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Title: Fumonisin concentration and ceramide synthase inhibitory activity of corn, masa, and tortilla chips

item Voss, Kenneth - Ken
item Norred, William
item Meredith, Filmore
item Riley, Ronald
item Saunders, D. Stephen

Submitted to: Journal of Toxicology and Environmental Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/19/2005
Publication Date: 7/1/2006
Citation: Voss, K.A., Norred, W.P., Meredith, F.I., Riley, R.T., Saunders, D. 2006. Fumonisin concentration and ceramide synthase inhibitory activity of corn, masa, and tortilla chips. Journal of Toxicology and Environmental Health. 69(14):1387-1397.

Interpretive Summary: Fumonisins are toxins produced by molds that grow on corn. They are found in corn-based foods. We have shown that nixtamalization, the process by which corn is made into masa for tortilla products, reduces the amount of fumonisin in the masa and tortilla products. However, there is emerging concern that chemical analysis might not account for all biologically active fumonisins in cooked foods and therefore underestimate toxicity of the products. We therefore re-evaluated the nixtamalization and tortilla making process, this time using a cell bioassay to compare the fumonisin-specific biological activity of corn extracts to extracts of nixtamalized products made from the corn. We found that the biological activity of the masa and tortilla product extracts were equal and did not differ from that of unexposed cells. In contrast, the biological activity of the corn extracts was similar to that of obtained when the cells were dosed with fumonisin. This indicates that the first step of nixtamalization, that is, cooking and steeping the corn in lime-water, reduces the fumonisin-like biological activity of masa and tortilla products. The magnitude of the reduction in biological activity was similar to the reduction in fumonisin concentration found by chemical analysis of the corn, masa and tortilla products. This is important because it indicates that no unknown, biologically active fumonisins were present in the extracts and that chemical analyisis of the extracts is adequate to estimate toxicity.

Technical Abstract: Cooking and steeping corn kernels in alkaline water (nixtamalization) extracts fumonisins, thereby reducing their concentration in masa and tortilla products. However, chemical analysis of fumonisins in commodities and foods could underestimate fumonisin toxicity if unknown, but biologically active fumonisins are present. To investigate this possibility, the biological activity of concentrated extracts of corn naturally contaminated with fumonisin B1 (FB1), masa made from the corn, and baked and fried tortilla chips made from the masa were determined in vitro. Vero cells (ATCC Cl-81) were grown in 1 ml wells and exposed to 4 microliter of the redissolved extracts for 48 hr, at which time the total sphinganine (Sa) and sphingosine (So) in the corn and each product was determined by HPLC. The corn extract inhibited ceramide synthase as indicated by increased Sa (mean=132 pmole/well) and Sa/So ratios (Sa/So=2.24). In contrast, Sa and Sa/So in the wells exposed to the masa and tortilla chip extracts (mean Sa 14-24 pmole/well; mean Sa/So=0.17 to 0.28) were similar to those of control-treated exposed cells (Sa=9 pmole/well; Sa/So= 0.10). FB1 concentrations of the masa and chip extracts (4-7 microgram/g; determined by HPLC) were likewise reduced 80-90% compared to the corn extract (32 microgram/g). Together, the results indicate that nixtamalization removes fumonisins from corn, significantly reduces both the FB1 concentration and the biological activity in the masa and tortilla chips products, and provide no evidence for the presence of unknown ceramide synthase inhibitors in the corn, masa, or tortilla chips.