Chemical Treatments for Mycotoxin Decontamination of Raw Materials

Several strategies are available for the detoxification or decontamination of commodities containing mycotoxins. These can be classified as chemical, microbiological or physical. It should be noted that chemical treatment is not allowed within the EC for commodities destined for human food. Many studies have evaluated the use of chemicals for the detoxification and decontamination of contaminated raw materials by destroying or modifying mycotoxins so as to reduce or eliminate the toxic effect. The chemicals used fall into the categories of acids, bases (e.g. ammonia, sodium hydroxide), oxidizing reagents (e.g. hydrogen peroxide, ozone), reducing agents (e.g. bisulfite, sugars), chlorinating agents (e.g. chlorine), salts and miscellaneous reagents such as formaldehyde. Often chemical treatments have been used in combination with physical treatments to increase the efficacy of decontamination.

This fact sheet will briefly review some aspects of chemical detoxification that can be used for important mycotoxins that can contaminate commodities.

Aflatoxins

A variety of chemicals (many acids, bases, aldehydes, bisulfite, oxidizing agents and various gases) can react to destroy (or degrade) aflatoxins effectively but most are impractical or potentially unsafe to use because of the formation of toxic residues or the effect on nutrient content, flavor, odor, color, texture, and/or functional properties of the product. Two techniques for detoxification of aflatoxins that have received considerable attention are ammoniation and reaction with sodium bisulfite. The ammoniation process using either ammonium hydroxide or gaseous ammonia has been shown to reduce aflatoxins (100-4000 microgrammes/kg) by up to 99% in corn, peanut meal-cakes, whole cottonseed and cottonseed products. If the reaction is allowed to proceed to completion, the process is irreversible (5). A high pressure/high temperature ammoniation process (80-120 Deg C/35-50 psi) for 20-60 min is used to remove aflatoxin from cottonseed and from cottonseed meal. The efficacy of ammoniation treatment to significantly reduce the toxicity (hepatic neoplasia, immunotoxicity) of aflatoxins has been demonstrated by feeding animals with ammonia-treated and untreated aflatoxin-contaminated corn, peanut meal and mixed feed. In the United States, the States of Arizona, Texas and California permit the ammoniation of cottonseed products and Texas, North Carolina, Georgia and Alabama have approved the ammoniation procedure for aflatoxin-contaminated corn. Mexico has approved ammoniation for corn and France, South Africa, Senegal and Brazil use this procedure to lower aflatoxin contamination levels.

It must be pointed out that ammoniated feed should not be fed to lactiferous cattle and sheep since the levels of residual aflatoxin B₁ in these products can still be higher than the maximum level permitted in Europe (e.g. 5 microgrammes/kg).

The fate of aflatoxin B₁ during small (SOCOFAG, NRI, IFF) and large scale (SOCOFAG, SKS, IFF) ammoniation processes has been recently studied in a EU-funded project and this confirmed the results of other studies in that more than 99% of aflatoxin B₁ was degraded. In particular, a reduction of aflatoxin B₁ from 2500 microgrammesg/kg to 15 microgrammesg/kg was observed in ammoniated peanut meal. However, the mutagenicity of ammoniated peanut meal extract was not completely eliminated, and this could not be explained by the low level of residual aflatoxin B₁. Degradation products of aflatoxin B₁ were isolated and tested for their toxicity, but not identified (1,2).

Sodium bisulfite (a common food additive) has been shown to react with aflatoxins (B₁, G₁, M₁ and aflatoxicol) to form sulfonate derivatives while peroxide and heat enhance the destruction of aflatoxin B₁ by sodium bisulfite added to contaminated dried figs. The practical application of this method has not yet been recommended since more studies are required in order to assess the biological activity of aflatoxin-sulfonate derivatives.

Treatment of corn with lime water in the manufacture of tortillas (nixtamalization) considerably reduces levels of aflatoxins although aflatoxins G₁ and G₂ are more susceptible to degradation than aflatoxins B₁ and B₂. However aflatoxin is produced again by acidification so that the corn is not truly detoxified.

