Critical control points for proper mycotoxin management by Dr. Ir. Anouck Witters, Impextraco NV

2.       Risk factors for mycotoxin contamination

The risk level for mycotoxins depends on climate conditions (temperature, humidity) since mold growth is favoured in hot and humid climates. Therefore, field as well as storage conditions need to be managed in order to minimize the risk for mycotoxin contamination. Nevertheless, equal field and storage conditions may face different mycotoxin problems according to the type of crops on the field. Including DDGS as a protein source in the feed, for example, implements an increased risk for mycotoxins (figure 1).

3.       Detection of mycotoxins

The increased detection of mycotoxin contamination is not only due to an increased prevalence of mycotoxins, but also because of improved analytical methods to detect them. The first and most crucial step in mycotoxin analysis is sampling of raw materials or feed. Samples should be representative for the whole batch, which means that the sample should be taken at random but equally divided spots of the batch. Indeed, mycotoxin contamination can be concentrated to so-called ‘hot spots’, while other parts of the batch are not contaminated at all. On the other hand, the quantity of the sample should be proportional to the total batch weight.

Another detection-issue is the presence of so-called ‘masked’ mycotoxins. These toxins are bound to a more polar molecule, like glucose, resulting in conjugated mycotoxins. These conjugates have been shown to escape the routine mycotoxin detection methods; however, the toxic precursors will be released by hydrolysis during digestion. Literature reports occurrences of DON- and ZEA-glucoside up to respectively 12% of DON and 20% of ZEA levels (figure 2) (Schneweis et al., 2002; Berthiller et al., 2005). So, analyzing samples only for mycotoxins and not for their glucoside-conjugates, will probably underestimate the real risk for contamination.

4.       Prevention and control of mycotoxins

If favourable growth conditions for fungi are met, it is very difficult to avoid the production of mycotoxins. However, effective prevention strategies will certainly limit the incidence of mycotoxins. Prevention can be implemented before harvest with a good management of the crop, harvesting and storage. It must be noted, however, that prevention does not remove present mycotoxins.

Many methods, chemical as well as physical, have been tested to remove mycotoxins from commodities. The problem is that they are costly, usually generate high losses and may reduce the palatability and the nutritional value of the raw materials. In practice, mycotoxin binders are most commonly used, whether or not combined with the strategy of biotransformation.

4.1 Use of mycotoxin binders

Binding mycotoxins is a widespread approach to reduce the toxin’s bioavailability in the gastrointestinal tract. One of the first scientific studies on binding properties of clays showed that a specific type of phyllosilicate clays, hydrated sodium calcium aluminosilicates (HSCAS), have high affinity for aflatoxin B1 (Phillips et al., 1988). Indeed, the good stability of the aflatoxin-HSCAS complexes over a wide pH range (2-10) and up to 37°C supports the in vivo efficacy of such binders (Sarr et al., 1990). Further studies have demonstrated that HSCAS can be very helpful to prevent aflatoxicosis in different species such as chickens, turkeys, goats, cows, pigs, or lambs. However, the efficacy of HSCAS seems to differ according to the type of mycotoxins: HSCAS are effective against aflatoxin B1 and ochratoxin A, while they appear totally ineffective to tackle trichothecenes (e.g. T-2 toxin, deoxynivalenol).

Although activated carbon has proven to be effective on binding mycotoxins in vitro, e.g. fumonisin B1 (Solfrizzo et al., 2001) or ochratoxin A, it did not show clear positive effects in vivo. Probably, this could be due to the fact that activated carbon can indiscriminately bind other dietary components, such as vitamins, minerals and drugs.

Stanley et al. (1993) reported Saccharomyces cerevisiae being helpful in the case of aflatoxin contamination; they concluded that the yeast cell wall binds mycotoxins.  The effects of yeast cell walls against ochratoxin were studied by Santin et al. (2003) in broilers. Their results indicate that zootechnical parameters, impaired due to ochratoxins, were not improved by application of yeast cell walls. Yiannikouris et al. (2004) investigated the interaction of yeast cell walls with zearalenone in vitro. They concluded that the chemical interactions are better described as adsorption rather than binding.

Based on literature, the main limitations of “mycotoxin binders” can be summarized as following:

• Their efficacy is limited to a few mycotoxins.

Generally speaking, binders are effective against so-called polar mycotoxins, such as aflatoxins. Indeed, these mycotoxins have a chemical structure which allows efficient binding. In the case of other mycotoxins, such as trichothecenes, binding efficacy is generally very poor, if not zero.

• Their in vitro efficacy does not guarantee their performance in vivo.

In vitro tests do not always represent what happens in the digestive tract as they are performed under specific and rather simple conditions. Not taking into account variable physiological parameters (pH variation, interaction with feed or enzymatic secretions) increases the risk to draw false conclusions. Indeed, mycotoxins may be released from the binder in the intestinal environment, as it is a reversible process.

• Some of them are not specific to mycotoxins.

Some binders interact with other dietary components, such as vitamins, minerals and drugs. This will limit the efficacy against the mycotoxin(s) and also affect the performance of the animals.

4.2 Biotransformation of mycotoxins

Due to the above listed drawbacks of mycotoxin binders, alternative strategies are recommended.  By means of live micro-organisms or enzymatic preparations, mycotoxins are biotranfsformed into non-toxic metaboliltes.

An Agrobacterium-Rhizobium was reported to be able to transform deoxynivalenol into a less toxic compound, 3-keto-deoxynivalenol (Shima et al., 1997). This biotransformation was suggested to be caused by an extracellular enzyme excreted by the organism. A similar transformation of trichothecenes was observed by Völkl et al. (2004).

Zearalenone, which interferes with oestrogen receptors, can be converted into a far less oestrogenic-like product, 1-(3,5-dihydroxyphenyl)-10’-hydroxy-1’-undecen-6’-one (Takahashi-Ando et al., 2002). The enzyme responsible for the detoxification appears to be a hydrolase that cleaves the lactone ring.

The application of such enzymatic transformations in the feed sector offers new opportunities. Indeed, compared to binders, enzymes can have a higher specificity and perform a non-reversible reaction. Moreover, the enzyme activity is not limited to polar mycotoxins only.

Fig. 3 Gut simulator model developed by HAS Den Bosch research group (the Netherlands). This model was used by Impextraco (Belgium) to develop their feed additive against mycotoxins, Elitox®.

In the development of a solution to counteract the effects of mycotoxins in feed, Impextraco (Belgium) screened many products, including binders and enzymes, by means of this gut simulator model. The best toxin binder that emerged from this screening was combined with enzymes. In addition, a biopolymer was selected for its mycotoxin binding properties. Moreover, the biopolymer has been proven to be antibacterial and antifungal. The included natural extracts and vitamins act against the symptoms associated with mycotoxin contamination. In conclusion, Impextraco’s product (Elitox®) unites in one single product different strategies to counteract a wide range of mycotoxins.