Ochratoxin A and citrinin loads in stored wheat grains: Impact of grain dust and possible prediction using ergosterol measurement

Crop storage should be carried out under hygienic conditions to ensure safe products, but sometimes grain dust which has settled from previous storage may be left over and incorporated to the following stored grains. This paper describes the results obtained using a lab model developed in order to assess the impact of grain dust incorporation for its direct contribution as a contaminant but also as an inoculum in stored wheat. Settled grain dust ( 4 samples) released from Belgian grain storages were collected and analysed by HPLC for ergosterol, ochratoxin A (OTA) and citrinin (CIT) content. For OTA and for ergosterol, there was a high degree of variability in concentrations found in the dust samples ( from 17.3 - 318 ng g(-1) and from 39 - 823 mu g g(-1), respectively) whilst for CIT, the range was less significant ( from 137 - 344 ng g(-1)). Incorporation of grain dust into wheat storage contributed to an increase in the concentrations of mycotoxins in the stored grain. Dust acts as a contaminant and as an inoculum. According to these two ways, patterns of mycotoxin generation vary with the nature of the mycotoxin, the mycotoxigenic potential of dust and the water activity of the wheat. OTA and CIT showed a very versatile image when considering the amounts of toxins produced under the selected experimental conditions. The development of a robust tool to forecast the mycotoxigenicity of dust was based on the determination of ergosterol content as a general marker of fungal biomass. Present results suggest that this predictive tool would only be valid for predicting the contamination level of CIT and OTA at reasonable moisture content ( 14 - 20%). The potential risk of having highly contaminated batches from stock to stock may thus occur and this paper discusses possible pathways leading to OTA and CIT contamination either under wet or dry storage conditions. We therefore, recommend taking precautionary measures not only by controlling and maintaining moisture at a reasonable level during storage of the raw materials but also by paying more attention to the cleaning of the stores before loading in the new harvests.