Biogenic amines in foods represent a health risk. Researchers from Agroscope and INRAE investigated the formation of these undesirable substances in raclette cheeses by the bacterium Morganella morganii.
When scientists investigate the wide range of bacteria present in cheese, they find, among others, Morganella morganii – a gram-negative bacteria that is commonly found in the environment and in the digestive tracts of mammals. This bacterium is undesirable in fish products, since it forms large amounts of the biogenic amine histamine. When consumed, it can cause symptoms similar to poisoning (e.g. abdominal pain, headache and skin-flushing). Researchers from Agroscope and the French research institute INRAE addressed the question of whether Morganella morganii bacteria,which were isolated from cheeses, can also form histamine in cheeses. In vitro laboratory experiments showed that not only histamine but also putrescine and cadaverine are formed by the cheese isolates. The latter two substances also belong to the biogenic amines, and can exacerbate the effect of histamine consumed at the same time.
Study suggests health risk of Morganella morganii in cheese
In the experiments, scientists made smear-ripened raclette cheeses by inoculating pasteurised milk with Morganella morganii, then processing it into raclette. As a control, they also made raclette cheeses without Morganella morganii. During the 130-day ripening period the researchers took sample material at various times from the rind and curd of the cheeses. Both the Morganella morganii bacterial count and the amount of biogenic amines in them were determined.
The experiment showed that Morganella morganii survived the cheesemaking process and multiplied over the first 24 hours. At the end of the ripening period, researchers could only identify living cells in the rind. Unlike with the control cheeses, putrescine and cadaverine accumulated in the cheeses with Morganella morganii. The cadaverine content was significantly higher in the rind (310 mg/kg) than in the curd of the cheeses (160 mg/kg). The researchers also detected histamine in the cheeses with Morganella morganii, albeit in low concentrations (<50 mg/kg).
Regular use of specific detection methods for Morganella morganii would be appropriate
Although there are no limits stipulated for biogenic amines in cheeses, based on these results Morganella morganii should be viewed as an undesirable bacterium for cheese. To date, there have been no data on the spread of this bacterium in Swiss cheeses. Morganella morganii grows very well on selective agar, which is used for the quantitative detection of enterobacteria. The enterobacteria are hygiene indicator bacteria in many foods. Previously, when determining the count of these bacteria in cheese products, Morganella morganii has presumably often been overlooked. The detection methods developed for the study can be used to detect Morganella morganii specifically and quantitatively in cheeses. For one thing, this will allow both the spread and origin of Morganella morganii in dairy products to be traced and investigated in greater depth in future.
- The Morganella morganii bacterium grows well in the cheese.
- If Morganella morganii is present in cheese it can form biogenic amines, particularly putrescine and cadaverine.
- Further research is needed to determine the sources of contamination and the spread of this bacterium in cheese factories.
- In order to better gauge the health risk to consumers, safety questions on this type of bacteria should also be clarified.