The herb St. John's wort is commonly used as a herbal remedy, mainly to treat mental disorders and nerve pain, but also as a sedative and antimalarial agent.

Although St. John's wort contains many compounds with biological activity, the major components are hypericin, pseudohypericin and their precursors protohypericin and protopseudohypericin, hyperforin and adhyperforin, flavonol glycosides and biflavones.

There has been increasing interest in the incorporation into foods and beverages of ingredients that provide health benefits. However, there is relatively little information about the stability and safety of these ingredients in the resultant functional foods and beverages. Of the few results available, some fruit drink products labelled as containing St. John's wort have been found to retain components of St. John's wort at an extremely low or non-existent level, highlighting the potential instability of the bioactive compounds.

A study by Ang et al.¹, investigated the effects of pH and light exposure on the stability of pseudohypericin, hypericin, hyperforin and adhyperforin from St. John's wort in aqueous buffer solutions and non-alcoholic, non-carbonated fruit-flavoured drinks. The chemical changes in hyperforin during storage were also studied. These St. John's wort constituents were all found to be unstable in aqueous solutions, especially under light exposure, with the extent of change being different for each compound. Degradation was less severe in the drinks than in the buffer solutions at pH 2.65.
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¹ Ang, CYW; Hu L; Hienze, TM; Cui, Y; Freeman, JP; Kozak, K; Luo W (2004). Instability of St. John's wort (Hypericum perforatum L.) and degradation of hyperforin in aqueous solutions and functional beverage. Journal of Agricultural and Food Chemistry 52 (20) 6156-6164.

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