The effects of milling and processing on wheat contaminated with ochratoxin A

Samples of sound home-grown wheat (one hard and one soft milling) were obtained, cleaned, and gamma-irradiation used to reduce numbers of viable naturally-occurring fungi. Each sample was inoculated with a toxigenic strain of Penicillium verrucosum and monitored for ochratoxin A formation. When ochratoxin A had reached a level of 60 micrograms/kg, the samples were milled into ten fractions which were analysed for ochratoxin A by an HPLC method with immunoaffinity column clean-up. Each straight-run white flour was baked into bread which was analysed in the same way. Relationships between ochratoxin A levels in naturally-contaminated wheat and the products of milling and baking were established. The recovery of ochratoxin A in wholemeal compared with the cleaned wheat was essentially complete and no significant loss occurred on baking white or wholemeal flour into bread. Recoveries in the straight-run white flours, however, were only approximately one-third for the hard wheat and two-thirds for the soft wheat of the ochratoxin A in the uncleaned wheat. The reason for this was that a much higher proportion of the ochratoxin A was found in the bran and offal fractions from hard wheat than from soft. Conversely, a much higher proportion of the ochratoxin A was found in the reduction flour from soft wheat than from hard. Scouring was examined as a possible method of decontamination of wheat prior to milling. This process removes a proportion of the pericarp (bran coat) prior to milling. The results of the study confirmed that scouring reduced the ochratoxin A level in white and wholemeal flour three-fold for both the hard and soft wheat.