Ochratoxin A and citrinin production by Penicillium verrucosum on cereal solid substrates

Cereals are among the most vulnerable substrates to mycotoxin contamination. One of the major fungal species colonising the ecosystem of stored grain is Penicillium verrucosum because of its ability to produce ochratoxin A (OTA). Knowledge of favourable environmental conditions promoting fungal growth and mycotoxin biosynthesis seems to be a crucial step towards preventing mycotoxin formation in stored grain. The aim of the study was to examine the effect of temperature and different cereal substrates (wheat, triticale, rye, barley, maize, rice) on fungal growth and OTA and citrinin (CIT) production by a mycotoxin-producing P. verrucosum strain at one moisture content. The correlation between fungal growth and mycotoxin biosynthesis was also investigated. For this purpose, cereal substrates moistened, autoclaved and inoculated with P. verrucosum spores were stored at 10°C, 20°C and 30°C for 40 days. After the storage period, the ergosterol (ERG) content as a fungal growth biomarker and OTA and CIT levels were determined using HPLC. Fungal growth was observed on all cereals at each temperature. Maximum ERG levels were found at 30°C and the values ranged from 401 to 3280 mg kg ⁻¹ of grain. Among tested cereals, the highest ergosterol content was found on rice at all applied temperatures. Accumulation of OTA and CIT was detected in samples stored at 20°C and 30°C, while optimal conditions for the production of both mycotoxins were observed at 20°C. The maximum concentration of OTA (31.9 ± 4.3 (SD) μg kg ⁻¹) and CIT (74.8 ± 5.7 μg kg ⁻¹) were found on rice. The ability to biosynthesise OTA and CIT at 10°C was not detected. Analysis of variance showed that single factors, temperature and cereal matrices and their interactions had significant effects on ERG, OTA and CIT levels. Optimal conditions for fungus growth did not coincide with the ones for mycotoxin formation.