Fumonisins: Abiogenic conversions of an environmental tumor promoter and common food contaminant

Fumonisins are a series of sphingosine-analog mycotoxins produced by Fusarium verticilhoides, a ubiquitous contaminant of stored corn (maize) world-wide. Extensive alterations in the structures of fumonisins are possible without complete loss of in vitro toxicity. Numerous laboratories have reported that fumonisin B-1 (FB1) levels in corn-derived foods are reduced during roasting and frying. We have conducted radiotracer studies to determine the fate of tritium-labeled FB1 added in laboratory models of corn flake manufacture (roasting), and tortilla chip manufacture (frying). These studies have confirmed that most, but not all, FB1 is converted to other substances during cooking. Under roasting conditions the major conversion pathway resulted in radiolabeled FB1 becoming covalently bound to proteins. Several lines of evidence supported a proposed role for FB1-anhydride, an intermediate formed by loss of water from a FB1 side chain, which enabled the toxin to bind covalently to proteins by reacting with amino groups. Under nixtamalization/frying conditions in preheated cooking oil, both FB1 and hydrolyzed FB1 were efficiently N-fatty acylated to the corresponding ceramide derivatives, presumably by fatty acid anhydrides or other degradation products formed from the fat by non-oxidative thermal degradation. The N-fatty acylated fumonisin derivatives were efficiently extracted from the chips into the hot oil. We will not understand the full threat to food safety posed by the fumonisins until we know what they are converted to during cooking, and what is the toxicity of those conversion products.