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Prevent germination and growth by gas-forming bacteria in high-pH cheeses.

Clostridium tyrobutyricum is believed to be the major cause of the late blowing defect in high-pH cheeses such as Gouda and Edam. This defect is caused by the fermentation of lactate and the resulting production of gas and malodorous butyric acid. There are a variety of techniques for enumerating endospores of C. tyrobutyricum in milk. Most of these methods are relatively non-specific, enumerating a variety of Clostridium spp. capable of fermenting lactate and producing gas. Alternatively, qualitative methods using DNA probes are available to determine if C. tyrobutyricum is present.

Using a quantitative most-probable number method, scientists at the University of Wisconsin (Department of Food Science, 1605 Linden Dr., Madison, WI 53706) surveyed 21 pasteurized milk samples obtained from eight different cheese plants in Wisconsin. Numbers of endospores of lactate-fermenting, gas-producing Clostridium spp. never exceeded a concentration of 10 endospores/ml, but at least 1 endospore/50 ml was present in all samples.

Further evaluation of 14 milk samples showed, however, that most of these endospores were produced by Clostridium spp. other than C. tyrobutyricum. Investigators characterized 33 isolates obtained from the milk samples. Five isolates were identified as C. tyrobutyricum. Of 24 Clostridium isolates tested, all but one produced significant amounts of gas during the ripening of Gouda cheese after the inoculation of high concentrations of endospores.

The most discriminating technique for differentiating among the C. tyrobutyricum isolates, as well as the other 28 non-tyrobutyricum Clostridium spp., was the gas chromatographic analysis of cell membrane fatty acids.

It appears that low concentrations of endospores produced by lactate-fermenting, gas-producing Clostridium are present in certain milk that is used to make cheese. The majority of these endospores are not C. tyrobutyricum. But in high concentrations they may still produce deleterious amounts of gas during the ripening of high-pH cheeses. Further studies are needed to examine how cheese-ripening conditions or the centrifugation of milk may prevent germination and growth by these Clostridium spp.

Further information. Steven Ingham; phone: 608-265-4801; fax: 608-262-6872.
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Publication:Microbial Update International
Date:Dec 1, 1998
Words:329
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