The red seeds from the fruit of the annatto tree have been used for centuries to color food, hair and skin. The seeds contain the red fat-soluble colorant bixin and the water-soluble version norbixin, both of which belong to the pigment group of carotenoids.

Today, the natural colorants are used primarily to add color to a wide range of foods, such as dairy products like cheddar cheese. However, it is associated with challenges for the food technology:

- Both consumers and industry have a strong wish to replace artificial colorants with a natural alternative, and the use of the colorful seeds from the annatto tree is a good solution. Norbixin is also one of the most widely used natural colorants in the food industry thanks to its water-soluble properties, which make it more suitable in several types of food than bixin. However, the color is more likely to fade when compared to artificial colorants. In order to be able to do something about it, we need to understand the mechanisms behind the fading, says Anders Hauer Møller, postdoc at the Department of Food Science.

In collaboration with the ingredient company Chr. Hansen, researchers from the research group Food Chemistry and Technology at the Department of Food Science have focused on the problem - and the efforts have provided exciting results.

Chain mechanisms may be involved

Using highly sensitive mass spectrometry equipment, researchers now have a better idea of ​​how norbixin behaves:

- We have identified a number of chemical compounds that have been created during storage of norbixin in aqueous solutions. These compounds can be divided into two groups: compounds with lower mass than norbixin and compounds with higher mass than norbixin - that is, degradation products and oxidation products, and it is the latter that are really interesting in this context, says Anders Hauer Møller, and elaborates:

- In previous studies of carotenoids, the research has often only found single oxidation products, but in our study, we have been able to detect norbixin with many oxidations. We therefore hypothesize that the oxidation of norbixin involves a chain reaction mechanism, where the oxidation is initiated on one norbixin, which then reacts further with a new norbixin, or perhaps the same norbixin, and so on. This is completely new knowledge.

The researchers examined samples stored in light and in the dark:

- To our surprise, we do not see any major differences in the oxidation products found in the different samples. However, we can see that light accelerates the process in which oxidation products are formed. We have also investigated whether reactive oxygen species initiate the chain reaction, but it does not seem to be the case, says Anders Hauer Møller.

Vitamin E can slow the oxidation

The researchers already have an idea of ​​how to stop the chain reactions that take place during oxidation:

- Once the chain reaction is started, something needs to be done to stop it. From previous studies, we know that Vitamin E is an effective chain-breaking antioxidant. Therefore, it might give a good effect to add Vitamin E in foods with norbixin, says Anders Hauer Møller.