GEOLOGICAL ORIGIN OF BENTONITE: ITS ROLE IN THE SELECTION OF POTENTIAL BINDERS FOR AFLATOXIN ADSORPTION

Since 2013, bentonite in the form of dioctahedral smectite is an additive authorised in the EU as a substance for the reduction of the contamination of feed by aflatoxins. Several studies indicate a big difference in the effectiveness of bentonites in sequestering aflatoxins. A clear correlation between mineralogical and physicochemical properties of bentonites and aflatoxin adsorption has not been well established. In this study, the most critical mineralogical, chemical, and physical properties that affect aflatoxin adsorption by bentonite were evaluated. Bentonite samples (29), mined from different locations around the world, were analyzed against the published selection criteria for aflatoxin adsorbents: mycotoxin adsorption parameters (maximum adsorption capacity and affinity) determined by the method of adsorption isotherms; pH; cation exchange capacity; particle size distribution; mineralogical/structural compositions; swell index and viscosity. A correlation between geological origin and AFB1 adsorption capacity was found (p<0.001). Sedimentary bentonites were significantly more effective than hydrothermal ones in adsorbing aflatoxin at different pH values. The extent of AFB1 adsorption by all samples was negatively and linearly correlated to the extent of desorption, and sedimentary bentonites were significantly more effective than hydrothermal ones in keeping bound the adsorbed fraction of the toxin (p<0.001). In addition, AFB1 adsorption by bentonites correlated positively with sodium content and swell index, but negatively with d001-value, magnesium and calcium contents. In conclusion, it seems that the geological origin of bentonite is a useful guide for the selection of a good binder for AFB1 reduction. Sedimentary bentonites containing sodium/swelling -smectite should be preferred to hydrothermal samples as potential aflatoxin binders. Taking into account the geographical origin of our samples, this approach should be applicable to bentonites worldwide.