12 January - 20 June 2016

Scientists explore how orange juice changes colour

25 March 2015

For many consumers the appearance of a food product will highly influence purchasing decisions.  Food items with positive superficial characteristics are perceived to be high quality, a theory as to why orange juice remains one of the most popular beverages worldwide.  Its attractive and vivid colouration, attributed to the composition and concentration of carotenoids, identifies it as being a “highly nutritious product”.

As colour is a key indicator in establishing quality, importance has been placed on understanding the mechanisms which result in colour degradation.  Recent research published in the Journal of Food Chemistry by workers from Belgium claim the first study to explore the changes of carotenoids during storage at both ambient and elevated temperatures, using pasteurised orange juice as an example.  Samples of pasteurised orange juice were stored at 20°C and 28°C for 32 weeks, 35°C for 12 weeks and 42°C for 8 weeks in darkened incubators.   Using existing technologies the samples were tested on a weekly basis for colour measurement and carotenoid analysis.

Browning was clearly detected and became more evident at the more elevated storage temperatures and at prolonged storage.  Results indicated that during storage there was minimal overall decrease in the presence of total carotenoids, suggesting that oxidation reactions are less important than isomerization in the mechanisms of colour change.  It was additionally discovered that individual carotenoids behave differently during storage. ζ-carotene displayed an increase in concentration under storage whereas in comparison other carotenoids decreased as temperature and time increased.  It was found that these changes in carotenoids, correlated to changes found in orange juice colour.  It is believed that the intensification of redness in the orange juice may be accredited to the decrease in certain carotenoids, in particular α-carotene and β-carotene.

While there is initial evidence to support carotenoid changes during storage conditions as a factor for colour change, it can also be hypothesised that non-enzymic browning reactions may play an equally important role due to the appreciable concentration of ascorbic acid in orange juice.  It is concluded that further research is required to understand the complex mechanisms of colour degradation as a whole, looking at the mechanisms for colour instability and not only the influence of carotenoids.

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