Stability of St John's Wort components in flavoured drinks

There is a growing market for food and drinks with health benefits, and a number of popular botanicals including St John's Wort have been used as ingredients in conventional foods or sold as "functional foods".

A team of American and Chinese researchers have made a detailed study of the fate of biologically active compounds in St John's Wort at various acidity levels and under dark and light conditions.Their results indicate just how unstable may of these active principles are.

St John's Wort

St John's Wort is a widely used herbal antidepressant, which is treated as a drug in Germany but as a dietary supplement in the United States.

It contains many compounds with documented biological activities, the main classes being naphthodianthrones (hypericin and psesudohypericin and their precursors, protohypericin and protopseudohypericin respectively), phloroglucinols (hyperforin and adhyperforin), flavonol glycosides and biflavones.

A review of the literature by Ang and her colleagues indicates that a number of studies have already shown that St John's Wort products are unstable and that there is uncertainty as to whether it is hypericin or hyperforin which is responsible for the its antidepressant effects.

The objectives of Ang's study were to determine the effects of pH and light exposure on the stability of selected, unique active components of St John's Wort, namely pseudohypericin, hypericin, hyperforin and adhyperforin in aqueous buffer solutions and non-alcoholic, non-carbonated, fruit-flavoured beverages.

Results indicated that St John's Wort components were unstable in acidic aqueous solutions. More changes were observed during light exposure, with hyperforin and adhyperforin decreasing the most. Less dramatic changes were seen in the fruit flavoured beverage samples than in the buffer solution at pH 2.65.

The authors speculate that this may due to the protective effects of other ingredients in the beverage. The major degradation products of hyperforin in acidic aqueous solution were furohyperforin, furohyperforin hydroperoxide and furohyperforin isomer a. This last compound was also found in the drink product containing St John's Wort as an ingredient.

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Reference
Ang CY, Hu L, Heinze TM, Cui Y, Freeman JP, Kozak K, Luo W, Liu FF, Mattia A, DiNovi M. (2004). Instability of St. John's wort (Hypericum perforatum L.) and degradation of hyperforin in aqueous solutions and functional beverage. J Agric Food Chem, 52, 6156-6164