Aflatoxin B1 Adsorption to Clays: pH and FTIR Spectra.

Aflatoxin B1 (AfB1) is a chemical compound (mycotoxin) produced by Aspergillus fungi in crops, such as corn and peanuts.  The compound is both toxic and carcinogenic to animals and humans.  Clay minerals, such as montmorillonite, added to feed have been shown to reduce aflatoxicosis in animals caused by contaminated feed.  Aflatoxin adsorption to clays during feed digestion can reduce toxin absorption by the animal and minimize or prevent toxicologic effects.  Feeding studies have shown that activated carbon is less effective than clays in reducing aflatoxicosis.  In this study, the effects of solution pH on AfB1 adsorption to clays and other materials were measured using batch adsorption isotherms and infrared spectra (FTIR-ATR) of clay/AfB1 were collected.  Enzyme-linked immunoassay techniques and UV spectrometry were used to measure AfB1 concentrations.  AfB1 adsorption to montmorillonite was greatest at pH 4, whereas adsorption to activated carbon was greatest at pH 7.  Keto-enol tautomerism of AfB1 might explain the effect of pH on adsorption.  The enol (C-OH) form of AfB1 might be more stable at low pH than the keto (C=O) form.  FTIR spectra indicate that adsorption of AfB1 to montmorillonite (SWy-2) displaced interlayer water and shifted the Si-O stretch band from 992 to 1012 cm^-1.  The SWy-2 octahedral OH and quartz band positions were unchanged, but the quartz bands were far more distinct. Shift of the Si-O band suggests AfB1 was adsorbed to the siloxane surfaces of montmorillonite.  No AfB1 band shifts were identified in the clay/AfB1 FTIR spectra.  IR bands from AfB1 C=O groups were evident, but no apparent bands from AfB1 enol-form OH groups.