Mycotoxin binders achieve less than promised

Mycotoxin binders in the EU were added as a new functional group to the group of feed additives by amendment of (EC) No 386/2009 of 12 May 2009 on Regulation (EC) No 1831/2003. A mycotoxin binder (adsorbent/ denaturant) added to the diet should be able to interact in vivo with mycotoxins and restrict their absorption in the GI tract of animals.

Mycotoxin decomtamination in the EU

A number of approaches have already been used to counteract mycotoxins, though only a few have real practical application. With regard to mycotoxin decontamination, the European Commission is in favour of the use of physical decontamination processes and sorting procedures. However, neither the use of chemical decontamination processes, nor the mixing of batches with the aim of decreasing the level of contamination below the maximum tolerable level are legal within the European Union.

Mycotoxin binders: chemical sponge

Another way of trying to reduce the uptake of mycotoxins from contaminated feed is the use of mycotoxin binders. The aim of these additives is to inhibit the uptake of mycotoxins by an animal in vivo. The use of mycotoxin binding agents is occasionally recommended to farmers in order to protect animals against the harmful effects of mycotoxins occurring in contaminated feeds. These adsorbent materials are intended to act like a ‘chemical sponge’ and adsorb mycotoxins in the gastrointestinal tract, thus preventing the uptake and subsequent distribution to target organs.

What influences the efficacy of the adsorption

The efficacy of the adsorption appears to depend on the chemical structure of both the adsorbent and the mycotoxin. The most important feature for adsorption is the physical structure of the adsorbent, i.e. the total charge and charge distribution, the size of the pores and the accessible surface area. On the other hand, the properties of the adsorbed mycotoxins, like polarity,  solubility, shape and charge distribution, also play a significant role. Several studies have shown that a variety of adsorbent materials have high affinity for mycotoxins by the formation of stable linkages. Examples are activated carbon, hydrated sodium calcium aluminosilicates (HSCAS) and some polymers. Many adsorbents have been extensively studied and are promoted as animal feed additives. However, most of them appear to bind to only a small group of toxins while showing very little or no binding to others.

Aluminosilicates as adsorbents

Most studies related to the alleviation of mycotoxicosis by the use of adsorbents are focused on aluminosilicates, mainly zeolites, HSCAS, and aluminosilicate-containing clays, all consisting of aluminates, silicates and some interchangeable ions, mainly alkali metal and alkaline earth metal ions. Mineral clay products such as bentonites, zeolites, and aluminosilicates are the most common feed additives which are effective in binding/adsorbing aflatoxins.

The mechanism of mycotoxin binding has not been extensively studied. Regarding the applicability of aluminosilicates for the binding of mycotoxins, it can be concluded that available studies recognise their effect in preventing aflatoxicosis, but their efficacy against zearalenone, ochratoxin, and trichothecenes is limited. In addition to the narrow binding range concerning different mycotoxins, aluminosilicates have the disadvantage of adsorbing micronutrients and showing high inclusion rates for vitamins and minerals. There is also a risk of natural clays to be contaminated with dioxins.

Activated carbons as adsorbents

Activated carbon can efficiently adsorb most of the mycotoxins in aqueous solution, whereas different activated charcoals have less or even no effects against mycotoxicosis. However, activated carbons have shown their efficacy in in vivo studies for aflatoxins, ochratoxin A, diacetoxyscirpenol, and T-2 toxin and in experiments in vitro using a gastrointestinal model for deoxynivalenol, nivalenol, and zearalenone. Polymers, such as cholestyramine (an anion exchange resin) and polyvinylpyrrolidone (highly polar amphoteric polymer), have also been demonstrated to bind mycotoxins in vitro and in vivo, but these polymers are too expensive for practical use.

Biological solutions

A novel strategy to control mycotoxicoses in animals is the application of microorganisms capable of biotransforming certain mycotoxins into less toxic metabolites. Many species of bacteria and fungi have been shown to enzymatically degrade mycotoxins. Yeasts and lactic acid bacteria (LAB) occur as part of natural microbial population in spontaneous food fermentation and as starter cultures in the food and beverage industry. Saccharomyces cerevisiae and LAB, the two most important microorganisms in food fermentation, have been shown to bind different mycotoxins strongly to cell wall components.

Yeast or yeast cell walls show a potential as mycotoxin binders. Using only yeast cell walls instead of whole cells, the adsorption of mycotoxins can be enhanced. The cell walls harbouring polysaccharides (glucan, mannan), proteins, and lipids exhibit numerous different and easily accessible adsorption centres as well as different binding mechanisms, e.g. hydrogen bonds, ionic, or hydrophobic interactions. Various products which combine mycotoxin binding properties of different compounds have been developed to counteract the biological effects of cooccurring mycotoxins in animal feed. Due to their composition and the presence of different adsorbent materials, the products with multibinding capacity towards chemically different mycotoxins can be beneficial in reducing both individual and combined adverse effects of mycotoxins in animals.

Processing and binders

Physical processing of feed, such as pelleting, had a significant effect on the ability of a binding agent to reduce levels of AFM1 in milk when cattle was fed with AFB1 contaminated feed. It was also suggested that even though the ratio of AFB1 to binder in the contaminated feed could be an important variable to consider when using binders, it was not as important as the pelleting process.

In vitro studies do not always predict in vivo results. Adsorption in the animal is complicated by physiological variables and the composition of feed; factors which are rarely accounted for in the laboratory. Apart from that, animal studies are costly and not easy to perform. However, all potential mycotoxin binding agents must be tested in vivo to confirm their efficacy and safety and lack of interactions with nutrients.

Binder study

The aim of the JRC-study was to investigate the possible effect of mycotoxin binding agents (20 commercial products) on the analytical performance of standardised methods currently used for mycotoxin determination in feed. The study on the influence of the binders on the analytical results was performed for: AFB1, OTA, FUM B1 + B2, ZEA, DON, T2 + HT2 toxins. Naturally contaminated or spiked feed materials were applied for the investigation. Not sufficiently high naturally contaminated feed materials or materials with no corresponding mycotoxin found were spiked to obtain levels approximately 1.5 times higher than the legislative or recommended limits. This was the case for AFB1, DON and ZEA.

The great majority of binding agents, especially mineral adsorbents, are very effective in alleviating aflatoxicosis but their efficacy against other mycotoxins is limited. From this study it was concluded that the addition of the tested binders (at the level indicated by the manufacturer) did not result in lower analytical values for any mycotoxin currently regulated in feed. The combined effect of processing such as wet heating, pH-change, etc. in the presence of mycotoxin binders was not investigated, but might be a subject of interest for other studies.

Joint Research Centre Scientific and Technical Report, 2009. A. Kolossova, J. Stroka, A. Breidbach, K. Kroeger, M. Ambrosio, K. Bouten, F. Ulberth – Evaluation of the Effect of Mycotoxin Binders in Animal Feed on the Analytical Performance of Standardised Methods for the Determination of Mycotoxins in Feed. The study can be obtained for free from the JRC-website