Ochratoxin A (OTA) Production By Aspergillus fresenii and Aspergillus sulphureus on Niger Seeds

Introduction:  Mycotoxin contamination of foods and feeds poses a high risk for human and animal health. Ochratoxin A (OTA) is a ubiquitous mycotoxin produced by Aspergillus and Penicillium fungi. It exhibits nephrotoxicity, teratogenicity, mutagenicity, and immunotoxicity in both humans and animals. Niger (Guizotia abyssinica) is an oil seed that is used for extracting cooking oil, an animal feed in countries like Ethiopia and India, and an export to Europe and North America. It has, also, been implicated in high level of mycotoxin contamination. To our knowledge, there have been no studies on the production of OTA on niger seeds. In this study, the environmental conditions that support OTA production have been investigated.

Purpose:  This study was conducted to determine the effects of water activity, temperature, and incubation time on OTA production by Aspergillus fresenii and Aspergillus sulphureuson on niger seeds.

Methods:  Fungi were grown in Czapek Yeast Extract agar (CYA), individually, at 30^oC for 5 days. Ten μl spore suspensions were used to inoculate two grams of sterilized seeds placed in each Petri dish (12 plates/species), adjusted to different water activity (a_w) values (0.90, 0.94, and 0.98). Plates were incubated at 20, 25, 30, and 35^oC for 5 or 10 days. After extraction of the seeds from each plate, using 70% methanol in water, the OTA was quantified by enzyme linked immunosorbent assay (ELISA). Limit of quantitation was 0.4 μg/kg.

Results:  Both fungi growth and OTA production were highly influenced by water activity and temperature. The highest OTA production (166 μg/kg) was observed at 35^oC, 10 days incubation, and 0.98 a_w. Linear regressions showed that temperature was a statistically significant predictor of OTA values (P = 0.022). The coefficient for temperature was 3.93 (95% confidence interval).

Significance: Our studies will help understand the conditions that are important to minimizing contamination of niger seeds with OTA.