Ochratoxin A (OTA) production by Aspergillus carbonarius in solid substrate fermentation

Mycotoxins are secondary metabolites produced by fungi that cause health issues; therefore, efficient, reliable, and cost-effective detection procedures are prioritized and welcomed by the agrifood sector to ensure public health and animal welfare. Mycotoxin standards with analytical purity are indispensable regardless of the method/device used in analyses. Ochratoxin A (OTA) production capacities of 73AspergillussectionNigriisolates were investigated. All A. carbonarius and 62% of A. niger isolates were ochratoxigenic, whereas A. japonicus isolates showed no toxin production. For the solid substrate fermentation (SSF),A. carbonariusM-A-0032, producing 17,432 µg kg⁻¹ OTA in Yeast Extract Sucrose (YES) medium, was selected. A preliminary trial showed that extraction with methanol:water (7:3) using a magnetic stirrer for 30 min was adequate. Rice and wheat were used as substrates, and OTA amounts were examined during 3-10 days at 26°C. Rice was superior to wheat as a substrate, and 40% moisture content was superior to 30%. Although OTA levels were highest on days 7 and 10, a 5-day incubation was considered sufficient. In the next trial, low-quality and broken rice were tested; after 5 days at 40% moisture content, rice produced 2,698.3 µg kg⁻¹ OTA, while broken rice produced 2,264.2 µg kg⁻¹. However, this may not have increased efficiency, as it affected gas and moisture transfer. The extraction of lower quality rice moistened with 40% for 5 days is sufficient to achieve the OTA concentration for scale-up as another round of the project.