Study On The Effect And Mechanism Of Photocatalytic Reduction Of Deoxynivalenol In Beer Malt By Graphite Phase Carbon Nitride Based Homojunction

Barley malt is the main raw material of beer production,and it is easy to pollute Fusarium graminearum（F.graminearum）and its deoxynivalenol（also known as vomiting toxin,DON）in the production process,which leads to beer quality problems and safety risks.In this paper,graphitic phase carbon nitride（g-C₃N₄）,which was visible light response,safe,cheap and easy to scale production,was further improved by oxygen doping,protonation modification and composite construction strategies,so as to prepare g-C₃N₄based homogenous composites.It was applied to reduce DON accumulation in malting process.At the same time,the enhancement mechanism of photocatalytic performance of g-C₃N₄homojunction,the mechanism of photocatalytic inhibition of F.graminearum growth,the structure and cytotoxicity of DON photodegradation products were systematically analyzed,which provided theoretical support for the photocatalytic reduction of DON in barley malt by g-C₃N₄homojunction.The main results are as follows:（1）The g-C₃N₄based homojunction（CNH/OCN-50）was prepared by protonated g-C₃N₄（CNH）and oxygen-doped g-C₃N₄（OCN）,and the mechanism of photocatalytic enhancement of CNH/OCN-50 was elucidation through microstructure characterization,photocatalytic experiments,optical properties characterization and free radical trapping experiments.The results demonstrated that oxygen doping can enhance the optical absorption range of g-C₃N₄and the separation efficiency of photogenerated electron-hole pairs,and proton doping can inhibit the recombination of photogenerated electron-hole pairs in g-C₃N₄.On the other hand,the electrostatic combination of CNH and OCN promoted the formation of homojunction at the interface,further inhibited the recombination of photogenerated electron-hole pairs,and improved the photocatalytic performance of CNH/OCN-50.Based on these findings,under visible light irradiation,the reaction rate constant for DON degradation by CNH/OCN-50 was 1.23 times that of OCN,1.49 times that of CNH,and 3.29 times that of g-C₃N₄.Furthermore,the ability to mycelial and spore growth inhibiting of F.graminearum by CNH/OCN-50 was also stronger compared to g-C₃N₄,CNH,and OCN.（2）The main factors and the photocatalytic inhibition mechanism of F.graminearum growth by CNH/OCN-50 were systematically analyzed.The results showed that under visible light irradiation,the free electrons excited by CNH/OCN-50 reacted with O₂in the photocatalytic system to produce a large amount of superoxide anion radical,which destroyed the cell membrane of F.graminearum,enhanced the permeability of cell membrane,leaked macromolecules such as nucleic acids and proteins,seriously disturbed intracellular metabolic activities,and finally significantly reduced the growth activity.When the catalyst concentration was 0.2 mg·m L^-1,the light intensity was 250 W and the light time was 140 min,the inhibition rate of spore growth reached 100%.And when the light time was extended to200 min,the mycelial inhibition rate reached 100%,thus blocking DON generation.（3）This study analyzed the influencing factors of the DON photocatalytic degradation by CNH/OCN homojunction and assessed the cell safety of its degradation products.The results showed that under visible light irradiation,the excited free electrons generated by CNH/OCN-50 effectively catalyzed H₂O₂in the system,leading to the production of a substantial amount of hydroxyl radical,thereby destroying the toxic structure of DON such as C₁₂,₁₃-epoxy and C_9,10double bond.Under the optimal conditions of catalyst concentration 0.4mg·m L^-1,light intensity 250 W,light time 180 min,H₂O₂concentration 30 mmol·L^-1,and the degradation rate of DON was 100%.The biological safety of DON degradation products was assessed using Hep G2 cells as a model.The results revealed that the toxicity of DON to Hep G2 cells was effectively eliminated after photodegradation,.（4）Taking barley contaminated by F.graminearum as the research object,the accumulation of DON during malting was reduced by CNH/OCN-50 photocatalysis,and the effect of photocatalysis on the brewing quality of barley malt was systematically studied.The results demonstrated that when there was no H₂O₂,CNH/OCN-50 inhibited the growth of F.graminearum and reduced the production of DON,and the DON content in high,medium and low pollution barley malt was reduced to 83.39%(415.20μg·kg^-1),93.95%(59.25μg·kg^-1)and 98.91%(5.25μg·kg^-1)of the original barley,respectively.In the presence of H₂O₂,CNH/OCN-50 can directly degrade DON in raw barley,and the DON content in high pollution barley malt can be significantly reduced to 96.06%(98.25μg·kg^-1)of the original barley,and the DON content in medium pollution and low pollution barley malt can be reduced to below the detection limit(≤0.25μg·kg^-1).At the same time,CNH/OCN-50photocatalytic reduction technology had good applicability in different varieties of barley,and had no adverse effect on the brewing quality of barley malt.