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Nixtamalisation is a widely used food processing method in which whole kernel corn is cooked and steeped in alkaline water. It reduces the amount of fumonisin B1 (FB1) that can be detected after cooking. However, the fate of FB1during nixtamalisation is not fully understood and potentially toxic reaction products, including matrix-associated “masked” FB1forms that are not detected by routine analytical methods might remain in nixtamalised corn. To assess how nixtamalisation of whole kernel corn affects fumonisin toxicity, male rats were fed diets containing low, mid or high levels of uncooked (LU, MU, HU) or alkaline cooked (LC, MC, HC) FB1-contaminated corn for 3 weeks. The control diet contained uncontaminated corn only. Apoptotic kidney lesions of the type caused by FB1were not found in the LC or MC groups. Lesions in the group fed HC were minimal and less severe than those found in the rats fed LU, MU or HU. Furthermore, significantly increased sphinganine and sphingosine concentrations indicative of FB1exposure were found in the kidneys of the rats given LU, MU or HU. Concentrations were also elevated, but to a lesser extent, in rats fed HC, whereas sphinganine and sphingosine concentrations in rats given LC or MC did not differ from the control group. FB1concentrations in the LC (0.08 mg kg−1), MC (0.13 mg kg−1) and HC (0.37 mg kg−1) diets were markedly reduced compared with their LU (1.8 mg kg−1), MU (3.5 mg kg−1) and HU (4.2 mg kg−1) counterparts as determined by HPLC (n =  1 analysis/diet). Taken together, the findings show that nixtamalisation is an effective cooking method for reducing the potential toxicity of FB1contaminated corn. [ABSTRACT FROM PUBLISHER]