Hard Swiss Cheeses – Approaching Safety

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International Association for Food Protection, Baltimore,MD, 14. – 17. August 2005

Hard Swiss Cheeses – Approaching Safety

Melchior Schaellibaum

Swiss Federal Research Station for Animal Production and Dairy Products

E-mail: Melchior.schaellibaum@alp.admin.ch

ABSTRACT

The ability of potentially pathogenic bacteria to grow and to survive during the

manufacture and ripening of Swiss hard and semihard cheese varieties made from raw milk was examined (see Figure 1 and 2). In Swiss hard cheeses, the inoculated

pathogens beyond 1 day were not detected. At the age of commercial ripeness, also the semihard cheeses were free from the inoculated pathogens and their toxic metabolites, except for L. monocytogenes, which survived the manufacturing and ripening process.

Based upon these knowledge the Swiss dairy industry runs a monitoring program for Listeria for cheese and other dairy products. Since its introduction, the program has proven to be a suitable instrument for identification and management of L.

monocytogenes contamination at every stage of cheese production, ripening, and distribution.

The decrease of the pathogens can be explained by the synergistic effects of a high milk quality, short milk storage (effect of active antimicrobial enzyme systems of fresh raw milk), antagonistic starter culture flora , fast acidification, antimicrobial effect of lactic acid, high curd cooking temperatures, intense brining, and the ripening at elevated temperatures for at least two months. All these factors are also important determiants of flavour and texture quality. It can be concluded, that there is no contradiction between authentic flavours and hygienic safety (Bachmann and Spahr, 1995).

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0 1 2 3 4 5 6 7 8

Hard cheese (log cfu / ml, g)

0 1 2 3 4 5 6 7 8

Semihard cheese (log cfu / ml, g)

milk curd cheese cheese cheese cheese cheese after 1 d 7 d 30 d 60 d 90 d

cooking

Figure 1. Behavior of Aeromonas hydrophila (G), Campylobacter jejuni (‹), Escherichia coli (∆), Listeria monocytogenes (s), Pseudomonas aeruginosa ({), Salmonella typhimurium (l), Staphylococcus aureus (…), Yersinia enterocolitica („) during manufacture and ripening of hard and semihard cheeses made from raw milk (only data of batches with longest survival are shown). - - - detection limit (Bachmann and Spahr, 1995)

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0 30 60 90 120 150

0 1 2 3 4 5 6

0 30 60 90 120 150

Ripening days 0

1 2 3 4 5 6

lo g1 0 cf u/ g

Semi-hard cheese R

= 0.894

D-Value = 45.5

Hard cheese R

= 0.923 D-Value = 27.8

Figure 2. Inactivation curves for Mycobacterium avium subsp. paratuberculosis in hard cheese (Swiss Emmentaler) and semihard cheese (Swiss Tilsiter) during 120 days of ripening (Spahr and Schafroth, 2001)

REFERENCES

Bachmann H.P., Spahr U. 1995. The fate of potentially pathogenic bacteria in swiss hard and semihard cheeses made from raw milk. J.Dairy Sci. 78:476-483

Spahr U., Schafroth K. 2001. Fate of Mycobacterium avium subsp paratuberculosis in Swiss hard and semihard cheese manufactured from raw milk. Appl.Environ.Microbiol.

67: 4199-4205

Spahr U., Url B. 1994. Behaviour of pathogenic bacteria in cheese - a synopsis of experimental data. Bull.Int.Dairy Federation. 298:2-16