TOXICOLOGY AND TOXINOLOGY OF MYCOTOXINS IN FOODS
Location: Toxicology and Mycotoxin Research
Title: Alkaline cooking (nixtamalisation) and the reduction in the in vivo toxicity of fumonisin-contaminated corn in a rat feeding Bioassay
Submitted to: Food Additives & Contaminants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 10, 2012
Publication Date: N/A
Interpretive Summary: Fumonisins are fungal toxins that are common in corn and corn-based foods. They are suspected risk factors for birth defects and cancer. Alkaline cooking, or nixtamalization, of corn is used to make masa and tortilla products and it reduces the amount of fumonisins found in the cooked products using routine analysis methods. However, corn and corn-based foods can also contain "masked" fumonisins. These are food matrix-associated forms that are not measured by conventional methods and, if liberated during digestion, would increase fumonisin exposure. Because the amounts of "masked" fumonisins that occur in alkaline cooked foods are not known, conventional chemical analyses could underestimate toxicity of alkaline cooked corn. To test if this is the case, three batches of corn containing low-, mid-, or high- levels of fumonisins were nixtamalized, mixed with a standard rodent ration, and fed to groups of rats for three weeks. Additional groups were fed equivalent amounts of the uncooked low-, mid-, or high-level corn or a control diet. The three diets made with uncooked contaminated corn caused kidney pathology and biochemical effects that are characteristic of fumonisin exposure. The effects were partially reversed in the group fed the high-level nixtamalized corn and totally reversed in the groups fed low-level or mid-level nixtamalized corn. Therefore, alkaline cooking (nixtamalization) effectively reduces the toxicity of fumonisin contaminated corn.
Nixtamalization is a widely used food processing method in which whole kernel corn is cooked and steeped in alkaline water. It reduces the amount of FB1 that can be detected after cooking. However, the fate of FB1 during nixtamalization is not fully understood and potentially toxic reaction products, including "masked" FB1 (matrix-associated), that are not detected by routine analytical methods, might remain in nixtamalized corn. To assess how nixtamalization 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 three weeks. The control diet contained uncontaminated corn only. Apoptotic lesions of the type caused by FB1 were not found by microscopic examination of the kidneys from 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 FB1 exposure 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. FB1 concentrations in the LC (0.08 mg/kg), MC (0.13 mg/kg), and HC (0.37 mg/kg) diets were markedly reduced compared to their LU (1.8 mg/kg), MU (3.5 mg/kg), and HU (4.2 mg/kg) counterparts as determined by HPLC (n=1 analysis/diet). Taken together, the findings show that nixtamalization is an effective cooking method for reducing the potential toxicity of FB1 contaminated corn.