Mycotoxin Detoxification And Its Transformation Mechanism In Edible Oil Refining Processes

Mycotoxin contamination of is one of the important issues related to the quality and safety of edible oils.It has been estimated that 60-80%of oilseed crops worldwide are contaminated with mycotoxins,resulting in economic losses of billions of dollars annually.Researching on the transformation mechanisms of mycotoxins in edible oils refining processes and the new technologies for detoxification is of great theoretical and practical significance.To understanding the transformation mechanisms of mycotoxins in edible oil processing,the structure,distribution,and toxicity of the transformation products of mycotoxins in the traditional edible oils refining processes were elucidated in this dissertation.Secondly,physical adsorption method by using Zr-based metal-organic framework（MOFs）as a novel adsorbent was proposed for efficient removing aflatoxin B₁（AFB₁）from peanut oil.Moreover,in-situ efficient degradation of AFB₁ was achieved by using a Fe-based MOFs adsorbent through the Fenton-like reaction.Aiming at AFB₁ contamination in strong flavor peanut oil,a novel technology of enzymatic directed detoxification of AFB₁ using amphiphilic laccase nanoflowers the biocatalyst was proposed.The main research methods and conclusions are as follows.（1）Using peanut oil as the matrix,the laboratory-scale peanut oil pressing and refining process was simulated to study the transfer and transformation of AFB₁ in peanut oil refining.Results showed that 12.9%of the added AFB₁ was transferred to the by-products in the refining process,87.1%of AFB₁ was transformed to the lactone ring opened product（OP-AFB₁）,and no AFB₁ was detected in the refined peanut oil.Both transfer and transformation of AFB₁ occurred mainly during the deacidification stage,and due to the increased polarity of OP-AFB₁,it was transferred to the soap stock by-product during the refining process.However,OP-AFB₁ in soap stock will spontaneously dehydrate and close lactone ring to restore the parent structure under acidic conditions.Therefore,Fenton reaction was further used to completely mineralize the AFB₁ transformation product into non-toxic carbon dioxide and water.（2）Using rapeseed oil as the matrix,a laboratory-scale rapeseed oil pressing and refining process was simulated to study the transfer and transformation of OTA in rapeseed oil refining.Results showed that 16.25%of the added OTA was transferred to the by-products in the refining process,83.75%of OTA was transformed to the lactone ring opened OTA（OP-OTA）in the deacidification stage,and both OTA and OP-OTA were not detected in the refined rapeseed oil.Cell toxicity experiments and in silico toxicity estimation results show that the transformation product still has strong renal cell toxicity,developmental toxicity,and bioaccumulation risk.（3）MOFs（PCN-224,MIL-101（100）,ZIF-8）as novel adsorbent is proposed for efficient removal of mycotoxins in edible oil.By measuring the specific surface area,pore size and pore volume of MOFs,it was concluded that the pore size and specific surface area of the adsorbent determines the adsorption efficiency.The adsorption isotherm showed that the maximum adsorption capacity of PCN-224 for AFB₁ was as high as 185.29μg/mg,and the adsorption rate was extremely fast（reaching equilibrium within 5 minutes）.Mechanistic exploration shows that adsorption mainly relies on electrostatic attraction,hydrogen bonding,andπ-πconjugation.After seven cycles of adsorption-Fenton reagent regeneration,the AFB₁ adsorption efficiency of PCN-224remains as high as 98.91%.When PCN-224 was applied for the adsorption and detoxification of AFB₁ in peanut oil,it was found that 0.5 mg/g PCN-224 could detoxify AFB₁ contaminated peanut oil（100μg/kg）within 15 min to meet the national food safety limit standard,and the adsorbents had no obvious effect on the quality of peanut oil.（4）Fe-based MOFs（Fe-PCN）as catalyst is proposed for efficient in-situ degradation of mycotoxins through Fenton-like reaction.The effects of catalyst size,H₂O₂ concentration and reaction time on the degradation efficiency of AFB₁ were investigated.Results showed that as the particle size of the Fe-PCN increases,the specific surface area increases,and the total removal rate of AFB₁ increased from 39.71%to 91.38%.While,the pore size decreased from 7.46 nm to 2.76 nm,resulting in the proportion of degraded AFB₁ decreased from 84.81%to 48.15%.The results indicate that the appropriate pore size was conducive to substrate adsorption and product release（release the catalytic active sites）.Under the optimal catalytic condition,only 0.15mg/m L Fe-PCN₁₅₀ was required to remove 92.83%of AFB₁（1μg/m L）,and 73.37%of AFB₁ was degraded.Mechanistic exploration showed that hydroxyl radical and singlet oxygen were the main active oxygen species for catalytic degradation of AFB₁.（5）To address the bottleneck issue of physical adsorption and chemical degradation that destroys the nutritional and flavor components of edible oils,a novel amphipathic laccase-inorganic hybrid nanoflower（Lac NF-Con A-P）biocatalyst was developed for targeted degradation of AFB₁ in fragrant peanut oil.Benefited from the retention of necessary water on the enzyme molecule surface by amphiphilic polymerization and the improved dispersion of catalyst at the oil-water interface,the turnover frequency of the Lac NF-Con A-P was increased by 134 times and 3.2 times compared to free laccase and immobilized laccase,respectively.Practical tests showed that only 0.625 mg/g catalyst was needed to detoxify AFB₁ contaminated peanut oil（200μg/kg）to meet the food safety limit standards set by various institutions or countries within 3 hours,and almost no impact on the quality of peanut oil.Thereupon,this proposed amphiphilic catalyst opened up new avenues for the development of novel biocatalysts for mycotoxin detoxification in edible oils.