Enzymes have long been used as factors to increase nutrient digestibility and therefore the efficiency of animal production while reducing the environmental impact of the industry. What might be new for some is the fact that enzyme-producing microorganisms may be incorporated in animal feeds with a different objective, namely for the degradation of mycotoxins, scientifically referred to as biotransformation.
Although many animal producers will deny or underestimate the fact that mycotoxins exist in the cereals and in animal feeds, the truth is that they occur more often than not. At the present, the search for good quality mycotoxin-free feedstuffs has become an increasingly complicated task as global warming affects crops, as grain prices are affected by their scarcity and as by-products are commonly being used as alternative ingredients. Mycotoxins in the 2009 US corn had a great impact worldwide. This year, Australia is struggling with mycotoxin contamination in wheat after a very wet December and January. Still to be known are the effects of Japan's tsunami in the country's crops. These are just three out of numerous examples of a single fact: mycotoxins are here to stay, so we better think about how to manage them.
With obvious differences depending on the country, mycotoxin binders are nowadays much more acknowledged and frequently used as part of feed formulations. The objective of a toxin binder in an animal diet is therefore to adsorb mycotoxins thus reducing their bioavailability for the organism or, in other words to avoid their absorption by the animal. Binders are important control agents in the case of adsorbable mycotoxins, such as aflatoxins.
What to do in the case of other widespread mycotoxins such as zearalenone, vomitoxin, T-2 toxin, fumonisins and ochratoxin A? For those, it is widely known that adsorption by binders is not an efficacious solution and often, the use of certain adsorptive materials may lead to greater problems due to the unspecific binding of essential nutrients. This is why biotransforming agents are important. Biotransformation stands for the conversion of mycotoxins into less toxic molecules by enzymes or microorganisms. This degradation takes place in the gastro-intestinal tract of the animal consuming mycotoxin-contaminated feed. Initial research in the field of mycotoxin biotransformation goes back 40 years; however, so far few microorganisms have shown the capacity of degrading mycotoxins and of those, fewer can be used safely and in a stable way as animal feed additives.
For the elimination of the toxic effects of trichothecenes a large family of more than 200 structurally similar mycotoxins, from which vomitoxin (deoxynivalenol or DON) and T-2 toxin are the most well known members Eubacterium BBSH 797 was developed and patented by Biomin. Enzymes (for example, epoxidases) play an important role by enabling the specific disruption of the toxic epoxy ring possessed by this group of mycotoxins (Figure 1).
Some years later, the non-pathogenic yeast, T. mycotoxinivorans MTV was isolated, described and patented for its ability of degrading zearalenone and ochratoxin A. For the elimination of zearalenone's negative effects, it is vital that the lactone ring within the molecule is destroyed. This reaction is once again mediated by enzymes (e.g. esterases; Figure 2). While doing so, zearalenone resemblance with the sexual female hormone estradiol is lost and therefore the impairment of the reproduction system is avoided. In the case of ochratoxin A, cleavage of the phenylalanine moiety results in the derivate ochratoxin alpha (Figure 3), considerably less toxic than the original molecule.
The production of the enzymes that mediate these reactions occurs within the gastrointestinal tract of the animal and therefore their production and activity cannot be quantified as in the case of purified enzymes. For this reason and to enable the use of these microbes as feed additives, the fermentation and stabilisation processes have been optimised with respect to their fast growth and high biotransformation activity of the resulting product. For enhancement of stability during storage and within the gastrointestinal tract, encapsulation processes were implemented. All in all, their activity is not simple: not only need they to show a rapid degradation of the mycotoxin into less or non-toxic metabolites, but also to keep their activity at different pH values and complex environments with the presence of metabolites and nutrients. Their non-toxicity must be assured and the possibility of being applied as lyophilisates should be granted for a practical use in animal diets.
In summary, a proper risk management tool allows the elimination of mycotoxins by adsorptive materials, commonly known as binders, and, most importantly, allows the conversion of their toxic structures into non-toxic, harmless metabolites, by biotransformation facilitated by enzyme-producing microorganisms.
August 2011
