ISOTHERM MODELING OF ORGANIC ACTIVATED BENTONITE AND HUMIC ACID POLYMER USED AS MYCOTOXIN ADSORBENTS
Résumé
The aim of the current study was to evaluate and to compare two representatives of different classes of adsorbents, intended for use as a feed additive to prevent or reduce adverse effects exerted by mycotoxins, specifically Ochratoxin A and Zearalenone. The adsorbents, an organically activated bentonite (OAB) and a humic acid polymer (HAP) were tested in a common in vitro model with a pH course comparing the maximum pH changes that can be expected in the digestive system of a monogastric animal, i.e. pH 7.4 for the oral cavity, pH 3.0 for the stomach, and pH 8.4 for the intestines. In the 1st experiment, the concentration-dependent adsorbent capacity of OAB and HAB were tested using a fixed concentration of either mycotoxin. Thereafter, adsorption was evaluated applying different isotherms models, such as Freundlich, Langmuir, Brunauer-Emmett-Teller (BET) and Redlich-Peterson, to characterize the adsorption process as being either homo- or heterogeneous, and represents either mono- or multilayer binding. At the recommended statutory level for the mycotoxins of 0.1 mg Kg-1 OTA and 0.5 mg Kg-1 ZEN, OAB showed an adsorbed capacity of >96% towards both mycotoxins, regardless of the pH. The HAP product was also able to absorb >96% of both mycotoxins at pH 3.0, but extensive desorption occurred at pH 8.4. Based on chi-square (Chi2) values, Langmuir and Redlich-Peterson equations proved to be the best models to predict monolayer equilibrium sorption of OTA and ZEN, onto the organically activated bentonite and the humic acid polymer. The applied methodology has a sufficient robustness to facilitate further comparative studies with different mycotoxins adsorbing agents.
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