Degradation of folic acid in fortified vitamin juices during long term storage.

Folic acid (FA) concentrations of nine fortified vitamin juices were determined with the aim to study the FA degradation and to investigate the deviation from the declared label value. The juices were received shortly after bottling and were analyzed monthly during controlled storage conditions (light and dark) over one year. The analyses were performed by HPLC-MS/MS, which included a fast "dilute and shoot" sample preparation. Average decreases in FA concentration of 46% were observed after one year. Fresh juices (shortly after bottling) showed the highest deviations from the declared label value (up to+89%). Label values did not reflect the actual concentration of FA in these products, making it difficult to determine the intake of this vitamin.