A comparison of different compounds in blueberries called anthocyanins, responsible for the berry's colour, showed that each anthocyanin had different degradation rates and identified cyanidin glucoside as the most stable natural colorant.

“This study can be used in the field of natural colourants to determine the most stable blueberry anthocyanin in order to achieve the best food colour stability,” wrote the researchers from Slovenia’s National Institute of Chemistry.

“It can also be a very useful tool to determine the shelf life of a product.”

Market value

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.

This is reflected in the market. According to Leatherhead Food International (LFI), the value of the international colourings market was estimated at around $1.15bn in 2007 (€731m), up 2.5 per cent from $1.07bn (680m) in 2004.

Natural colours now make up 31 per cent of the colourings market, compared with 40 per cent for synthetics, according to LFI.

Study details

The Slovenian researchers tested the stability of the anthocyanins in a blueberry-aronia nectar packaged in both carton and glass containers.

“The effect of oxygen [on degradation] has been previously studied but not in commercially-filled products,” explained the researchers. “Other studies have reported on the degradation rates of total anthocyanins during storage and the destruction of anthocyanins during concentrate processing. None of them reports degradation rates of individual anthocyanins during storage.”

Blueberry-aronia nectar was prepared using concentrates of blueberry (Vaccinium angustifolium) and aronia (Aronia melanocarpa), and mixed with water, citric acid, and sugar. The nectars were then packaged in carton or glass containers and stored for 183 days.

A significantly higher degradation rate (22 per cent) was observed in the carton-packaged nectar than in glass, said the researchers.

“This study shows a comparison between nectar packaged in glass and in carton, which is a key study for shelf life evaluation in the fruit packaging industry and for consumer awareness of the impact of different packaging on food quality,” they added.

When the stability of the individual anthocyanins was analysed, cyanindin glucoside was the most stable, followed by peonidin, petunidin, malvidin, and delphinidin.

“As cyanidin glucoside shows the smallest degradation rate, it is the most suitable for food colourant use among the anthocyanins naturally present in blueberry-aronia nectar,” said the researchers.

“High degradation rates of malvidin arabinoside and delphinidin arabinoside suggest that they may be highly susceptible to destruction and less suitable for food colourant use among those tested,” they concluded.

Source: Journal of Food Science
Published online ahead of print, Online Early, doi: 10.1111/j.1750-3841.2008.00909.x
“Anthocyanin Degradation of Blueberry–Aronia Nectar in Glass Compared with Carton during Storage”
Authors: K. Trost, A. Golc-Wondra, M. Prosek, L.Milivojevic