Submitted to: United States-Japan Cooperative Program in Natural Resources
Publication Type: Abstract Only
Publication Acceptance Date: 11/3/2007
Publication Date: 11/3/2007
Citation: Voss, K.A., Burns, T.D., Riley, R.T., Snook, M.E., Mitchell, T.R. 2007. Fumonisin concentrations and in vivo toxicity after nixtamalization of corn culture material: evidence for fumonisin-matrix binding. United States-Japan Cooperative Program in Natural Resources. November 3 - 10, 2007. Tokyo and Okinawa, Japan. Interpretive Summary: Abstract - no summary required.
Technical Abstract: Fumonisins are found in corn and corn-based foods. Fumonisin B1 (FB1), the most common fumonisin, is toxic to a variety of species, is carcinogenic to rats and mice, induces neural tube defects in mice and is considered a possible risk factor for neural tube defects and cancer in humans. Minimizing exposure is therefore desirable. Nixtamalization cooking involves steeping corn in alkaline water. It reduces (detectable) FB1 concentrations in the cooked corn, however, the degree of reduction might be overestimated, and toxicity of the nixtamalized corn underestimated, if undetectable FB1-corn matrix reaction products are formed. To investigate this possibility, F. verticillioides culture material (CM) was nixtamalized as is (NCM) or after being mixed with ground corn (NCMC). Additional amounts of CM were sham (nonalkaline conditions) nixtamalized without (SCM) or with ground corn (SCMC). CM equivalents of the unprocessed CM, NCM, NCMC, SCM or SCMC were blended with basal diet and fed to male rats for one (n=3) or three (n=5) weeks. Control groups were fed basal diet into which uncontaminated corn (UC) or nixtamalized UC (NUC) had been added. Nixtamalization and sham nixtamalization reduced measurable (by HPLC) FB1: its concentrations in the blended CM, NCM, and SCM diets were 9.1, 2.1, and 1.2 ppm, respectively. Mixing the CM with corn prior to nixtamalization further decreased FB1 concentrations in the blended diet (NCMC diet = 0.5 ppm) whereas the corn had no effect on FB1 concentration during the sham procedure (SCMC diet = 1.0 ppm). FB1 concentrations in the UC and NUC diets were < 0.2 ppm. No differences in body weight, food consumption or relative kidney weight were found in the feeding bioassay. Microscopic kidney lesions of moderate severity and exhibiting widespread apoptotic tubule cells were found in the group fed the unprocessed CM. Nixtamalization was beneficial as the lesions in the rats fed NCM were significantly reduced in intensity and markedly fewer apoptotic cells were found. However, apoptosis counts in kidney of the NCM-fed rats were > 2.5 (at week 3) to > 5 fold (at week 1) higher than those of the NCMC and other remaining groups. The renal concentrations of free sphinganine (Sa) and its 1-phosphate metabolite (biomarkers of fumonisin exposure) were determined to further evaluate exposure and toxicity. The results confirmed that the presence of corn enhanced toxicity reduction by nixtamalization: (a) total Sa (Sa plus Sa 1-phosphate) concentration of the CM group (600 – 800 nmol/g) was higher than the NCM group (400-600 nmol/g); (b) the latter was in turn higher than the SCM and SCMC groups (30-90 nmol/g); and (c) the lowest concentrations were found in the NCM, UC and NUC groups (< 8 nmol/g). Together, these results indicate that the presence of corn matrix during cooking enhanced the reductions in FB1 toxicity achieved when nixtamalizing F. verticillioides CM and provide indirect evidence suggesting that FB1-corn matrix interactions contributed to this protective effect.