Vitamin analysis in soft drinks systems

If vitamins are added to a product to make a nutritional claim, it is critical that shelf-life studies are undertaken to prove that the overages added are sufficient to ensure that the label claims can be met at the end of product shelf life. This is important as none of the vitamins are fully stable in a soft drink environment and some, for instance vitamin C, are very quickly lost in the presence of oxygen. The addition of the fat-soluble vitamins to a soft drink also offers a formulation challenge to ensure that they are fully dispersed and that there are no problems with neck ringing during storage. Trace metals, particularly the transition elements, can also have a deleterious effect on vitamin shelf life, and sometimes metal scavengers, such as EDTA or phosphate salts, are added to improve the shelf life. 

Vitamins are generally assayed in one of two different ways. The first route uses a microbiological technique. Here, a specialist organism is used, the growth of which is dependent on the concentration of the particular vitamin of interest. 

These methods are highly sensitive to interferences that limit the growth of the micro-organism and often take rather a long time to perform, as they rely on the growth of micro-organisms under stressed conditions, for example, limited levels of a critical vitamin. However, they do generally offer quite specific methods. Very special skills are required to run these tests effectively. 

The second major, and growing, route is the use of HPLC and either UV or fluorescence detection. Here vitamins are extracted from the product and then assayed using HPLC. This is another very specialised area and is often best left to an expert laboratory, as there may be problems with interferences and losses due to such factors as oxidation during extraction. 

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