Molecular Mechanism Of Alternaria Toxin Tenuazonic Acid From Citrus Juice By Inactived Microbial Cells

Tenuazonic acid(TeA)is one of toxic metabolite produced by Alternaria spp.,Phoma sorghina and Pyricularia oryzae.It is regarded as the Alternaria mycotoxin with the highest acute toxicity,which can inhibit protein biosynthesis by suppression of the release of new proteins from the ribosome.Citrus fruit is susceptible to pollution by Alternaria during growth and post-harvest storage.At present,a large number of studies have reported that TeA has been detected in citrus and their products.Therefore,it is urgent to study the detoxification of Alternaria toxins from citrus juice,which can promotes the development of human health and citrus industry,and lay a foundation for formulating limit standard of Alternaria toxins.In recent years,biosorption technology has attracted much attention due to its potential application as a safe and efficient method for controlling and removing mycotoxin decontamination.The main results of this study are as follows:1.5 strains of lactic acid bacteria and 3 strains of yeast were selected out for TeA removal experiment based on relevant literature,a strain of Lactobacillus brevis(CICC20023)with highest TeA removal efficiency was screened for next step.The results showed that 0.2g of freeze-dried bacteria powder removed more than 30% of TeA in 10 ml water solution containing initial TeA concentration is 1000μg/L within absorbtion of 24 h.2.The optimal conditions for adsorption removal of TeA from citrus juice using Box-Behnken design and response surface method were adsorbent dosage of 1.20 g inactive cells in 20 mL citrus juice,adsorption time of 11.43 h,initial TeA concentration of 250μg/L and pH of citrus juice of 3.15.Under the optimal conditions,adsorption removal rate of TeA from citrus juice was 87.87%.In addition,the model established by response surface quadratic progression between the four factors and removal rate of TeA had a good fitting accuracy,and the theoretical value was basically in agreement with the actual value.3.The TeA adsorption process of inactivated cells was studied by thermodynamics and kinetics models.The research results showed that the pseudo two order kinetic model was more suitable to describe the adsorption process,and the adsorption process was a kind of chemical adsorption.The adsorption thermodynamics results showed that Langmuir model was more suitable for the simulation of adsorption process than the Freundlich model.4.Finally,the adsorption mechanism of TeA using various modified inactivated cells was investigated.The TeA-exposed bacterial cells and TeA-unexposed bacterial cells were characterized by Scanning Electron Microscopy coupled with Energy Dispersive X-Ray Spectroscopy(SEM-EDS),Transmission Electron Microscopy(TEM)technique,Transform Infrared Spectroscopy(FTIR),XRD and Zeta potential methods.The results showed that the inactived cells had the capacity to adsorb Te A from aqueous solution.The formaldehyde-treated and methanol-treated biomasses significantly increased the TeA adsorption rate.The results of SEM-EDS and TEM showed that increasing the surface area of the cell wall could improve the adsorption capacity of TeA,and an ion-exchange reaction has appeared during adsorption process.From the results of FTIR and XRD,the C-O,O-H and N-H groups from some protein and carbohydrate components in the cell walls,were obviously involved in the adsorption of TeA.The Zeta potential results showed that TeA adsorption was caused not only by the cell wall but also by the bacteria cell surface charge.