The involvement of Clostridium tyrobutyricum in gas production in brined-cheeses such as Gouda and Grana Padano has been well established. However, this clostridium would not normally be expected to cause problems in Cheddar cheese of satisfactory salt, acid and moisture content⁷. Some homofermentative bacteria e.g. Lactobacillus casei, and Lactococcus lactis ssp. lactis biovar. diacetylactis can produce CO₂ from citrate and have been implicated in the blowing of film-wrapped cheese⁸. The potential for gas production by heterofermentative lactobacilli has been known since the work of Sherwood⁹. Coliforms are usually only a problem when the starter fails, due to bacteriophage infection or antibiotic residues in milk. Under certain conditions, urease producing strains of Streptococcus thermophilus can produce gas in Cheddar cheese ¹⁰. Since Streptococcus thermophilus can grow in the regeneration section of pasteurisers relatively high levels of this thermophile may occasionally occur in pasteurised milk. Sherwood⁹ first established that the addition of leuconostocs to milk for Cheddar cheese manufacture gave rise to gas and open texture in the cheese. Because of their sensitivity to salt and high acidity propionibacteria would not be expected to produce gas in Cheddar cheese. Examination of the gas produced by the major gas-producing organisms (Table 1) indicates that the identification of the gas present in blown cheese may have value in identifying the gas producing species.

PROBLEMS ASSOCIATED WITH MICROBIOLOGICAL STUDIES OF "GASSY" CHEESE

Determination of the causal agent(s) of gas production in cheese can be difficult. The numbers of the micro-organism concerned may have declined to a low, apparently insignificant level at sampling. This can be overcome by serial sampling during maturation. Some micro-organisms are not distributed uniformly in cheese, for example lactobacilli may be found in fissures or curd junctions. Sampling schemes should be designed to take account of the potential for non-random distribution of the gas producing agent

The selective agar media used may be inadequate; e.g., some leuconostocs and pediococci will form colonies on Rogosa agar originally developed for work with lactobacilli³. Certain media may allow the growth of starter lactococci.

Microscopic studies of 'gassy' cheese can also yield inconclusive results. Leuconostocs, for example, may appear as small rods, cocco-bacilli or cocci. Heterofermentative lactobacilli may also appear as cocco-bacilli

Where a particular micro-organism is suspected of being the causal agent, current molecular biology techniques involving polymerase chain reaction (PCR) amplification of DNA sequences combined with species-specific DNA probes can be used to confirm the identify of the micro-organism. Klijn et al.¹² have used PCR and a species specific-DNA probe to confirm Cl. tyrobutyricum as the causative agent of late blowing in experimental cheese.

MAJOR CAUSAL AGENTS OF UNWANTED GAS PRODUCTION IN CHEESE
PROBLEMS ASSOCIATED WITH MICROBIOLOGICAL STUDIES OF "GASSY" CHEESE
MICROBIOLOGICAL STUDIES OF INCIDENTS OF EARLY GAS PRODUCTION IN COMMERCIAL CHEESE PLANTS
CONTROL OF GAS PRODUCTION IN CHEESE
REFERENCES



How to cite this article

Mullan,W.M.A. (2003).  [On-line] UK:Available:
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