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SCIENCE
A technique used to assess the allergenicity of novel proteins in food could be misleading. The method, which correlates a protein's allergenic potential with resistance to simulated digestion, is one measure used in evaluating the safety of food derived from genetically engineered crops (C&EN, Jan. 7, page 20). The test is based on the assumption that the less a food protein is digested, the more likely it is to cause an allergic reaction. But that is not necessarily the case, according to Tong-Jen Fu, Upasana R. Abbott, and Catherine Hatzos of the National Center for Food Safety & Technology, a research consortium in Chicago [J. Agric. Food Chem., 50, 7154 (2002)]. In fact, "we could not find a clear-cut distinction between the digestibility of food allergens and nonallergens," says Fu, a research chemical engineer with FDA.
Unfortunately, the assay is being misused, says Steve L. Taylor, who was a member of the decision tree task force and is codirector of the Food Allergy Research & Resource Program at the University of Nebraska, Lincoln. "Over the years, many scientists and regulators have placed too much emphasis on digestive stability as a criterion. It is one of several criteria that should be examined in allergenicity assessment," he says. Taylor, who heads his university's food science and technology department, thinks it would be useful to do a thorough study of the impact of the ratio of protein to pepsin--the enzyme used in the assay to digest the protein--on the digestibility results. In fact, he believes that differences in this ratio may partly explain the discrepancy between Fu's findings and those of other researchers such as James D. Astwood, director of Monsanto's Product Safety Center. Taylor also disagrees in some cases with Fu's characterization of the proteins she tested as allergens or nonallergens. Although Fu's work casts doubt on the validity of the protein digestion assay as currently designed, the test may still have utility. "Some people believe that a protein that resists digestion retains sufficient structural integrity to stimulate immune reactions," she says. "The in vitro digestion assay provides a good estimate of this protein integrity." However, different labs have been using different conditions to measure digestibility and as a result are obtaining different perceived results in allergenicity. So Fu says assay conditions need to be standardized. HESI recently sponsored a project to do so and plans to publish its results. Fu's data indicate that more resources should be devoted to characterizing additional allergenicity measures, Holsapple adds. These include blood tests, work with animal models, and homology comparisons, in which the amino acid sequence of a test protein is compared with that of known allergens. In sum, he says, "no one parameter can be used to assess the allergenic potential of a novel protein."
"Over the years, many scientists and regulators have placed too much emphasis on digestive stability as a criterion. It is one of several criteria that should be examined in allergenicity assessment." Steve L. Taylor, University of Nebraska, Lincoln
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