Abstract
Clays are known to have promising adsorbing characteristics, and are used as feed additives to overcome the negative effects of mycotoxicosis in livestock farming. Modification of clay minerals by heat treatment, also called calcination, can alter their adsorption characteristics. Little information, however, is available on the effect of calcination with respect to mycotoxin binding. The purpose of this study was to characterize a Tunisian clay before and after calcination (at 550 °C), and to investigate the effectiveness of the thermal treatment of this clay on its aflatoxin B1 (AFB1), G1 (AFG1), B2 (AFB2), G2 (AFG2), and zearalenone (ZEN) adsorption capacity. Firstly, the purified clay (CP) and calcined clay (CC) were characterized with X-ray Fluorescence (XRF), X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR-IR), cation exchange capacity (CEC), specific surface area (SBET), and point of zero charge (pHPZC) measurements. Secondly, an in vitro model that simulated the pH conditions of the monogastric gastrointestinal tract was used to evaluate the binding efficiency of the tested clays when artificially mixed with aflatoxins and zearalenone. The tested clay consisted mainly of smectite and illite. Purified and calcined clay had similar chemical compositions. After heat treatment, however, some changes in the mineralogical and textural properties were observed. The calcination decreased the cation exchange capacity and the specific surface, whereas the pore size was increased. Both purified and calcined clay had a binding efficacy of over 90% for AFB1 under simulated poultry GI tract conditions. Heat treatment of the clay increased the adsorption of AFB2, AFG1, and AFG2 related to the increase in pore size of the clay by the calcination process. ZEN adsorption also increased by calcination, albeit to a more stable level at pH 3 rather than at pH 7. In conclusion, calcination of clay minerals enhanced the adsorption of aflatoxins and mostly of AFG1 and AFG2 at neutral pH of the gastrointestinal tract, and thus are associated with protection against the toxic effects of aflatoxins.
Highlights
Mycotoxins are secondary metabolites produced by toxigenic fungi growing on a wide range of agricultural products [1]
X-ray Fluorescence (XRF) analyses revealed that purified native clay (CP) and its calcined form (CC) were mainly composed of silicon dioxide (SiO2), aluminum oxide (Al2 O3 ), calcium oxide (CaO) and iron oxide (Fe2 O3 ) (Table 1)
The occurrence of magnesium oxide in both samples can be due to the presence of smectite, and to a small amount of dolomite, which is confirmed by the results of X-Ray Diffraction (XRD)
Summary
Mycotoxins are secondary metabolites produced by toxigenic fungi growing on a wide range of agricultural products [1]. The Food and Agriculture Organization (FAO) of the United Nations stated that nearly 25% of the cereal products is contaminated with mycotoxins [2]. AFs are a group of heterocyclic metabolites that are mainly produced by members of the genus Aspergillus, contaminating agricultural commodities. Aspergillus fungi are both found in the field as storage pathogens, the AFs’ content is omnipresent, but with a tendency to increase during storage [5,6]. AFs reduce the growth rate, decrease egg production, induce changes in organ weight, and increase the risk of disease [4]. AFB1 comprise a greater potency associated with the cyclopentenone ring of the
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