|Shier, W. Thomas|
Submitted to: Journal of Toxicology Toxins Reviews
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2003
Publication Date: 10/1/2003
Citation: Shier, W., Abbas, H.K., Abou-Karam, M., Badria, F.A., Resch, P.A. 2003. Fumonisins: abiogenic conversions of an environmental tumor promotor and common food contaminant. Journal of Toxicology Toxins Reviews. 22:591-616. Interpretive Summary: Fumonisins are widespread contaminants of corn and manufactured corn-derived food products, which are produced by a fungus that is a ubiquitous contaminant of corn. Fumonisins are a food safety concern due to their ability to promote cancer and to cause birth defects. Numerous studies have shown that heat during cooking results in an apparent loss of fumonisins from corn-derived food products. The fumonisins were widely assumed to have been destroyed by the heat during cooking. In the present study radioactive fumonisin has been used in laboratory models of corn flake and tortilla chip manufacture, because it makes it easy to follow where the fumonisin is going during cooking. It was observed that the major fate of fumonisin caused by the dry heat of roasting, as is used in the manufacture of corn flakes, was for the toxin to become bound to many, if not all, of the proteins found in the corn. Corn is known to be up to 11% protein. The toxicity of protein-bound fumonisin has not yet been determined, but studies on the way the toxin is bound to protein raise concern that fumonisin may get released in a toxic form when the protein is digested after the corn flakes have been eaten. Frying tortilla chips resulted in reaction of fumonisin with fat degradation products and efficient extraction of the altered toxins out of the chips into the cooking oil. This observation suggests a strategy for removing fumonisins from fried foods without altering the taste and texture properties of the food. However, in conventional tortilla chip-manufacturing practice anything extracted into the hot cooking oil will get absorbed later by other chips. Understanding the food safety risk factors from fumonisin requires knowledge of the metabolites, particularly as they are formed during cooking.
Technical Abstract: Fumonisins are a series of sphingosine-analog mycotoxins produced by Fusarium verticillioides, a ubiquitous contaminant of stored corn (maize) world-wide. Extensive alterations in the structures of fumonisins are possible without loss of biological activity. Numerous laboratories have reported that fumonisin B1 (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 formed from the fat by non-oxidative thermal degradation of cooking oil. The N-fatty acylated fumonisin derivatives were efficiently extracted from the chips into the hot oil.