Blue cheese contamination

Some microorganisms (such as Penicillium roqueforti) decar-boxylate sorbic acid to penta-l,3-diene, which causes an off-flavour (resembling kerosene) in cheeses (Figure 11.1). The threshold concentration of penta-1,3-diene is 1 mg/kg. Also reported are cases of contaminated margarines, fruit drinks, jams and marzipan, and similar products that used pure cultures of microbial strains (such as blue cheese and fermented dairy products). 

The fungus P, roqueforti is of interest to agricultural and food scientists owing to its use in the production of roquefort cheese and other blue cheeses. Roquefortine is a natural contaminant, as it was detected in all 16 samples of blue cheese that were produced in seven countries (Scott and Kennedy, 1976). Scott et al. (1977) reported that an optimum yield of roquefortine was obtained on cultivation of the fungus in a medium containing sucrose (15%) and yeast extract (2%) for 16 days at 25 C. 

Milk Substrates Cheese is perhaps the oldest of the fermented foods. (Fig. 1) The basic underlying microbial transformation in all cheese manufacture is the conversion of lactose of milk into lactic acid. The microorganisms in the starter culture contribute significantly to the flavor of the cheese. The secondary microbial flora of the cheese also elaborate taste and odor active substances. These organisms may be present as chance contaminants or introduced intentionally(8), and result in distinctive types of cheeses such as Cheddar, blue veined and Swiss. 

The fungus Penicillium roqueforti is used in the production of blue-veined Roquefort, Stilton and Gorgonzola cheeses. It contributes to the flavour of these cheeses by degrading medium-chain fatty acids to methyl ketones with one less carbon atom. The fungus is also a microbial spoilage contaminant of dairy products and it is found on some mouldy grains. There are several sub-species of... 

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