Effect of Calcination on the Structure of Montmorillonite and Its Adsorption of Aflatoxin B1

Abstract

Aflatoxins are secondary metabolites primarily produced by Aspergillus flavus and A. parasiticus. Among them, aflatoxin B1 (AFB1) has garnered the most attention due to its toxigenic, mutagenic, and carcinogenic properties. Researchers worldwide have explored various strategies to mitigate the presence of these hazardous toxins. A practical approach to reducing AFB1 contamination is to add a clay, such as montmorillonite (MMT), as a toxin binder to animal feeds. Once MMT in the feed enters an animal's gastrointestinal tract, it adsorbs AFB1, reducing its toxicity and allowing the toxin to be excreted in feces, ultimately reducing the toxicity of AFB1 in the feed. To further enhance MMT’s adsorption of AFB1, heat modification of MMT is required. This heating process at temperatures of 300, 500, 700, and 900 °C, which is also known as calcination, alters the adsorption characteristics of AFB1. To assess the effect of calcination on the adsorption capacity of MMT to AFB1, modified and raw MMT samples were mixed with AFB1 at 100 ppb under constant agitation and incubated at 30 °C for 2 h at three different pH levels (pH 2.5, 5.2, and 6.6). High-performance liquid chromatography (HPLC) was utilized to determine the concentration of unbound AFB1. The results show that the MMT calcined at 300 °C exhibited the highest AFB1 adsorption, with binding capacities at pH levels of 2.5, 5.5, and 6.6 of 79.19%, 92.16%, and 91.55%, respectively. In contrast, raw MMT exhibited a lower adsorption of 66.46%. The improved adsorption after calcination is probably due to an increase in reactive surface area, an improved porosity, and
favorable electrostatic conditions. Characterization of the MMT using SEM, FTIR, XRD, and XRF confirmed the structural and surface modifications that occurred upon calcination. However, a high calcination temperature of 900 °C reduced adsorption capacity, which could be attributed to both structural degradation and decreased cation-exchange capacity. This study contributes to new areas by examining the interplay between pH and calcination temperature in AFB₁ binding by MMT.