Mycotoxin adsorption on organo zeolites

by Dr. Aleksandra Dakovic
Institute for Technology of Nuclear and Other Mineral Raw Materials
P. O. Box 390,11 000 Belgrade, Serbia and Montengro
-- currently visiting University of Missouri

ABSTRACT
Mycotoxins are a group of structurally diverse secondary fungal metabolites that occur as contaminants of grain worldwide. Many of these mycotoxins can cause serious problems in livestock resulting in substantial economic losses. The most common mycotoxins found in animal feed are the aflatoxins, ochratoxins, trichothecenes, fumonisins, and zearalenone. The most promising and economical approach for reducing mycotoxicosis is the utilization of adsorbents (natural zeolites and clays) in animal feed to bind the mycotoxins efficiently in the gastro-intestinal tract and prevent their absorption. The natural forms of these minerals effectively bind aflatoxins both in vitro and in vivo. Chemical modification of phylosilicate clays and zeolites with long chain organic cations results in an increased hydrophobicity of the mineral surface providing a high affinity for hydrophobic organic molecules, like the majority of the mycotoxins.

The physical properties of mycotoxins, like polarity, solubility, size, shape and in the case of ionized compounds charge distribution and dissociation constants play a significant role in the adsorption processes. We investigated the effects of surface coverage, solution pH and polarity of zearalenone (ZEN), ochratoxin A (OCHRA) and aflatoxin B1 (AFB1) on their in vitro adsorption by a natural zeolite -clinoptilolite modified with different ammounts of octadecyldimethylbenzyl ammonium (ODMBA) ions. The amount of ODMBA in organo zeolites was £ ECEC value of the starting zeolite. It was determined that specific active sites for fairly non polar ZEN and OCHRA were formed by adsorption of ODMBA on the zeolitic surface and that their adsorption increased with increasing hydrophobicity of the zeolitic surface. The highest adsorption was achieved at the monolayer coverage of the zeolitic surface with ODMBA. The adsorption of diphenolic ZEN on organo zeolites was not affected by solution pH. At lower surface coverage, the adsorption of ionizable OCHRA was highest at acidic pH while at higher surface coverage, the adsorption was practically independent of pH. In contrast, the adsorption of hydrophobic, nonionizable AFB1 on organo zeolites decreased with increasing hydrophobicity of the organo zeolite surface.

Furthermore, the highest adsorption of AFB1 was achieved on inorganic forms of zeolitic tuff at all investigated pHs, comfirming that the active sites at the hydrophilic zeolitic surface are relevant for its adsorption. Because, the investigated mycotoxins have similar water solubilities, the results are consistent with calculated dipole moments comfirming the organo zeolites were much more effective in adsorbing ZEN and OCHRA which possesses lower dipole moments than AFB1 which has the highest dipole moment. The results demonstrate that mycotoxins physical chemical properties have an influence on their adsorption on organo zeolites.