processing industry as an additive. Considering its excellent free radical scavenging capability, it can be also used as an antioxidant,” wrote lead author Yingming Pan from Guangxi Normal University.
According to research published in the journal Food Chemistry, said to be the first of its kind, pigments extracted from the plant’s seeds could offer a natural alternative to synthetic colours.
The main natural red pigments are anthocyanins, betalains, and carotenoids sourced from berries and grapes, red beetroot, and red fruit, vegetables and flowers, respectively, according to Leatherhead Food International (LFI).
The most widely used natural pigments in the red-purple colour range are anthocyanins. However, these compounds are relatively unstable above pH 3. This means that betacyanins, and betalains in particular, are the natural pigments of choice to provide red-purple colour to low acid foods.
The researchers extracted the pigment fro the seeds of O fragrans and report that it showed good solubility in both alkaline and acidic waters. As with other pigments, the colour was affected by the pH of the solution, with a red colour observed at low pH (pH 1-5), changing to a henna colour at pH 7-10. Above pH10 a green colour was observed, said the researchers.
Pan and co-workers report: “No evident influence of sodium chloride as food additives on the pigment stability was observed.” Good heat stability was also reported.
However, they note that the pigment was not resistant to chemical oxidation, and stressed that “oxidizers should be avoided when refining, processing and using of the pigment”.
Using the 2,20-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl radicals methods to evaluate the antioxidant activity of the pigment, they report that the pigment exhibited “excellent” activity, and noted that it was “superior to butylated hydroxytoluene (BHT)”, a commonly used synthetic antioxidant.
The return to ‘natural’
The food industry is experiencing a shift back to the use of natural food colours in foods. Natural colours lost their appeal when synthetic colours arrived on the scene, as they provide less consistency, heat stability and colour range than their chemical alternatives. Moreover, natural colours are more expensive.
However, as consumer awareness increases over the link between diet and health and trends move towards more clean-label products, natural colourings are back in fashion.
One of the most significant studies deterring consumers from artificial colourings was the Southampton Study, published in The Lancet, which found that a concoction of artificial colours led to hyperactivity in children.
Source: Food Chemistry15 February 2009, Issue 4, Volume 112, Pages 909-913“Characterisation and free radical scavenging activities of novel red pigment from Osmanthus fragrans’ seeds”Authors: Y. Pan, Z. Zhu, Z. Huang, H. Wang, Y. Liang, K. Wang, Q. Lei, M. Liang