[Food science] What are the causes of product colour fading?

What are the causes of product colour fading?

This is one of the most frequent problems, and sources of the complaint, that beverage manufacturers encounter. It is a problem that may have several possible causes the most likely of which is exposure of the product to excessive amounts of light. It is also noteworthy that fading is normally associated with the use of added colours, either natural or artificial, rather than the intrinsic colour of a pure fruit juice.

Products should be shelf tested in both south-facing and north-facing light to represent both direct sunlight exposure and the more normal daylight to assess their overall susceptibility to light. For products that are light-sensitive, use of protective films can be of value as can wrap-round labels. Another approach is to shrink wrap bulk packs in the protective film.

Other likely causes are the presence of ingredients such as sulphur dioxide and ascorbic acid and the initial (or subsequent) level of oxygen in the product as colour fading appears to be linked to oxidative processes.

Almost all colour fading problems are best solved by an empirical approach to determine the optimum level of ascorbic acid which will probably be around 100 mg/L. Strenuous efforts should be made to ensure minimal oxygen levels at bottling and the avoidance of containers that allow oxygen ingress. 

• BetaCarotene is completely bleached by oxygen but can be protected by the presence of ascorbic acid. 
• Sunset Yellow colouring (E110) fades from red/orange to pale yellow in the presence of sulphur dioxide.
• Carmoisine (E122) is completely bleached by ascorbic acid