Contact Glow Discharge Electrolysis Inactivates Two Fungal Spores In Apple Juice And Its Effect On Juice Quality

Penicillium expansum and Trichothecium roseum are important pathogenic fungi,causing blue mold and pink rot in apples,respectively.Both fungi not only cause rot and quality deterioration,but also accumulate mycotoxins in the fruit.Apple juice is the most important product of apple.However,the apples used for juice processing are susceptible to bruises and other forms of mechanical damage during harvest and post-harvested handling,resulting in serious postharvest loss.During storage,the fruits are more susceptible to pathogenic infections,among which P.expansum and T.roseum are the most common fungi.Although the sorting system removes most decayed fruits with apparent symptoms,some may still enter the squeezing process,resulting in contamination of the juice with spores.Contact glow discharge electrolysis（CGDE）is a new plasma sterilization technique with high efficiency and without residue.However,its effect on the inactivation mechanism of fungi and the quality of apple juice remains unknown.In this study,the effects of treatment on the growth and pathogenicity of P.expansum and T.roseum were investigated.The parameters were optimized for inactivation spores,and the mechanisms involved in the inactivation of fungal spores were revealed.In addition,the effects of CGDE treatment on the quality,antioxidant properties and cytotoxicity of apple juice were evaluated.The results are as follows:1.Oxygen,nitrogen and air atmosphere had no significant effect on the critical voltage,however,which significantly affected the p H value and conductivity of the solution.With the extension of the treatment time,the p H value of the solution decreased significantly,and the conductivity first increased and subsequently declined.In addition,different gas atmospheres affected the types of active substances produced.H₂O₂,·OH and O₃ were produced in oxygen atmosphere,H₂O₂,·OH,NO₃^-and NO₂^-were produced in nitrogen atmosphere,and H₂O₂,·OH,O₃,NO₃-and NO₂-were produced in air atmosphere,which increased with the treatment time.2.CGDE treatment decreased the spore germination rate,biomass,and colony diameter of P.expansum and T.roseum.The treated spores had a rough surface,uneven,bulging cell morphology,damage to the cell wall,destruction of the continuity and compactness of the cell membrane,and the appearance of vacuoles.There were fewer conidia in the mycelium,and breakage and shrinkage of the mycelium appeared.In addition,the treated spores had less pathogenicity on the fruit.3.The results of transcriptome showed that there were 5628 differentially expressed genes in P.expansum spores compared with the control group,including 2861 up-regulated genes and 2767 down-regulated genes.KEGG enrichment results showed that the differentially expressed genes were mainly involved in oxidative phosphorylation,glutathione metabolism and other pathways.4.The inactivation efficiency of P.expansum and T.roseum spores in apple juice increased with the extension of treatment time and voltage and lower electrode gap.The inactivation kinetics of spores in apple juice was consistent with a first-order kinetic model.Moreover,after CGDE treatment,the amount of malondialdehyde in fungal spores increased,ergosterol synthesis was inhibited,intracellular reactive oxygen species accumulated,the cell membrane’s integrity was lost,nucleic acids and proteins leaked,and the integrity of the cell membrane was destroyed.5.The particle size,total soluble solids,reducing sugar and V_C content of applejuice treated with CGDE did not change compared with the control,while theζpotential and titratable acid increased.The L*values of the juice remained stable,while the a*and b*values decreased and△E*increased.In addition,the content of volatile compounds in apple juice increased,the content of esters increased,and the content of terpenes decreased after CGDE treatment.6.The contents of chlorogenic acid,caffeic acid,p-coumaric acid,quercitrin and proanthocyanidins in fruit juice decreased,the content of quercetin increased,the content of total phenols increased first and then decreased,and the total flavonoids decreased with treatment.The scavenging ability of ABTS,DPPH and FRAP of apple juice first increased and subsequently declined.In addition,the treated juice inhibited the proliferation of human hepatoma HepG2 cells and promoted apoptosis,but had little effect on HUEVC cells.In summary,CGDE could inactivate P.expansum and T.roseum spores in apple juice by producing ROS and RNS,resulting in inhibition of ergosterol synthesis,peroxidation of membrane lipids,and disruption of cell membrane integrity.Short-time CGDE treatment did not affect the quality of apple juice,but increased the volatile compounds content and antioxidant capacity.In view of its high efficiency in inactivation of fungal spores and little impact on fruit juice quality,CGDE has a huge application potential in the food industry.