Identifying a true mountain cheese

Terpene profiles could be used to authenticate cheese

Swiss chemists have filled in some of the holes in understanding the chemistry of Switzerland’s much sought after and economically important mountain cheeses. The mark of a true mountain cheese lies in a characteristic blend of terpene molecules, they report.

Terpenes are bioactive secondary plant metabolites that form the key components of essential oils. But the terpene-like molecules found in dairy products are not necessarily the same as those found in the plants that cattle feed on, says Hedwig Schlichtherle-Cerny, head of the flavour laboratory at Agroscope Liebefeld-Posieux, based at the Swiss Federal Research Station for Animal Production and Dairy Products in Berne.

Schlichtherle-Cerny and colleagues used so-called purge and trap GC-MS to analyse the terpenes found in plants, in milk, and in a much-loved mountain cheese, raclette. They picked several types of plant at different sites in Switzerland at altitudes between 1400 m and 1920 m, they tested milk from farms in those areas, and cheese that was made from that milk.

The predominant terpenes found in the plants included ?-myrcene, and two limonene enantiomers: (+)- and (-)-limonene. The picture was different in milk. ’Surprisingly, we found further monoterpenoids and tentatively identified 3,7-dimethyl-1,6-octadiene; 2,6-dimethyl-2,6-octadiene; 3,7-dimethyl-2-octene and also camphane, which had all been absent in grass,’ Schlichtherle-Cerny told delegates attending the 228th National Meeting of the American Chemical Society. This was ’basically the same’ to the profile seen in raclette cheese, she added.

Many of the molecules found in milk and cheese had only one or possibly two double bonds, while many of the monoterpenes found in the plants had two or three, says Schlichtherle-Cerny. This led her to hypothesise that hydrogenation reactions occurring in the animals’ digestive system could be responsible for the difference.

To test this, her team focused on the rumen, the cow’s first stomach where food is partially digested by bacteria. The rumen microflora is strictly anaerobic and produces hydrogen and other gases enabling the conversion of, for example, unsaturated fatty acids to saturated ones.

Schlichtherle-Cerny’s team took one plant species from those they had sampled - cow parsnip, a terpene-rich relation of cow parsley that frequents Swiss pastures - and studied the effects of rumen microflora on the plant’s monoterpene composition. They mixed ground cow parsnip with phosphate buffer and rumen fluid, removed from healthy living animals, and incubated the mixture at rumen temperature (39?C) for 24 hours.

Following this, the monoterpenes present in cow parsnip were nearly all degraded by at least 50 per cent, including the two limonene enantiomers found earlier in plants. At the same time, new monoterpenoids were formed, including 3,7- dimethyl-1,6-octadiene and 2,6-dimethyl-2,6-octadiene, both of which had been detected in milk and raclette cheese.

The researchers found a significant correlation between degradation and formation - as ?-myrcene levels fell, for example, so 3,7- dimethyl-1,6-octadiene levels rose - concluding that the rumen environment could account for all these reactions.

Understanding terpene composition may allow the discrimination of highland and lowland produce. Terpene profiles could serve as ’terroir’ markers and prove a useful authenticity test for produce with a protected designation of origin - so-called PDO products. Schlichtherle-Cerny now plans to look for similar markers in meat products that will point to where or how a given animal has been farmed.

Bea Perks/Philadelphia, US