Coumarin is a secondary plant compound that lends its characteristic odour to fresh hay and dried woodruff. It is also contained in various species of the papilionaceae family, in dates, tonka beans and in various types of cinnamon. Along with woodruff, Chinese cinnamon (cassia) – as opposed to Ceylon cinnamon - contains comparatively high concentrations of coumarin.
The initial substance for coumarin synthesis in the plant is cinnamic acid. Coumarin is glycosidically bound in the plant and only released when the cell structure is destroyed and the sugar is split off as a result. The glycoside is hydrolised with the corresponding glycosidase to release coumarin.
What risks does coumarin imply?
In early 2007 coumarin was in all the German headlines after increased coumarin concentrations had been found in baked Christmas goods containing cinnamon. These exceeded the maximum allowance level by far. The substance can damage the liver and showed a carcinogenic effect in animal testing, when these were given higher doses of coumarin. Its use as a flavouring agent was restricted by law both in the US and in the EU because of its hepatotoxic effect. Since 1988 the use of coumarin as a flavouring agent in food has been prohibited by Flavouring Directive 88/388/EC and later by Flavouring Regulation (EC) No. 1334/2008. Statutory maximum values of 5 mg/kg in desserts, 15 mg/kg in fine bakery ware (with the exception of traditional and/or seasonal bakery ware containing a reference to cinnamon in the labelling; in these, the maximum value is 50 mg/kg), and 20 mg/kg in breakfast cereals including muesli have been defined. So far there is no defined maximum value for the coumarin concentration in cinnamon.
Specification of the maximum level was based on the assumption that the carcinogenic effect observed in animal testing was caused by changes in the genetic material. This, however, was refuted by the European Food Safety Authority (EFSA) in 2004, when continued research led to new findings. For the first time a tolerable daily intake (TDI) of 0.1 mg per kg of body weight was defined.
Chinese cinnamon, which contains approx. 3 g of coumarin per kg, has a particularly high concentration of coumarin. Surveys with 2 to 5-year-olds who had consumed coumarin-rich foods such as “Zimtsterne” (traditional German Christmas biscuits containing cinnamon), i. e. containing 70 mg/kg coumarin, led the Federal Institute for Risk Assessment (BfR) to conclude a 3-fold exceedance of the TDI level.
In the cosmetics industry coumarin is frequently used as a fragrance in lotions, shower gels and perfumes. Although it is easily resorbed through the skin, it may still be used without restriction as a fragrance in such cosmetic products. Due to the sensitising potential, however, Regulation 2003/15/EC obliges manufacturers to declare concentrations of more than 0.001 % in leave-on products (e.g. body lotions) and concentrations of more than 0.01 % in rinse-off products (e.g. shampoo).
ifp Institut für Produktqualität offers the analysis of coumarin in foods, along with a wide range of other contaminants. Quantitative determination of the substance is done by high performance liquid chromatography (HPLC).