15. Biological methods

The degree of adsorption capacities may vary (0–87%) among various mineral clay materials [95], and very few are actually used commercially. These considered as good absorbents include bentonites, zeolites and aluminosilicates. Studies have shown that sodium aluminosilicates, HSCAS (hydrated sodium calcium aluminosilicates) and sodium bentonites adsorb AFs [96] with adsorption potential of bentonites varying from 17 to 36%. A major advantage of these adsorbents is that they are relatively inexpensive and safe and can be easily incorporated in

Mineral adsorbents based on zeolites, silicates and phyllosilicates show different abilities to bind AFs. These possess active sites within interlayer channels at the basal planes on the surfaces or within pores, and at the edges of particles [98]. Bentonites are white, light weight and originate from volcanic ash comprising mainly of montmorillonite, the main constituent of bentonites. These are composed mostly of salts of Na, K, Ca of hydrated aluminosilicates and occasionally Fe, Mg, Zn, Ni, etc. but the composition varies from one deposit to another because of interchang-

or Na bentonites [86]. They have a layered microstructure, which allows AFs to bind at multiple sites including edges and basal surfaces especially at the interlayer region for adsorption [99, 100].

Zeolites possess strong colloidal properties to absorb water rapidly resulting in swelling and manifold increase in volume, giving rise to a thixotropic gelatinous substance [101, 102]. Hydration of the exchangeable cations creates a hydrophilic environment in the interlayer of montmorillonite, which influence the adsorption of different organic molecules, including mycotoxins on zeolite and montmorillonite particles [103]. The surfaces of zeolites derived HSCAS, attract polar functional groups of AFs, thus inhibit their absorption [93, 104] but is less effective against other mycotoxins. Zeolites selectively retain or release calcium during its passage through digestive system. Zeolites can absorb nitrogen of some amino acids and reduce the energy required for meat production. Zeolites suppress phosphorus utilization by forming indigestible compound with phosphorus through its aluminosilicate component [105]. Supplementation of HSCAS at the rate of 1.0% seems to diminish significantly, the adverse effects of AFs in young animals [93] as these have a high negative charge and are balanced by cations of such metals as magnesium, potassium and sodium located in the cavities, and therefore do not react with food/feed ingredients and act as inert material due to

Aluminosilicates are also used at a level up to 2% as "anti-caking" agents but a several disadvantages have been observed including the impairment of minerals utilization and having a narrow range of binding efficacy [93]. Bentonites minerals can influence Ca-metabolism and

AFB1 and T-2 toxin but not for zearalenone. Kececi et al. [107] determined decrease in calcium and phosphorus levels by AFs (2.5 mg/kg) for 21 days. Southern et al. [108] did not find any adverse effect on the growth and tibial mineral concentrations in chicks fed nutrient-deficient diets. Mineral clays reduce utilization of minerals including manganese, zinc, magnesium [109], chloride [95], copper and sodium [110]. Solís-Cruz et al. [111] conducted an in vitro study to evaluate the adsorption capacity of Chitosan (CHI), and three cellulosic polymers (Hydroxy propyl methyl cellulose, Sodium Carboxy methyl cellulose, and Microcrystalline Cellulose), on six mycotoxins (AFB1; FUB1; OTA; T-2; DON; and, ZEA) for poultry. All four cellulosic polymers

+

, Ca+2, and Mg+2. So they can be classified as Ca, Mg, K

. These are found to be effective for the adsorption of

, K+

animal feeds [97].

eable mono and divalent ions e.g. Na+

136 Mycotoxins - Impact and Management Strategies

their neutral pH or slightly alkaline nature [106].

bind nitrogenous cations such as NH4

Various bacterial, yeast and fungal species are able to degrade/remove mycotoxins and also can restrict fungal growth. This includes the use of Bacillus subtilis, NK-330 and NK-C-3 that effectively inhibit the fungus growth and AFs production [92]. The application of microorganisms e.g. Corynebacterium rubrum for bio-transformation of mycotoxins into less toxic metabolites is another option [9]. These micro-organisms act in intestinal tract of animals prior to absorption of mycotoxins but the concerned toxicity of products by enzymatic degradation and undesired effects of fermentation with non-native micro-organisms on food quality is yet to be investigated completely.

Saccharomyces cerevisiae and lactic acid bacteria (LAB) i.e. propionibacteria, bifidobacteria and lactobacillus rhamnosus strongly bind to their cell wall constituents mycotoxins without deleterious effects on animal health [9, 85, 93, 112]. Most yeast strains bind more than 15% (w/w) AFB1, which is highly strain specific by S. cerevisiae [112] and LAB for mycotoxins detoxification [113]. Generally, S. cerevisiae shows very low adhesion to the intestines [114], as opposed to LAB that show considerable adhesion to intestinal cells [115]. Coallier-Ascah and Idziak [116] and Thyagaraja and Hosono [117] found LAB to be inefficient binders of AFB1 due to the strains used, which may also depend on initial concentration of AFs [118]. Haskard et al. [119] showed that cell wall of L. rhamnosus has the ability to bind AFs predominantly to carbohydrates and to some extent, protein components that which is unaffected by pH of GI tract. The outer part of cell wall (26–32%) of S. cerevisiae contains a structure called glucomannan, which binds against mycotoxins [9]. The yeast cell wall comprises of 30–60% polysaccharides (β-glucan and mannan sugar polymers), 15–30% protein, 5–20% lipids and a small amount of chitin. Mainly, it contains 15–30% β-glucan and 15–30% MOS. Lahtinen et al. [120] found that peptidoglycans might be the most likely carbohydrate involved in the AFB1 binding process [121]. Kusumaningtyas et al. [122] used S. cerevisiae, Rhizopus oligosporus and their combination for detoxifying AFB1 in the chicken feed.

The supplementation of whole yeast and only yeast cell wall rather [53, 112, 123] have shown a reduction in mycotoxins toxicities, indicating possible stability of the yeast-mycotoxins complex along the gastrointestinal tract. The cell wall represents about 30% of total weight of yeast cell [112]. Glucomannan is a bi-layered structure that consists of a network of β-1,3 glucan with β-1,6 glucan side chains. This network is in turn attached to highly glycosylated mannoproteins. The proteins and glucans provide numerous easily accessible binding sites with different binding mechanisms such as Van Der Waals bonds, hydrogen bonding, ionic or hydrophobic interactions [93, 112, 124, 125]. Yeast glucomannan showed markedly high binding ability with AFs in vitro (75–90%) and in vivo [126, 127]. The carbohydrate fractions of cell wall may represent 90% of mannoproteins. MOS constitute approximately 50% of total carbohydrates [112]. The effect of 500 g of glucomannan is comparable with that of 8 Kg of clay for mycotoxins bindings [9].
