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4 Food Safety Assessment Methods in the Laboratory: Toxicological Testing Methods
Over the years, many tests have been devised to determine the adverse effects of chemicals in living organisms. Procedures are available for use with intact animals, laboratory-cultured single-cell organisms, isolated organs (perfused liver or lungs), or mammalian cell lines. Toxic endpoints used by investigators range from the traditional acute lethality, weight loss, and carcinogenesis to exciting new tests for effects of immunosuppression, behavioral aberrations, and genetic injury. Given this spectrum of procedures, an orderly and systematic approach to toxicity testing is undeniably needed. One of the first proposals in the U.S. for a systematic strategy involved the safety decision tree approach of the Food Safety Council Scientific Committee in 1980. In 1982, the publication titled Toxicological Principles for the Safety Assessment of Direct Food Additives and Color Additives used in Foods (also known as Redbook I) was developed by the U.S. Food and Drug Administration, Bureau of Foods (now the Center for Food Safety and Applied Nutrition, CFSAN). The draft for Redbook II was available in March 1993, followed by Redbook 2000: Toxicological Principles for the Safety of Food Ingredients, which is available electronically at http://vm.cfsan.fda.gov/~redbook/red-toct.html.
The overall strategy for assessing food additives has received strong endorsements from the scientific community, and only the details have been modified to keep pace with scientific advancements. Figure 4.1 gives a schematic representation of the safety decision tree protocol proposed by the U.S. Food Safety Council. The first step involves the careful selection and characterization of the substance to be tested. Preliminary evaluations of the substance are made by assessing physical and chemical properties of the test substance. A literature search is done to collect any available information regarding the toxicity testing of the substance. Exposure assessment involves gathering information on probable human exposure, i.e., estimated intake levels for the population as a whole or any subpopulation that might be vulnerable to significant levels of the substance. An example of a subpopulation is diabetic patients when the test substance is a new sugar substitute.
Defined test material
Testing begins with acute toxicity studies, starting with a single dose administered to a rodent species. Acute toxicity studies provide background information and guidance for subsequent tests to be used in the assessment. Unless the substance is found at this point to be too toxic for further study, the assessment moves further to gather information on genetic toxicology and toxicokinetics of the substance. Negative genetic toxicity results lead to metabolism, subchronic, and chronic toxicity testing.
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