The cheese as a habitat

Researchers are deciphering the microbial life on the bark

Countless microbes live on the cheese rind © Elisa Schornsteiner / Vetmeduni Vienna
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The cheese is alive - or at least its bark. Because on her countless microbes cavort. Only their activity produces during maturation the typical aroma of the cheese. What lives on the bark of a mountain cheese, Austrian researchers have now investigated. They found a salt-loving germ originally found in the sea, but also numerous fungi whose exact function is still unknown.

The cheese rind is the interface between cheese and the environment. It protects the inside of the cheese from drying out, but also plays an important role in maturing. Because on the bark lives a variety of microorganisms that take on very different tasks. They decompose proteins and fats on the bark and thus influence the maturation. Some varieties, such as Limburger, Tilsiter and Appenzeller, owe their aroma to bacteria on their bark, while others develop it with the help of molds, such as Camenbert and Brie.

Important also for the health

However, microorganisms on cheese not only make the end product aromatic, durable and easy to eat, they are also of great importance for food safety. Many bacteria on the cheese rind can protect against dangerous germs by forming inhibitors against pathogenic bacteria such as Listeria. They act as a sort of "protective power" for the cheese.

"Understanding exactly which microorganisms are on the bark and what their tasks are in the complex interaction is our research topic, " explains study leader Stephan Schmitz-Esser from the Veterinary University of Vienna. "That way we can help the dairies to produce a safe and tasty cheese".

Cheese bark samples are scraped off for analysis. © Elisa Schornsteiner / Vetmeduni Vienna

Cheese collection for science

While research into the microbial world on cheese has already progressed far and wide in the cheese country of France, this still lags behind German cheeses. The researchers have therefore taken a closer look at the microbial inhabitants of Vorarlberg mountain cheese. This mountain cheese is an origin-protected regional specialty and is produced in large quantities every year. Similar mountain cheeses are also available in the Tyrol and the Allgäu. display

Schmitz-Esser and his colleagues examined cheese samples from three different Vorarlberg cheese shops for their study. In each cellar, they collected 25 to 30 bark samples of cheese of different ages, from very young to old. Subsequently, the scientists subjected the cornea to a detailed genetic analysis to identify the bacterial and yeast strains living on it.

A marine germ and mushrooms

The genetic analyzes have come up with some surprising results. Thus, the most frequently identified gene signature belonged to an old acquaintance but not from the K serei, but from the sea: The bacterium Halomonas is a salt-loving germ, which originally originated probably from the ocean, Because the bark is wetted with salt water before and partly during maturation, the germ feels pretty well here. What function Halomonas germs have exactly on the kesse, but is still unknown.

The analyzes also showed that the composition of the microbes changed during ripening: on the young cows especially Halomonas species romped, as well as the species Brevibacterium aurantiacum. In older mature kisses, on the other hand, the number of Halomonas germs decreases, as the researchers report. The reason: As the bark ripens, so does the salt content. He then took a staphylococcal species.

In addition to a total of 39 species of bacteria, seven types of fungi were found on the bark. Most common was the mold fungus Scopulariopsis brevicaulis. The exact function of these mushrooms also needs to be clarified. Nevertheless, these results provide first insights into what's on the bark's bark and to whom we owe it the typical aroma of this mountain cheese. (Journal of Food Microbiology, 2014; doi: 10.1016 / j.ijfoodmicro.2014.04.010)

(Veterinary Medical University Vienna, May 9, 2014 - NPO)