Ochratoxin A

Removal of ochratoxin A from feed grains has received limited attention and few studies have been performed to chemically destroy this mycotoxin. Studies show that formic, propionic and sorbic acids degrade ochratoxin A at concentrations ranging from 0.25% to 1% after exposure of 3-24 hours. Ammoniation almost completely decomposes ochratoxin A in corn, wheat and barley, while heating with 0.5% sodium hydroxide or autoclaving were nearly as effective treatments (7). Destruction of ochratoxin A has been observed after treatment with sodium hypochlorite.

Fumonisins

Treatment of fumonisin B₁-contaminated corn (100 mg/kg) simulating modified nixtamalization (heat treatment with NaHCO3 + H2O2 alone or with Ca(OH)2) gave 100% reduction of fumonisin B₁ whereas the traditional nixtamalization (treatment with Ca(OH)2 only) was not effective because it produces hydrolyzed fumonisin B₁ which is still toxic (6).

The heating of an aqueous solution of fumonisin B₁ (180 mg/l) with reducing sugars such as d-fructose results in the formation of N-(carboxymethyl) fumonisin B₁ that is less toxic than fumonisin B₁ (3).

Ammoniation of Fusarium verticillioides (the fumonisin producing fungus) culture material as well as naturally contaminated corn, for 4 days at 50 Deg C and atmospheric pressure, resulted in the reduction of fumonisin B₁ by 30 - 45% though the toxicity of the culture material in rats was not altered by that treatment (4).

Trichothecenes

Calcium hydroxide monomethylamine has been used to decontaminate feeds containing T-2 toxin and diacetoxyscirpenol at 10 to 20 mg/kg; the success of the procedure is dependent on the moisture content of the feed and the processing temperature. In particular, about 50% of mycotoxin reduction was observed when the treatment was performed at about 25 Deg C and 10% moisture in 4 hours; when the moisture content was increased to 25% T-2 toxin level was reduced by 95 to 99%.

Sodium bisulfite solutions were able to reduce deoxynivalenol (DON) level (85%) in contaminated corn (4.4 mg/kg DON) and form a DON-sulfonate conjugate when the treatment was performed at 80 Deg C for 18 hours (8). Because this compound appeared to be nontoxic to pigs, this treatment has been proposed for decontaminating DON-contaminated corn destined for use in pig feeds.

Other chemicals (hydrochloric acid, hydrogen peroxide, sodium hypochlorite, ascorbic acid and ammonium carbonate) did not prove to be as effective as sodium bisulfite and had little or no effect on DON level.

References

1.	Hoogenboom L.A.P., Tulliez J., Gautier J.-P., Coker R.D., Melcion J.-P., Nagler M.J., Polman Th. H.G. and Delort-Laval J., 2001a. Food Addit. Contam., 18, 47-58.
2.	Hoogenboom L.A.P., Polman Th. H.G., Neal G.E., Verma A., Guyomards C., Tulliez J., Gautier J.-P., Coker R.D., Nagler M.J., Heidenreich E. and Delort-Laval J., 2001a. Food Addit. Contam., 18, 329-341
3.	Howard P.C., Churchwell M.I., Couch L.H., Marques M.M. and Doerge D.R., 1998. J. Agric. Food Chem., 3546-3557.
4.	Norred W.P., Voss K.A., Bacon C.W. and Riley R.T., 1991. Food Chem. Toxicol., 29, 815-819.
5.	Park D.L., 1993. Food Addit. Contam., 10, 49-60.
6.	Park D.L., Lopez-Garcia R., Trullo-Preciado S. and Price R.L. In: Fumonisins in Food. L.S. Jackson, J.W. Devries and L. Bullerman (eds.), Plenum Press, New York, 1996, 335-344.
7.	Scott P.M., 1996. Food Addit. Contam., 13, 19-21.
8.	Young J.C., Trenholm H.L., Friend D.W. and Prelusky D.B.,1987. J. Agric. Food Chem., 35, 259-261.