Beyond the visible lesion: mycotoxin attenuation and spatial heterogeneity in maize cobs

Visible mould is widely used as a practical sorting cue in maize, but it remains unclear whether the visible lesion marks the boundary of mycotoxin contamination within an intact cob. This study examined mycotoxin attenuation, spatial heterogeneity, and co-occurrence in visibly mouldy white maize cobs, using measured distances from the visible mould margin. Cobs with visible mould (n = 35) were sampled for the study. For each cob, the visible mould margin was coded as 0 mm, and adjacent sections were collected at the 50% and 75% points along the measured distance from the lesion boundary to the distal cob tip, resulting in 98 cob-section observations. Mycotoxins, FUMs (FB1, FB2, FB3), deoxynivalenol (DON), zearalenone (ZEA), nivalenol (NIV) and AF (AFB1) were quantified by liquid chromatography tandem mass spectrometry. Samples with no detectable levels of mycotoxins were replaced with zero, and total FUMs were calculated (FB1 + FB2 + FB3). The visible mould margin accounted for the largest share of the measured toxin burden, accounting for 84.4% of total FUM, 89.4% of DON, 77.8% of ZEA, and 92.2% of NIV. Adjacent sections retained measurable residual mycotoxins, including 15.6% of total FUM, 10.6% of DON, 22.2% of ZEA, and 7.8% of NIV. In full-distance models, DON, ZEA, and NIV declined significantly with distance, whereas total FUM did not show significant monotonic attenuation. The AFB1 was detected in only three cob sections; these detections co-occurred with Fusarium-associated toxins. Co-occurrence analysis showed that adjacent sections frequently remained positive for multiple Fusarium-associated toxin groups, with the FUM + DON + ZEA profile persisting across measured-distance bands. These findings show that visible mould is a useful warning signal but not a reliable toxicological boundary. The results support cob-level rejection or segregation of visibly mouldy cobs before shelling, rather than lesion-level trimming, as a more defensible food-safety control measure.