The combined effects of water activity (aw) and temperature on growth of and penicillic acid (PA) production by strains of Penicillium cyclopium, Penicillium martensii, and Aspergillus ochraceus were determined. On malt agar media in which the aw had been adjusted by addition of sucrose or glycerol, the minimum aw for PA production by P. cyclopium and A. ochraceus was 0.97 and that of P. martensii was 0.99. The temperature range for PA production by P. cyclopium and P. martensii was 4–31 C, whereas that of A. ochraceus was 8–31 C. Optimum temperature for PA production by P. cyclopium and A. ochraceus varied with the strain tested and was 24–31 C. The only strain of P. martensii tested showed an optimum temperature of 16–24 C. On Gouda and Tilsiter cheese of 0.96–0.98 aw, temperature ranges for growth of P. cyclopium, a common mold on cheese, were 0–24 and 4–16 C, respectively. When a strain of P. cyclopium known to be able to produce PA in culture media, was grown on Gouda cheese incubated at different temperatures, no PA was detectable in the moldy cheese at the time the average colony diameter was 30 mm. However, in a culture on Gouda cheese incubated for a prolonged time (42 days) at 16 C, PA was detectable. On poultry feed, A. ochraceus produced PA aw as low as 0.88, whereas the minimum aw for PA production by P. cyclopium was 0.97.
1Laboratory for Zoonoses and Food Microbiology.
2Laboratory for Chemical Analysis of Foodstuffs.