Photocatalytic Degradation Of Patulin In Apple Juice Based On Nitrogen-Doped Chitosan-TiO₂ Nanoparticles And Its Safety Evaluation

Patulin(PAT)is a highly toxic fungal secondary metabolism,which is commonly found in rotten apples and their products.It is one of the main factors affecting the commercial value of apples and their products.The existing methods for degrading patulin in foods have some limitations.Therefore,it is of great significance to develop an efficient and safe method for degrading patulin in foods.In this paper,nitrogen-doped chitosan-TiO₂nanoparticle was used as photocatalyst to study the effect on the photocatalytic degradation of patulin in apple juice;The safety of this method was evaluated by analyzing the quality change of apple juice after degradation,and the cytotoxicity of the photocatalyst and the apple juice after degradation.UPLC-Q-TOF-MS was used to explore the intermediate products produced in the photocatalytic degradation process,speculate the possible degradation pathways and initially clarify the degradation mechanism,providing a new method and theoretical basis for the efficient degradation of patulin and the quality and safety of apple juice.The main findings are as follows:1.The precipitation method was used to prepare nitrogen-doped chitosan-TiO₂nanoparticles.And transmission electron microscope,X-ray photoelectron spectroscopy,scanning electron microscope,fourier Transform infrared spectroscopy,X-ray diffraction,BET surface area and ultraviolet-visible diffuse reflectance spectrum were used to characterize the structure of nitrogen-doped chitosan-TiO₂nanoparticles.The results showd that nitrogen-doped chitosan-TiO₂nanoparticles had a particle size of 20 nm and a lattice size of 0.268 nm.And the nitrogen atoms were successfully doped into the TiO₂crystal by combining with the oxygen holes in the TiO₂crystal to form N-O-Ti or Ti-N-O bonds.The formed N-TiO₂crystals were connected to the chitosan network structure through hydrogen bonds and coordination bonds,making its surface morphology rougher than TiO₂nanoparticles,increasing the specific surface area of TiO₂nanoparticles and improving the adsorption performance of TiO₂nanoparticles.In addition,nitrogen doping narrowed the band gap of TiO₂crystals,thereby enhancing the ability of TiO₂to absorb photoelectrons from the ultraviolet and visible regions.2.The photocatalytic effect of the synthesized nitrogen-doped chitosan-TiO₂nanoparticles was evaluated for the photocatalytic degradation of patulin.The results showed that the nitrogen-doped chitosan-TiO₂nanoparticles had an enhanced photocatalytic degradation activity of patulin compared with TiO₂nanoparticles.Photocatalytic degradation temperature and UV power were positively correlated with the photocatalytic degradation of patulin based on nitrogen-doped chitosan-TiO₂nanoparticles,while the addition of nitrogen-doped chitosan-TiO₂nanoparticles can only increased the effect of photocatalytic degradation of patulin within a certain range.The optimal conditions for the photocatalytic degradation of patulin based on nitrogen-doped chitosan-TiO₂nanoparticles were:the photocatalytic degradation temperature was 25?,the amount of catalyst added was 1.0 g/kg,and the power of UV lamp was 8 W.Under the optima conditions,it took 35 min and 45 min to completely degrade patulin in simulated juice and apple juice(250 m L)containing 500?g/kg patulin,respectively.Recycling experiments found that the synthesized nitrogen-doped chitosan-TiO₂nanoparticles had good reusability.3.By analyzing the changes in the sensory,physical and chemical indexes,and nutritional indexes of apple juice during the photocatalytic degradation of patulin based on nitrogen-doped chitosan-TiO₂nanoparticles,the effect of this treatment on the quality of apple juice was studied.The results showed that:photocatalytic treatment can significantly improve the color of apple juice(p<0.05),and there was no significant change in the taste of apple juice before and after photocatalytic treatment(p?0.05),but this treatment will have a certain impact on the aroma of apple juice.In terms of physical and chemical indicators,photocatalytic treatment will significantly increase the soluble solid content and the turbidity of apple juice(p<0.05),but had no significant effect on the p H and the titratable acid content of apple juice(p?0.05).In terms of nutritional indicatorsd,photocatalytic treatment had no significant effect on the content of reducing sugars and Vc in apple juice(p?0.05),but it will increase the content of total flavonoids in apple juice and decrease the content of total phenols slightly.4.Nitrogen-doped chitosan-TiO₂nanoparticles significantly improved the digestibility of TiO₂nanoparticles in the gastrointestinal tract(p<0.05).As the concentration of nitrogen-doped chitosan-TiO₂nanoparticles increased,the relative growth rate of Hep G-2 cells decreased,the toxicity level increased,the cell growth state became worse,cell morphology changed,cell membrane damage increased,mitochondria transmembrane potential decreased and the ROS content increased.But less than 100?g/kg nitrogen-doped chitosan-TiO₂nanoparticles had less toxic effect on Hep G-2 cells.After the apple juice containing a certain amount of patulin was detoxified by photocatalytic degradation,as the photocatalytic treatment time increased,the relative growth rate of Hep G-2 cells increased,the toxicity level decreased,cell morphology was good,the damage of cell membrane and mitochondria decreased,and the effect of oxidative stress decreased,the safety of apple juice after photocatalytic degradation was improved.5.The main active species in the process of photocatalytic degradation of patulin based on nitrogen-doped chitosan-TiO₂nanoparticles were analyzed.The degradation products and degradation mechanism were analyzed by using total organic carbon and UPLC-Q-TOF-MS analysis.The results showed that:hydroxyl radicals was the main active species in the photocatalytic degradation of patulin based on nitrogen-doped chitosan-TiO₂nanoparticles.Through UPLC-Q-TOF-MS analysis,two degradation products produced in the process of photocatalytic degradation of patulin were detected,and the molecular composition of these two degradation products were C₇H₆O₅and C₅H₆O₄by using the UNIFI Portal workstation software.The structures of these two degradation products were obtained by combining the ion fragment information in their secondary mass spectra with the Pubc Chem database.By exploring the possible pathways of photocatalytic degradation of patulin,it was analyzed that the degradation of patulin may be because the six-membered lactone ring of patulin was destroyed by hydroxyl radicals,the six-membered lactone ring was opened,and further oxidized and decomposed into small molecules of organic acids,and finally oxidized to CO₂and H₂O.