General References

H. Cabezas, Jr., M. B. Kabiri, and D. C. Szlag, "Statistical Thermodynamics of Phase Separation and Ion Partitioning in Aqueous Two-Phase Systems," Bioseparation 1, 227-233 (1990).

M. Certel and M. E. Ertugay, "The Thermodynamics of Water Activity in Foods," Gida 21, 193-199 (1996).

A. Cesaro, "The Role of Conformation on the Thermodynamics and Rheology of Aqueous Solutions of Carbohydrate Polymers," J. Food Eng. 22, 27-42 (1994).

G. Grasso, "Modellistic Description of Food Materials and Their Technologies, II: The Macrostructural Approach," Industrie Al-imentari 35, 923-932 (1996).

C. Kapseu et al., "Thermodynamics of Solid Formation in Cottonseed Oil," J. American Oil Chemists' Society 68, 237-240 (1991).

H. Kumagai et al., "Application of Solution Thermodynamics to the Water Sorption Isotherms of Food Materials," Bioscience Biotechnol. andBiochem. 58, 475-481 (1994).

H. Kumugai, A. Mizuno, and T. Yano, "Analysis of Water Sorption Isotherms of Superabsorbent Polymers by Solution Thermodynamics," Bioscience Biotechnol. and Biochem. 61, 936-941 (1997).

M. Rutgers, K D. Van, and H. V. Westerhoff, "Control and Thermodynamics of Microbial Growth Rational Tools for Bioengineering," CRC Critical Rev. in Biotechnol. 11, 367-395 (1991).

V. A. Taran, O. G. Fedorov, and A. I. Pokatilov, "Mathematical Formulae for Determining the Dessication Thermodynamics of Chilled Foods by Means of Energy Entropy," Kholodil'naya Tekhnika 12, 21-24 (1988).

George M. Pigott University of Washington Seattle, Washington


In addition to the many well-known major components (protein, fat, carbohydrate, and fiber) and trace nutrients (vitamins, minerals, and nonessential compounds), our food contains thousands of naturally present toxic compounds. Although these chemicals are in every meal we eat and are present in much greater quantities than residues of synthetic chemicals such as PCBs and pesticides, they have traditionally received relatively little attention compared to these well-known human-made chemicals. Furthermore, the mechanisms of action of natural toxins— metabolic activation, interaction with critical cellular macromolecules—are no different from those of synthetic toxins. In short, our bodies handle toxins similarly regardless of their origin. Many of the toxins presented here are known to cause or strongly suspected of causing cancer in laboratory animals and are therefore potentially carcinogenic in people. The human health risk posed by individual natural toxins varies considerably due to a variety of factors such as dose, inherent potency, variety of the diet, and presence of detoxifying factors. In any event, natural toxins pose a far greater health risk than do synthetic chemicals in our foods, despite the popular notion that "natural is good."

An issue of major concern is the relationship between diet and various human diseases, including cancer. As the single most important cancer variable to be identified from epidemiology studies, diet contributes to approximately 35% of the variation in cancer rates among individuals and populations in the United States. Other factors such as food additives, genetic predisposition, industrial pollution, and pesticide contamination play comparatively minor roles in human cancer rates. Excluding smoking, diet-related factors account for over 50% of all remaining cancer deaths in this country, or 150,000 food-related cancer deaths per year in the United States alone.

Natural toxicants are defined here as naturally occurring substances in plants or other food products that exert undesirable or unhealthy effects when they are consumed. Although not intended to be an exhaustive, all-inclusive discussion of natural toxins, this section will center on those that are particularly well studied and characterized or are of contemporary interest in food toxicology. The focus of this chapter will be not on bacterial toxins, but on three major categories of food toxicants: (1) toxins from plant or plant-derived foods, (2) mold-produced toxins (or mycotox-ins), and (3) toxic substances created during cooking or other processing of the food (or induced toxins). An additional yet important category of induced toxicants is endogenous toxic substances that may appear inadvertently in genetically manipulated plant materials that result from efforts to alter plant quality. This latter category will also not be considered here.

Our food also contains natural chemicals that can counteract and thereby prevent the adverse effects of many natural and synthetic toxins. Though much more work on these chemopreventives is needed, the data suggesting that some plant foods can actually reduce the incidence of certain types of cancer thus far are very encouraging. Hundreds of animal and epidemiological studies have identi fied several foods or specific compounds that offer protection against the carcinogenic effects of a wide variety of natural and synthetic chemicals. A few compounds have been shown to actually reverse the carcinogenic process in animals. As might be imagined, the field of chemopreven-tion is one of the most exciting areas in nutritional toxicology and cancer research. The reader is encouraged to consult a review on food chemopreventives.

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