Nutritionist > Dairy
Mycotoxin adsorbents and binders
As we know mycotoxins are usually found in combinations in complete animal feeds. A broad substrate binding capacity will ensure at least some fraction of all the mycotoxins will be rendered non-bioavailable and the bioavailable mycotoxins will be below the threshold of biological activity. Broad substrate binding capacity of a binding agent will also minimise the potential for toxicological synergy between mycotoxins.
Speciality feed additives, known as mycotoxin adsorbents or binding agents are the most common approach to prevent and treat mycotoxicosis in animals. It is believed that the agents bind to the mycotoxin preventing them from being absorbed. The mycotoxins and the binding agent are excreted in the manure.
The effective level of dietary inclusion for mycotoxin adsorbents will depend on the mycotoxin binding capacity of the adsorbent and the degree of contamination of the feed in question. A high binding capacity will minimise the level of inclusion and minimise the reduction in nutrient density caused by the feeding of the adsorbent. High levels of inclusion of adsorbents can also alter the physical properties of the feed which might impair feed processing such as pellet formation, in addition to altering the actual diet specification.
Mycotoxin binding is achieved through both:
-
Physical adsorption
- Relatively weak bonding involving van der Waals interactions and hydrogen bonding
-
Chemical Adsorption:
- (Chemisorption) is a stronger interaction which involves ionic or covalent bonding.
There are two types of mycotoxin adsorbent/binder:
- Inorganic binders
- Organic adsorbents
Inorganic mycotoxin binders are silica based polymers. Examples could include:
- zeolites
- bentonites
- bleaching clays from the refining of canola oil
- hydrated sodium calcium aluminosilicates (HSCAS)
- diatomaceous earth
- numerous clays
Phyllosilicates: bentonites/montmorillonites
- Phyllosilicates are characterised by alternating layers of tetrahedral silicon and octahedral aluminium coordinated with montmorillonite oxygen atoms
- Isomorphous substitution leads to a net negative charge which must be satisfied by the presence of inorganic cations (Na, Ca, Mg, K)
- Applications: Adsorbents for heavy metals, suspension-stabilising agents in coatings, bonding agents for foundry sands and washes, binder in pelletisation processes, desiccants in feed products.
- Tectoalumosilicates of alkali and alkaline earth cations that have an infinite three-dimensional cage-like structure
- Isomorphous substitution leads to a net negative charge which is satisfied by the presence of inorganic cations (Na, Ca, Mg, K)
- Applications: Adsorbents for ammonia, heavy metals, radioactive cesium and mycotoxins.
The amount of organic acids in clays is often very small and the inclusion rate of the clay products typically 2 kg/ton. Does the small amount of organic acid(s) really work in inhibiting moulds? The answer is NO; and it can actually do more harm than good: The small amount of acids quite often has no effect. Worst of all, if the acids do work, due to such small amounts, they are not enough to kill the mould. Instead, the acids change the pH of the environment and bring pH stress to the moulds. The pH stress can actually stimulates the moulds to produce MORE mycotoxins. (REMEMBER, mycotoxins are the secondary metabolites from moulds produced due to stress from environmental factors, such as pH)
Organic Adsorbents
Organic mycotoxin adsorbents are carbon based polymers. Examples could include:
- fibrous plant sources such as:
- oat hulls
- wheat bran
- alfalfa fibre
- extracts of yeast cell wall
- cellulose
- hemi-cellulose
- pectin
The efficacy of glucomannan-containing yeast products as mycotoxin adsorbents in feeds has been investigated globally with several studies with all animals [Click here to see in vivo research]. Research conducted in France at the National Institute for Agricultural Research (INRA) identified four Saccharomyes cerevisiae yeast strains that differed greatly in their glucan/mannan ratio. It was found that large differences existed in adsorptive capacity between the yeast strains with the amount of mycotoxin adsorbed strongly related to the beta-D-glucan content. This research confirms earlier work carried out in Alltech which led to the selection of a yeast strain high in insoluble beta-D-glucan content for the design and production of glucomannan-containing yeast product. (A. Yiannikouris et al., 2004) Advanced molecular techniques were used to elucidate the spatial conformation and molecular sites of interaction between zearalenone and glucomannan-containing yeast product. Molecular modelling was used to locate the interaction sites. Both hydrogen bonds and van der Waal's stacking interactions were identified as key interactions between mycotoxins and glucomannan-containing yeast product (Figure A)
Figure A
(A. Yiannikouris et al., 2004; Biomacromolecules, 5:2176-2185)
Mycotoxin adsorbents offer an attractive short-term solution to the challenge of mycotoxin-contaminated animal feeds. The only complete solution to the mycotoxin challenge will be the long-term goal of eliminating mycotoxins from the food and feed chains through improved quality control based on better analytical techniques coupled with genetic advances in plant resistance to fungal infestation.
If you are considering adding a mycotoxin adsorbent to your feed you need to look for the following:
- Proven efficacy in vivo as well as in vitro
- Low effective inclusion rate
- Stable over a wide pH range (This is necessary so that the mycotoxin stays attached to the adsorbent throughout the gut and is excreted.)
- High affinity to adsorb low concentrations of mycotoxins
- High capacity to adsorb high concentrations of mycotoxins
- Ability to act rapidly before the mycotoxin can be absorbed into the blood stream.
