Study On Reduction The Contamination Of Patulin And Its Producing Fungi In Apple Juice By Pulsed Light

Patulin is a mycotoxin produced by a variety of fungi,which has acute toxicity,chronic toxicity and cytotoxicity.Penicillium spp.is the main toxin producing fungi,which can cause the occurrence of apple blue mold,making the fruit soft and rotten.Due to its solubility in water and resistance to acid and heat,it is very easy to remain in the product after processing by traditional methods.In the production of apples and their products,patulin and its producing fungi have become an important factor affecting the development of apple industry and endangering human health.Therefore,it is of great practical importance to control patulin and its producing fungi in apple products.In this study,the fungicidal and detoxification treatment of five strains of patulin-producing fungi and patulin in apple juice was carried out with pulsed light as the core.And the mechanism of sterilization and toxin degradation products of pulsed light and their safety were investigated.The effects of pulsed light treatment on the quality and flavor substances of apple juice were investigated.To provide effective data and technical support for the control of patulin and its producing fungi.The following are the key findings and research results from this research.(1)The bactericidal effect of pulsed light on patulin-producing fungi in apple juice.Five strains of patulin-producing fungi mainly containing Penicillium expansum,Penicillium chrysogenum,and Penicillium griseofulvum were subjected to pulsed light treatment.The number of lethal flashes was investigated at different soluble solids contents(8-20 ~oBrix)and initial concentrations of microorganisms(10~4-10~6 CFU/m L),respectively.It was found that the survival rate of patulin-producing fungi gradually decreased with increasing the number of flashes and total fluxes.Increasing the soluble solids contents of juice and the initial concentration of microorganisms diminished the sterilization effect of pulsed intense light.In12 ~oBrix apple juice inoculated with 10~6 CFU/m L of target microbial inoculum,the colony counts of all five strains of patulin-producing fungi were below the detection limit(10CFU/m L)after 60 flashes by pulsed intense light(total fluence of 81.00 J/cm~2).(2)Mechanism of action of pulsed light inactivation of patulin-producing fungi.Fitting the inactivation process using bactericidal kinetic models with PBS as a substrate.The effects of pulsed light treatment on the appearance morphology and cell permeability were studied using scanning electron microscopy(SEM)and laser scanning confocal microscopy(LCSM).To explore the leakage of cell contents by pulsed light treatment.The findings demonstrated that the Weibull model was more suitable for fitting the inactivation kinetics on the patulin-producing fungi in PBS by pulsed light,and there was a trailing effect on the upward concave inactivation curve.SEM observed severe deformation and rupture of spores after pulsed light treatment,accompanied by leakage of cell contents.The loss of spore cell membrane permeability was observed by LCSM.The DNA and protein contents increased with the number of flashes.The above is consistent with the photophysical effect.The ATP and ROS contents increased and then decreased,probably because the pulsed light stimulated the mitochondrial electron transport chain inside the cell.The results indicated the role of the photochemical effect in the bactericidal process.(3)Degradation of patulin in apple juice by pulsed light and its safety evaluation.HPLC was used to determine the changes of patulin content in spiked apple juice samples treated with different pulsed light parameters.It was found that the degradation rate of patulin gradually increased with the number of flashes.When the toxin concentration in the juice was100μg/L,the toxin degradation rate increased from 31.88%to 90.57%during the course of 5to 25 flashes by pulsed light.For apple juice spiked samples(12 ~oBrix)containing 200μg/L patulin,the degradation of patulin could reach 96.27%at a light distance of 3.5 cm and 30flashes(corresponding to a total flux of 40.50 J/cm~2 and treatment time of 6 min 30 s).To more accurately describe the patulin degradation process,the quasi-first-order kinetic model was adopted(R~2>0.95).HRLCMS/MS showed that the lactone ring of patulin was disrupted to produce the less toxic desoxypatulinic acid.The cell assay showed that patulin’s toxicity to Hep G2 cells could be greatly reduced by pulsed light therapy.(4)Evaluation of pulsed light treatment on quality of apple juice.The changes in nutrients and flavor substances such as soluble solids content,p H,total acid,total sugar,total phenols,total color change,antioxidant activity,soluble sugars,and organic acids in apple juice were determined during pulsed light treatment.The results showed that with the treatment of pulsed light,there were no significant changes in soluble solids content,p H,and total sugar content in the basic physicochemical indexes.There was a slight increase in total acid content(3.39-3.49 g/L),while the total phenol content significantly decreased 19.15 mg/L.There was a significant difference in the total color difference of apple juice,which was in the range of"clearly visible".The total antioxidant activity,DPPH and superoxide anion scavenging rate of apple juice did not change,while the ABTS scavenging rate decreased significantly.The pulsed light treatment had a slight effect on the soluble sugars in apple juice,while the organic acids and aroma components changed more.Overall,the pulsed light treatment had some effect on apple juice quality but could maintain the basic physicochemical properties better.