Ochratoxin A Production by Some Fungal Species in Relation to Water Activity and Temperature

The effects of water activity (a_w) and temperature on growth of and ochratoxin A (OA) production by strains of Aspergillus ochraceus , Penicillium cyclopium , and Penicillium viridicatum were investigated. On agar media in which the a_w had been adjusted by addition of sucrose or glycerol, the minimum a_w values for OA production by A. ochraceus , P. cyclopium and P. viridicatum lay between 0.83-0.87, 0.87-0.90, and 0.83-0.86, respectively. At 24 C, optimum a_w values for OA production by A. ochraceus and P. cyclopium were 0.99 and 0.95-0.99, respectively, whereas that of P. viridicatum varied and was 0.95 and 0.99 for the two strains tested. At optimum a_w, the temperature range for OA production by A. ochraceus was 12-37 C, whereas that of P. cyclopium and P. viridicatum was 4-31 C. Optimum temperature for OA production by A. ochraceus was 31 C, whereas that of P. cyclopium and P. viridicatum was 24 C. On Edam cheese of 0.95 a_w the minimum temperature for OA production by P. cyclopium was 20 C. On barley meal, P. viridicatum produced maximal quantities of OA at 0.97 a_w and could produce OA at temperatures as low as 12 C.