Foods sold on the European market are regulated, but much less strictly than medicines, which is why the authenticity of the products composition is not regularly controlled. We investigated the actual content of hydrophilic vitamins (vitamin C and B complex) in foods and food supplements. We determined whether the tested products contain the vitamins stated, in which concentrations and how obtained results correlate with the label claims.
For this purpose, we used a previously developed UHPLC method with DAD detection. The method was initially validated according to the ICH guideline to confirm its suitability for the proposed use. Hereinafter, we developed and optimized sample preparation procedure for vitamins extraction from food and food supplements in various forms. We analysed different groups of samples: waters with added vitamins, energy drinks, effervescent tablets, juices, powdered drink mixes, and candies. The sample preparation procedure was adjusted to the composition and complexity of each sample.
The developed analytical procedure was used to evaluate the quality of 36 different commercial products containing hydrophilic vitamins. We determined the actual vitamins contents and compared it with the contents indicated on the packaging. Vitamins B7 and B12 are added to the products in very low (μg) amounts, so their concentrations were often not quantitatively determined. Due to less strict regulations for foods, significant variations between the declared and the contents of determined vitamins were observed. In general, vitamin contents were higher than declared. This is mostly associated with instability of vitamins during production and storage. Therefore, manufacturers usually add overages in order to ensure proper vitamin contents at the expiration life. The found vitamins overages were mostly 15-35%. On the other hand, some vitamins were determined in lower amounts than stated, e.g. vitamin C in the majority of the tested products (78%) or were labelled but not detected (vitamin B6 in two products). In general, fewer deviations from the label claims were observed among liquid than solid products. Content tolerance limits were more frequently exceeded in foods. Except for some food supplements, manufacturers rarely specified the added vitamin form.
The obtained results of the analysis are useful for consumers, who cannot check the composition and quality of products themselves, and are a good basis for further research.
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