Effects of atmospheric conditions, NaCl and pH on growth and interactions between moulds and yeasts related to blue cheese production.

The starter culture Penicillium roqueforti, undesired cultures Penicillium caseifulvum and Geotrichum candidum and the potential starter culture Debaryomyces hansenii were examined for their growth and interactions at environmental conditions similar to the Danish blue cheese Danablu. The combined effect of low oxygen (0.3%) and high level of carbon dioxide (25%) at 4% NaCl w/v (a(w) 0.97) and pH 4.5 and 6.5 on radial growth was examined on a cheese medium at 10 degrees C. P. roqueforti and G. candidum were well adapted to growth at low levels of oxygen and high levels of carbon dioxide but G. candidum was not able to grow in the presence of 4% NaCl (w/v). Growth of P. caseifulvum was strongly inhibited at atmospheric conditions comprising 25% carbon dioxide, especially in combination with 0.3% oxygen. Generally D. hansenii showed strong growth at all environmental conditions examined, except at 0.3% oxygen combined with 25% carbon dioxide and 4% NaCl (w/v). Growth and sporulation of P. roqueforti was highly affected in the presence of G. candidum at 25% carbon dioxide irrespective of levels of oxygen and NaCl in the cheese media. P. caseifulvum caused a pronounced inhibitory effect towards growth of P. roqueforti and D. hansenii at 21% oxygen. D. hansenii caused weak inhibition of P. roqueforti at 21% oxygen, while positive interactions between the two species were indicated at 25% carbon dioxide and 0.3% oxygen.