Submitted to: Food and Chemical Toxicology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 20, 2008
Publication Date: June 1, 2008
Repository URL: http://hdl.handle.net/10113/25721
Citation: Burns, T.D., Snook, M.E., Riley, R.T., Voss, K.A. 2008. Fumonisin concentrations and in vivo toxicity of nixtamalized Fusarium verticillioides culture material: evidence for Fumonisin-matrix interactions. Food and Chemical Toxicology. 46:2841-2848. Interpretive Summary: Fumonisin B1 (FB1) is a fungal toxin found in corn and corn-based foods. It is toxic to animals and might increase the risk of birth defects or cancer in humans. Minimizing exposure is therefore desirable. Nixtamalization is a cooking method that involves cooking and steeping corn under basic conditions. Nixtamalization reduces the amount of FB1 in the cooked corn, however, the extent of reduction might be underestimated if unknown FB1 reaction products form during cooking. A bioassay-based approach was used to investigate this possibility. Corn contaminated with FB1 (called culture material or CM) was nixtamalized by itself or after mixing it with clean corn. Sham nixtamalizations, done under nonbasic conditions, of the CM and CM mixed with corn were also done. Uncooked CM, the nixtamalized and sham nixtamalized materials, and control corn were mixed into rodent diets, FB1 in the diets measured, and the diets then fed to rats for three weeks. Toxicity was evaluated by microscopically examining the kidneys and measuring specific biochemical changes of the type caused by FB1. Compared to the uncooked CM, the amount of FB1 in the diet made with the nixtamalized CM was reduced about 80 percent. Greater reductions of up to 95% compared to the uncooked CM were achieved when the CM plus corn mixture was nixtamalized. The presence or absence of corn did not affect the amount of FB1 reduction achieved, about 90% compared to uncooked CM, during sham nixtamalizations. Significant microscopic and biochemical kidney effects were found in the rats fed the uncooked CM. The effects were less severe in rats fed the nixtamalized CM whereas the appearance of biochemical profiles of the kidneys of the remaining groups, including the group fed the nixtamalized CM plus corn mixture did not differ from the control groups. Together, these results show that the presence of corn during cooking enhanced the protective effect of nixtamalization. The beneficial chemical reactions occurring between FB1 and the corn during nixtamalization should be identified.
Technical Abstract: Fumonisin B1 is a Fusarium mycotoxin found in corn and corn-based foods. It is toxic to animals and evidence suggests that it is a risk factor for neural tube defects and cancer in humans. Minimizing exposure is therefore desirable. Nixtamalization involves cooking and steeping corn in alkaline water. It reduces FB1 concentrations in foods, however, reductions might be overestimated and potential toxicity underestimated if undetectable FB1-corn matrix reaction products are formed. F. verticillioides culture material (CM) was nixtamalized as is (NCM) or after being mixed with ground corn (NCMC). CM was also sham nixtamalized (nonalkaline conditions) without (SCM) or with corn (SCMC). Toxicity was assessed by microscopic examination of the kidneys and quantification of renal sphinganine (Sa) and Sa 1- phosphate of rats fed CM equivalent weights of the CM, NCM, NCMC, SCM or SCMC for one (n=3) or three (n=5) weeks. Control groups were fed diets containing unprocessed (UC) or nixtamalized (NUC) uncontaminated corn. Both nixtamalization and the sham procedure reduced FB1: the CM, NCM, and SCM diets contained 9.1, 2.0, and 1.2 ppm, respectively. The presence of corn further decreased FB1 concentrations during nixtamalization (NCMC diet = 0.5 ppm) whereas the corn had no effect on FB1 concentration during the sham process (SCMC diet = 1.0 ppm). Moderate kidney lesions with widespread apoptosis were found in the group fed CM. Significantly less severe lesions were found in the NCM group whereas no lesions were found in rats fed the NCMC, SCM, SCMC, UC or NUC. Kidney Sa and Sa 1-phosphate findings revealed a similar pattern: the kidney concentrations of Sa plus Sa 1-phosphate decreased in the order: CM group (600 – 800 nmol/g) > NCM group (400-600 nmol/g) > SCM and SCMC groups (30-90 nmol/g). Lowest concentrations (< 8 nmol/g) were found in the NCM, UC and NUC groups. These results indicate that the presence of corn matrix during cooking enhanced the reductions in FB1 bioavailability and toxicity achieved by nixtamalization of F. verticillioides CM and further suggest that FB1-corn matrix interactions contributed to this protective effect.