Smear Cheese Project Progress Summary (2002 – 2003)

Objectives

• To determine the surface microflora of 5 European smear-ripened cheeses.
• To establish the population dynamics of the surface microflöra
• To identify yeasts which have anti-listerial activity and evaluate them commercially

Results and Milestones

2 858 bacterial and 2 557 yeasts were isolated from the surface of the 5 cheeses at the early, middle and late periods of ripening and were reduced to 675 and 306 different strains, respectively, by RepPCR and PFGE (bacteria) and FTIR (yeasts). The bacteria were divided into 15 groups of closely related species by BOX-PCR and the dominant ones were Arthrobacter, Microbacterium, Corynebacterium, Brevibacterium and Staphylococcus species. New taxa have also been identified. The yeasts included 14 species with the dominant ones being Debaryomyces hansenii, Geotrichum candidum and Clavispora catenulata. Each cheese had a different surface flora. The results from the identification of the isolates were pretty much confirmed by DGGE.

A genus-specific primer was designed for Brevibacterium and species-specific ones for D. hansenii, G. candidum, Yarrowia lipolytica and Kluyveromyces lactis/marxianus. Cheese has been made with a large collection of yeasts and bacteria and evaluated for their aromatic and technological properties. Interactions between the yeast and bacteria producing the best flavoured cheeses will be studied by SSCP analysis and universal primers have been designed for this purpose. The development of other species-specific primers is on-going.

A screening method to determine the anti-listerial activity of yeast was developed and 58 out of 1944 strains of yeasts tested, inhibited at least 4 of the 5 strains of Listeria monocytogenes used as test or indicator strains. Some strains also inhibited growth of L- monocytogenes on Cheese Agar. These yeasts will be evaluated further on cheese in the next year.

Benefits and Beneficiaries

The collection of yeasts and bacteria from the 5 different cheeses throughout ripening is a huge resource of strains and it is hoped to house them in a central location. It is the first time that such a detailed analysis of the surface flora of different cheeses has been undertaken. The molecular and classical analysis has for the first time given a clear idea of the diversity of the surface microflora of these cheeses. The identification of yeast strains which inhibit L. monocytogenes is also a significant development.

Future Actions

It is hoped that some of the anti-listerial yeast will inhibit the growth of L. monocytogenes on the cheese surface and this will be evaluated in the next year.