| dc.description.abstract | Aflatoxins (AF), fumonisins (FB), ochratoxin A (OTA), deoxynivalenol (DON), and zearalenone
(ZEN) are the five major groups of agriculturally important mycotoxins produced by molds Fusarium,
Aspergillus, and Penicillium. They are naturally occurring mycotoxins and frequently found
in corn, wheat, barley, oat, tree nuts, rice, peanut, sorghum, hay, fruits, and other crops. Contamination
of food and feedstuff by mycotoxins is a worldwide problem and unavoidable despite
significant progress in preventing the growth of the fungi, developing more resistant crops, and
implementing biological control measurements. Preventing the health risks and economic losses
from mycotoxin contamination are crucial issues. Using clays or similar products as binders of the
mycotoxins is an attractive strategy for managing the mycotoxins. However, such a material has
not been discovered for fumonisin Bv1 (FBv1), OTA, DON, or ZEN. The objectives of this research
were to (1) select and modify natural smectites to optimize their binding efficiency for FB v1, OTA,
DON, and ZEN and (2) synthesize layered double hydroxides (LDHs) to bind FBv1.
Six smectites with different layer charged densities were chosen in this research to evaluate their
adsorption capacities for OTA, DON, and ZEN. The interlayer cation in smectites was replaced
with different hydration energy and valences to change the space between the hydrated cations and
thus match the size of the targeted mycotoxins. The surface hydrophobicity of the smectite was
increased by intercalating a cationic surfactant to enhance the adsorption capacities of ZEN and
OTA which had low water solubility. The effects of the ionic form of FBv1 were studied on smectite
and synthesized anionic adsorbent, layered double hydroxide, under various pH values.
Despite ZEN and AFBv1 shared high similarities in several aspects, the size-matching theory observed
in ABv1 between adsorbed molecules and smectites was not applicable to ZEN. The determinative
factor of ZEN adsorption was the hydrophobicity of the adsorbent, which can be indicated
by the charge density of smectites and Z?2/r value of exchange cations. Lacking highly negative
surface charge carbonyl oxygen and less planar structure of ZEN made the hydrophobic interaction
between carbonyl oxygen and smectite more difficult than AFBv1. Water-soluble DON showed
inverse responses to exchange cation and layer charge density of smectite on adsorption compared
to hydrophobic ZEN. Low OTA adsorption at neutral pH of the aqueous solution was attributed to
its ionic form.
FBv1 can be adsorbed onto interlayer of smectite at low pH and exhibited a decrease in affinity with
pH increased. Estimation of chemical species of FBv1 at various pH can help predict the adsorption
behavior of FBv1 based on the ionic form of FBv1 and charge type of adsorbent. Although FBv1 existed
mainly as the anionic form at pH 7, isothermal adsorption suggested adsorption of FBv1 was
still observed.
The charge density of Mg/Al LDHs significantly affected the FBv1 adsorption capacity through
varied the amount of adsorbing site. The FBv1 adsorption on Mg/Al LDHs was primarily driven by
the electrostatic interactions between the anionic part of FBv1 and the positive charge sites on LDHs.
Anion exchange of NO¯¯¯v3
or CO?2-/v
3 by FBv1 was the dominant adsorption mechanism. However,
increase in the amount of anionic FBv1 by raising the solution pH did not increase the adsorption
capacity as the competition between anionic FBv1 and OH? for adsorbing site was observed. | en |
