Cherry flavour research

In 2013, the German Stiftung Warentest foundation found harmful benzene (a carcinogen) in drinks with cherry flavour; it is theorised that the benzene got into the drinks via benzaldehyde, an essential component of cherry flavouring. A study by the Leibniz-Institute for Food Systems Biology and the Technical University of Munich (TUM) has further analysed the presence of benzene in cherry-flavoured drinks.

When examining soft drinks in 2013, Stiftung Warentest came across small quantities of benzene, with one drink containing just under 4.6 micrograms of benzene per litre. For comparison, in Germany, one litre of drinking water is allowed to contain only one microgram of benzene. At the time, experts at Stiftung Warentest hypothesised that benzaldehyde was the cause of the benzene contaminants observed.

“As our research is specialised on odorants, we followed up on this supposition in the interest of consumer protection and at the suggestion of the German Association of the Flavour Industry,” said Stephanie Frank, lead author from the Leibniz-Institute for Food Systems Biology at the Technical University of Munich.

To do this, scientists first established a reliable, highly sensitive quantitation method of benzene. Then, they carried out experiments with various model solutions which contained benzene-free benzaldehyde. Researchers also examined cherry juice produced under laboratory conditions, to which they also added the pure odorant.

The starting point for the investigations was a pure cherry juice made from sour cherries in the laboratory. Image credit: Gisela Olias/Leibniz-LSB

“Our findings confirm the assumption of the Stiftung Warentest and also explain how the formation of benzene occurs — an important requirement in solving the problem in the long term,” Frank said.

The study revealed that the longer the odorant is exposed to light, the more benzaldehyde is converted into benzene. But the light intensity is also decisive. In contrast, the pH value, the oxygen content, the presence of metal ions or the temperature did not affect the benzene production in the model solutions. No benzene was formed in the cherry juice produced under laboratory conditions during light exposure, with researchers reasoning that it is possible that the dark red colour of the drink acts as a light protection filter, preventing the formation of benzene. The benzene found in soft drinks is probably the result of added cherry flavouring which has already been contaminated with benzene.

“This is why we must be sure to protect flavourings containing benzaldehyde from light, from when the substance is produced to when the product is sold, for example, by storing them in amber glass vials,” said Peter Schieberle, Professor for Food Chemistry at the Technical University of Munich.

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