Toxic phytochemicals

By necessity, herbivores have evolved GIT and systemic compensatory mechanisms that allow them to subsist on plant-based diets that have limited nutrient quality and include phytochemicals. Still, herbivores remain susceptible to some of the anti-nutrient and toxic phytochemicals. For example, several herbivores are sensitive to the phytotoxins associated with autumn crocus, which include colchicine (Yamada et al, 2000). As a consequence, herbivores tend to select species and portions of plants based on a combination of nutrient quality and concentrations of phytochemicals (Yeager et al, 1997), and this has an impact on habitat selection and plant ecology (Duncan and Gordon, 1999). Carnivorous species have not been under selective pressure to develop similar compensatory mechanisms, generally have only limited abilities to subsist on plant-based diets, and in many cases are less tolerant of phytochemicals. 

The point has been made in many of these chapters that methodological and scientific development over recent years is such that very considerable advances will be made over the next decade indeed, one suspects that such is the pace of advance that the information presented in this volume will before too long be considered dated. This is to be welcomed and, in our opinion, is greatly preferable to the former situation, in which texts on natural toxicants/phytochemicals/secondary metabolites often contained much the same general coverage over many years. 

Pradhan, S., Naik, S.N., Khan, M.A.I., Sahoo, P.K., 2012. Experimental assessment of toxic phytochemicals in Jatropha curcas oil, cake, bio-diesel and glycerol. J. Sci. Food Agric 92,511-519. 

Phytochemicals are biologically-active, non-nutritive secondary metabolites which provide plants with colour, flavour and natural toxicity to pests. The classification of this huge range of compounds is still a matter of debate, but they fall into three main groups ... 

The discovery that, in industrialised societies, diets deficient in fruits and vegetables can effectively double the risk of developing many different types of cancer has focused renewed attention on the beneficial properties of these foods (Block e/a/., 1992 Patterson ef a/., 1990 Southon and Faulks, 2002). As we have seen, plant foods are rich in micronutrients, but they also contain an immense variety of biologically active secondary metabolites providing colour, flavour and natural toxicity to pests and sometimes humans (Johnson et ah, 1994). The chemistry and classification of such substances is still a matter for much research and debate, but this has not prevented attempts to isolate and exploit substances that have variously been termed protective factors , phytoprotectants , phytochemicals and nutraceuticals . Phytochemical compounds include ... 

The different types or classes of phytochemicals can have multiple influences on the GIT (Kitts, 1994). For example, caffeine stimulates the motor, hormonal and secretory functions (Boekmaefa/., 1999). Although many phytochemicals reduce nutrient quality or availability, traditional herbal medicines have exploited some of these characteristics to improve health. Moreover, some of the systemic responses attributed to certain phytochemicals (beneficial or detrimental) can be explained by their influences on the GIT (Carbonaro et al., 2001). To date, the most of the information about phytochemicals is focused on the reductions in the functional capacities of the GIT (the bad), or the toxic properties (the ugly). There are also numerous examples of phytochemicals that can be used to obtain desirable GIT characteristics (the... 

Proteinaceous phytochemicals can contain toxic epitopes that elicit defense responses for example gliaden and glutein peptides which cause celiac disease and other mucosal disorders (Tighe and Ciclitira, 1995 Van de Wal et al, 1999). The mucosal inflammation caused by feeding carnivorous Atlantic salmon diets with soybean meal decreases rates of nutrient absorption (Nordrum et al, 2000), whereas the detrimental influence of such diets is much less pronounced when fed to omnivorous fish, such as catfish and tilapia. 

Phytate (myo-inositol hexaphosphate Fig. 15.3, structure 33) is found in many food species and can be considered as a phytochemical. Its role in the plant is primarily as a phosphate store in seeds, but it is found in other tissues as well, for example, tubers (Harland et al., 2004). Phytate and its hydrolysis products are anti-nutrients that chelate metal ions and thus reduce their bioavailability (Persson et al., 1998 House, 1999). This is particularly a problem with cereal grains, but pre-processing can improve mineral absorption from these foods (Agte and Joshi, 1997). There is some concern that high phytate foods could also contain higher levels of toxic heavy metals caused by natural accumulation. Plants also contain phytate-degrading enzymes that can also influence metal ion bioavailability (Viveros et al., 2000). 

