5. Use of polymers to prevent AFB1 toxic effects in poultry

As it was mentioned in Section 1, an important approach to prevent aflatoxicosis in livestock and poultry is the addition of non-nutritional adsorbents in the diet to bind AFB1 in the gastrointestinal tract, reducing its bioavailability, which leads to a reduction of mycotoxin uptake as well as distribution to the blood and the target organs. These adsorbents are large molecular weight compounds that are able to bind the mycotoxin, forming a stable complex adsorbent-mycotoxin, which can pass through the gastrointestinal tract of the animals without dissociating the AFB1, to be eliminated via the feces [22].

The efficacy of adsorption appears to depend on the chemical structure of both the adsorbent, the mycotoxin, and the feed components. The physicochemical properties of the adsorbents such as total charge, charge distribution, size of the pores on the surface, surface area, iodine number, methylene blue index, and pH take on an important function in binding effectively. On the other hand, the properties of the adsorbed mycotoxins, like polarity, solubility, size, shape, charge distribution, and dissociation constants, also play a significant role. It has also been mentioned that the high fiber content of the feed substrate increased the mycotoxin affinity to adsorbent [17, 18].

Even though clay minerals and aluminosilicate materials have been tested and recognized for their ability to bind AFB1 successfully [130, 131], the main risk of using them in animal feed is that they can also adsorb some feed vitamins and minerals, decreasing their utilization by animals [132, 133]. Another risk is that clays can release toxic components or elements bound to them, as heavy metals or dioxins, which can be released in the intestine of animals and accumulated in animal organs [134, 135].

Facing the problems of the use of clay and aluminosilicate adsorbents, other types of binders have been investigated in the search for new adsorbent materials such as organic binders or biopolymers and synthetic polymers [17, 112]. Both kind of polymers are large molecules that are composed of many monomers, whose large molecular mass relative to a small molecule produces unique physical properties playing important roles in our society [24]. Just a few synthetic polymers have been evaluated and demonstrated to bind mycotoxins in vitro and in vivo, such as cholestyramine, divinylbenzene-styrene, polyvinylpyrrolidone (PVP), and its modification polyvinylpolypyrrolidone (PVPP) [7, 17, 18, 112]; nevertheless, from these polymers, only PVP and PVPP have been tested against AFB1 in poultry. In vitro studies indicate that PVPP can bind up to 50 mg/kg of AFB1 from feed. On the other hand, in vivo studies carried out in broiler chickens demonstrated that PVPP could have ameliorated some serum biochemical and hematological parameters, it might have meliorated the detrimental effects of AFB1 on the immune system, and that the pathological changes were markedly inhibited by the administration of PVPP in the diet [136–139]. However, the cost of those polymers would be a limiting factor for practical applications.

Biopolymers are generally complex indigestible carbohydrates, non-toxic, biocompatible, and biodegradable, such as cellulose, cellulose, lignin, hemicellulose, glucomannans, peptidoglycans, and chitosan. They have been widely used as a promising biosorbents for the removal of various heavy metal ions and dyes [140], but recently cellulosic polymers and chitosan have been demonstrated to have ability to adsorb AFB1 [24, 141]. According to the in vitro results, both cellulosic polymers and chitosan were able to bind other important mycotoxins for poultry industry besides AFB1, which is a clear advantage over inorganic adsorbents since they are very effective in preventing aflatoxicosis, but their efficacy against mycotoxins such as zearalenone, ochratoxin, and trichothecenes is limited [17]. These biopolymers also pose multilayer porous structure filled with openings and channels that provide huge volume per sorbent surface unit, which is favorable in the adsorption process. Concerning to chitosan, different molecular weights, deacetylation degree, and cross-linked degree have to be tested for their AFB1 adsorption properties, because these characteristics might show different adsorptive capacity against this mycotoxin [24].

The results on the efficacy of polymers in sequestering mycotoxins are highly promising, although this field is still in its infancy and further research is needed. Furthermore, in vivo studies are needed to confirm the effectiveness of these materials against AFB1 toxic effects, since results in the past have indicated that there is great variability in the efficacy of adsorbing materials in vivo, even though the compounds may show potential adsorption capacity of the mycotoxin in vitro [22].
