Detoxification aflatoxins

Chemical detoxification processes or decontamination will include degradation, destmction and/or inactivation of the mycotoxin. In any such process the reduction of the mycotoxin to safe levels should not result in toxic degradation products or reduce the palatability or nutritional properties of the commodities. Aflatoxin has been the subject of most studies and only a relatively small number of these offers any hope of success. There is as yet no FDA or EC fully approved method for aflatoxin detoxification in human foods. Current methods in advanced stages of approval use ammonia in the gaseous form or as an ammonium hydroxide solution at various temperatures, pressure, moisture contents and reaction time to degrade aflatoxins in various animal feedstuffs. There have been extensive studies using two processes, viz ... 

Although physical and chemical methods of detoxification are not the subject matter of the present review, some recent works have been included to have a latest insight into the mechanism of aflatoxin detoxification. Some of the conventional methods have already been mentioned elsewhere [19]. 

Effect of growth subatratea, age of culture, and aeration on aflatoxin detoxification... 

The exceptional reactivity of aflatoxin B1 exo-8,9-epoxide raises the question of its potential detoxification by EHs. Despite the short half-life, the epoxide does react with DNA (toxification) and glutathione 5-transferases (detoxification), but a role for EH appeared dubious [207], Rat liver or recombinant rat EH has since been shown to provide a modest enhancement of up to 22% in the hydrolysis rate of aflatoxin B1 exo-S,9-epoxide, and to decrease somewhat the genotoxicity of aflatoxin B1 when the ratio of EH to cytochrome P450 is high (ca. 50-fold). Purified human EH provided no such enhancement in hydrolysis, nor did it have a clear effect on genotoxicity. Thus, little evidence exists to support a role for EH in the detoxification of aflatoxin B1 [208],... 

A specific example involving aflatoxins is shown in Box 6.8. We shall see other examples of glutathione reacting as a nucleophile in detoxification reactions, where conjugation is not the result of nucleophilic substitution. For example, it might be nucleophilic addition to an electrophile such as an unsaturated carbonyl compound (see Box 10.20). 

Simula, T.P, Glancey, M.J. Wolf, C.R. (1993) Human glutathione S -transferase-expressing Salmonella typhimurium tester strains to study the activation/detoxification of mutagenic compounds studies with halogenated compounds, aromatic amines and aflatoxin Bp Carcinogenesis, 14, 1371-1376... 

TD Philips, BA Clement, D Park. Approaches to reduction and detoxification of aflatoxins in foods and feeds. In DL Eaton, JD Groopman, eds. The Toxicology of Aflatoxins Human Health, Veterinary and Agricultural Significance. New York Academic Press, 1994, pp 383-389. 

Finally, biological detoxification or biotransformation, or degradation of mycotoxins, especially aflatoxin by microbial systems to a metabolite(s) that is... 

Figure 13.7. Glutathione conjugation to reactive metabolites by GSTs. Ultimate carcinogens such as benzo[a]pyrene 7,8-diol 9,10-epoxide and aflatoxin B1 8,9-epoxide are glutathione-conjugated for detoxification by GSTM1, GSTp, and GST A, respectively. Lipid peroxidation product 4-hydroxy-2-nonenal is preferentially detoxified by GSTA.

Heathcote JG, Hibbert JR Biochemical effects, structure activity relationships in Goldblatt LA (ed) Aflatoxin Chemical and Biological Aspects. Amsterdam, Elsevier, 1978, pp 112-130. Dickens JW Aflatoxin control programme for peanuts. J Am Oil Chem Soc 1977 54 225A-228A. Goldblatt LA, Dollear FG Review of prevention, elimination and detoxification of aflatoxins. Pure Appl Chem 1977 49 1759-1764. 

FIGURE 10.65 Conversion of aflatoxin Bj to the epoxide form and pathways for detoxification of the epoxide. 

The ammoniation of aflatoxin B i) was studied as a means of possible detoxification of contaminated foodstuffs. Aflatoxin Dj (22) arises through a mechanism whereby the coumarin lactone undergoes ammonolysis with ammonium hydroxide. The resulting ammonium salt is then postulated to decompose to the carboxylic acid, which decarboxylates by virtue of the 0-keto group at C-3, thereby giving the desired structure (22)89,90). 

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