Beier R C and Nigg H N (1992), Natural toxicants in foods , in Nigg H N and Seigler D, Phytochemical Resources for Medicine and Agriculture, Plenum Press, UK, 247-368. 

Manners, G. D. and Pfister, J. A. 1993. Normal phase liquid-chromatographic analysis of toxic norditerpenoid alkaloids. Phytochemical Analysis, 4 14-18. 

Although a toxic plant chemical may not fit either category perfectly, those chemicals discussed below that are tissue specific would generally be considered to show specific resistance. It Is interesting to note that those phytochemicals that are especially toxic to one group of Insects are quite often essential dietary Ingredients or feeding stimulants to other Insects that feed primarily on that plant. 

Dr. Bidlack is past president of the Food Safety Specialty Section of the Society of Toxicology, served on the International Life Sciences Institute Committee on Nutrition and Food Safety, and held the position of scientific advisor for the subcommittee on iron and health and the subcommittee on apoptosis related to fumonisin toxicity. He has also served as a member of the board for the Certification Board for Nutrition Specialists and actively contributed to the creation of the national certification exam. In addition, he is serving on the editorial board and as book editor for the Journal of the American College of Nutrition. He served as an editor of two books on phytochemicals published by Technomics and four others published by CRC Press the seventh in the series is in press. He continues to review grants for several agencies and universities. Currently, Dr. Bidlack is serving as a member of the board of the California Department of Food and Agriculture. 

Mattocks A. R. (1972) Toxicity and metabolism of Senecio alkaloids. In Phytochemical Ecology, ed. J. B. Harborne pp. 179-200. Academic Press, New York. 

The search for the exact sites of ion and compound deposition in plants and the nature of the chemical species involved has been carried out with a number of aims The elucidation of various mechanisms of phytochemical importance mineral uptake and utilisation toxicity and tolerance exhibited by many individual species and the study of plants that accumulate or hyperaccumulate metals. The literature for a number of individual elements to the late 1970s has been reviewed (Farago, 1981) and the phytochemistry of metal hyperaccumulators has been reviewed by Baker and Brooks (1989). 

Integrated bioprocesses can be used to enhance the production of valuable metabolites from plant cell cultures. The in situ removal of product during cell cultivation facilitates the rapid recovery of volatile and unstable phytochemicals, avoids problems of cell toxicity and end-product inhibition, and enhances product secretion. In situ extraction, in situ adsorption, the utilization of cyclodextrin, and the application of aqueous two-phase systems have been proposed for the integration of cell growth and product recovery in a bioreactor. The simultaneous combination of elicitation, immobilization, permeabilization, and in situ recovery can promote this method of plant cell culture as a feasible method to produce various natural products including proteins. 

Although the chemical constituents of plants of the genus Aconitum have been extensively studied, mainly due to the presence of toxic and bioactive alkaloids, there are only few works regarding the phytochemical composition of A. naviculare. 

Betz, J.M., Andrzejewski, D., Troy, A., Casey, R.E., Obermeyer, W.R., Page, S.W. and Woldemariam, T.Z. (1998) Gas chromatographic determination of toxic quinolizidine alkaloids in blue cohosh Caulophyllum thalictroides (L.) Michx. Phytochem. Anal. 9, 232-236. 

Genistein and daidzein directly affect testosterone metabolism, reducing the toxic metabolites of testosterone. Genistein, an isoflavone, also seems to slow or prevent the metastasis of invasive cancer cells. It is believed to work by preventing the formation of new blood vessels to cancerous tumors. Histoculture studies of genistein have shown that this phytochemical reduces the growth of prostatic cancer tissue. 

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