Ochratoxin A production during ambient-air drying

Abstract

Ochratoxin A (OTA) is a fungal mycotoxin that may form when grain moisture content exceeds 18%. EU food limits for unprocessed cereals are set at 5 μg/kg. A study was undertaken to provide data on the formation of OTA during ambient air drying at full scale.Four bins each holding 30 tonnes of wheat at a range of initial moisture contents were dried using ambient air in two successive seasons. In the second, the wheat was inoculated with Penicillium verrucosum spores at three levels. Physical parameters (e.g. moisture, temperature and air flow in the wheat) and biological changes including mycotoxin production were measured. Data on changes in populations of fungi in the wheat were also collected.OTA was found in the wettest treatments and not in the treatments with lower initial moisture content. Neither the presence nor the amount of OTA, or the counts of fungal colonies of P. verrucosum, showed any significant relationship to level of inoculum. This means that drying rate to avoid OTA does not need to depend on the amount of inoculum present. When drying by continuous ventilation, the risk of OTA appeared to be no greater than the risk of visible mould or significant loss of viability, and hence the time for the drying front to pass through the bed to achieve drying with low risk of OTA does not need to be reduced. Current recommendations given in the UK Grain Storage Guide for bed depth and airflow rate in drying by continuous ventilation remain appropriate.