Protein interference on aflatoxin B1 adsorption by smectites in corn fermentation solution

Abstract

Corn is the main feedstock used for ethanol production in the United States. To reduce wastage and toxicity to human and animal, using aflatoxin contaminated corn in biofuel industry is thought to be rational. Yet up to three-fold of increment of the mycotoxins in the co-product have detrimental impact on animal health. It would be desirable to inactivate or to remove aflatoxins during fermentation of corn. Smectites were previously found to be highly efficient for aflatoxin B1 adsorption in ethanol and glucose solution, two major compounds in corn fermentation solution. The primary objective of the present study was to evaluate the aflatoxin B1 adsorption efficiency by smectites in real corn fermentation solution. The secondary objective was to identify any interfering compound that might hinder aflatoxin B1 adsorption. Aflatoxin B1 adsorption by smectites in fermentation solution was found to be low. A calcium smectite (3MS) had aflatoxin B1 adsorption capacity (Qmax) of 0.22molkg−1in the fermentation solution but 0.54molkg−1 in the aqueous solution. The Fourier transform infrared (FTIR) analyses indicated that some compounds from fermentation solution were adsorbed on the smectites and had irreversible bonding with the clay minerals. Those compounds competed with aflatoxin B1 for the adsorbing sites of smectites. The major infrared bands due to interfering compounds were at ~1653, 1532, 1451, and 1235cm−1. These bands appeared when smectites were added to either clean or aflatoxin B1 spiked fermentation solutions. Similar spectral bands were obtained after treating the smectites with zein, a major protein in corn. Thus, the major interfering compounds in fermentation solution were believed to be proteins. The XRD results proved the adsorption of the proteins in the interlayer of smectites. After heating at 300°C, smectites reacted with fermentation solution had d-spacing of at least 15Å, whereas the pure smectites collapsed to ~10Å. This reflected great interferences of the compounds, most possibly proteins on aflatoxin B1 adsorption by the smectites. However, despite of strong interferences, adsorption experiments suggested that smectites were still able to adsorb aflatoxin B1 to some extent. Presence of characteristic aflatoxin B1 bands at ~1595, 1383, 1362, 1304, 1272, and 1205cm−1 on smectite complexes treated in fermentation solution revealed the existence of the mycotoxins on the clay minerals. Strategies should be taken to enhance the selectivity of smectites for the aflatoxins in corn fermentation solution.