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Biodiversity and anti-listerial activity of surface microbial consortia from limburger, reblochon, livarot, tilsit and gubbeen cheese.

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The beauty of a smear cheese is skin deep

Smear ripened cheeses can be host to Listeria bacteria and so pose a potential health threat to the consumer. Researchers isolated and identified 900 yeast and bacteria on the surface of a European cheese that may help combat this food spoilage microbe.

Health

Pungent, piquant, spicy and yeasty - all descriptions of tastes of smear ripened cheeses. This attack on the taste buds is partly due to the microbial flora present on the surface. Luckily for the manufacturer, these microbes can also ward off undesirable bacteria. To help producers choose the correct microbes, the EU-funded project SCM characterised the bacteria and fungi on one of Europe's gourmet cheeses, Livarot. Named after a village in Normandy, this earthy cheese is one of the oldest cheeses in the region. Tests to confirm the microbes' identity used both physiological characteristics and their molecular fingerprints. Techniques included the polymerase chain reaction to produce millions of copies of the microorganisms' DNA in just two hours. The dynamics of this vast number of populations of microbes turned out to be incredibly complex. As each strain of bacteria or yeast becomes more dominant, it takes its toll on its neighbours through physical competition for space and nutrients combined with chemical attacks from antibiotics they produce. Throughout the ripening process, the dominant species changed, so much so that, for example, the yeast Kluyveromyces lactis appeared only at the beginning and then suffered virtual extinction. Another yeast species, Yarrowia lipolytica was found only at the end of the process. At any point during the three sampling times from the three dairies, the population structures were found to be different. Not only that but each dairy had its own characteristic flora, important for that unique taste so often associated with a particular producer. As taste and texture are linked to the microbial makeup of a cheese, producers can modify a cheese to order by simply changing its microorganisms. Cheese manufacturers and dairies will be more able to meet consumer demand as well as avoid unwelcome contamination.

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