Yeasts and Molds: Penicillium roqueforti

Penicillium roqueforti is used as a fungal starter culture for the production of a number of blue-veined cheeses, with both proteolytic and lipolytic enzymes produced by the fungus involved in cheese ripening and flavor production. The fungus has the lowest oxygen requirements for growth of any Penicillium species. It is also a psychrophile and grows vigorously at temperatures as low as 4. °C, but not above 35. °C. Many P. roqueforti strains are known to be very tolerant to weak acid preservatives, being able to grow in the presence of 0.5% acetic acid and in the presence of 9000. ppm sorbate. Growth of the fungus is stimulated at low salt concentrations, with 1% salt (NaCl) being the concentration with the highest stimulating effect. Penicillium roqueforti strains isolated from Blue cheeses are known to produce both the mycotoxins PR toxin (7-acetoxy-5,6-epoxy-3,5,6,7,8,8. a-hexahydrocarboxaldehyde) and roquefortine, which have also been shown to be present in cheese. They are however not thought to pose a significant health risk to consumers as they are quite unstable in cheese. Nonetheless, it is preferable from a food safety perspective to use P. roqueforti strains that do not produce secondary metabolites or mycotoxins as starter cultures in cheese manufacturing. DNA-based molecular techniques have been developed and applied in the detection and identification of Penicillium species employed in cheese manufacture.