Smear Cheese Project Progress Summary (2001 – 2002)

Objectives

To (1) identify yeasts from the surface of 5 European cheeses, which have anti-listerial activity and evaluate them commercially for their ability to inhibit listeria in commercial cheese and (2) to determine the species of bacteria and yeast present on the surface of the cheese using classical and molecular techniques.

Results and Milestones

This project has been operating for one year during which more than 2000 bacterial and 2000 yeast isolates have been made from the 5 cheeses. In addition, more than 1200 bacteria and yeast from previous studies have been added to the collection. PyMS was not satisfactory for dereplicating all the bacteria but RepPCR was effective. The Gubbeen isolates were dereplicated by PFGE and showed that Corynebacterium casei, C. mooreparkense, C flavescens, M. gubbeenense, a B. linens type organism and Staphylococcus species were present in most cheeses but there was considerable differences in the relative proportions of the different species in each batch. Several coryneform and staphylococci have to be identified but all the staphsylococci were coagulase negative and so were not Staph. aureus. DGEE was shown to very useful in detecting bacteria on the surface of the cheese.

FTIR was used to dereplicate the yeasts. The results showed that the dominant yeast in Tilsit cheese is D. hansenii, (69% of isolates), in Gubbeen, D. hansenii and C. catenulata (49 and 33% of isolates respectively) dominated followed by considerable members of Clavispora lusitaniae (16% of isolates) while in Livarot, Geotrichum candidum followed by D. hansenii and Yarrowia lipolytica dominated (61, 12 and 11% of isolates respectively).

Considerable difficulties emerged in trying to develop a screening test to detect anti-listerial activity in the yeast but we are confident that we have solved them.

Benefits and Beneficiaries

The major practical result from this project will be the identification of anti-listerial yeast. Toward the end of the project, these yeast will be evaluated by 4 commercial cheese producers to determine that they have no effect on the appearance, texture or taste of the cheese. The results of these trials will form the basis of a workshop called which will be held in association with the final project meeting and to which representatives of all the EU smear-cheese manufacturers will be invited.

It is generally considered that B. linens is the dominant organism in bacterial surface-ripened cheese. It is expected that several new species of yeast and bacteria will be identified on these cheeeses which have never been extensively studied and compared with each other.