Effect Of Chlorine Dioxide ?ClO₂? On The Pathogenicity And Toxicity Of Penicillium Expansum

As a food additive,chlorine dioxide?ClO₂?has been widely used in the preservation of fruits,vegetables and aquatic products.At present,the research on ClO₂is generally focused on the fresh-keeping,bacteriostasis and bacteriostasis mechanisms.However,little research has been done on the inhibition of ClO₂ on post-harvest pathogenic fungus and patulin which is the secondary metabolite of Penicillium expansum.In this study,the distribution of patulin in different varieties apples were studied firstly,which could provide theoretical support for consumers and enterprises to use apples safely.Then,the inhibitory effect of ClO₂ on Penicillium expansum which is postharvest pathogen in vitro and in vivo was explored,and the degradation ability of ClO₂ to patulin was also evaluated.In order to further study the mechanism of ClO₂reducing patulin content,the inhibition effects of ClO₂ on the morphology of cell membrane,cell membrane permeability and spore activity,hodamine 123 staining,metabolic capacity were investigated;the expression of genes related to patulin synthesis was detected by real-time fluorescent quantitative PCR,thereby,the role of ClO₂ in the pathway of patulin synthesis was analyzed.The experimental results show that:1.By exploring the distribution of patulin in apples,it was found that patulin was not only found in the rotten parts of apples,but also detected in the non-rotten parts;The pathogenicity of Penicillium expansum was affected by the pH value of apple tissues such as the diameter of apple lesions,the number of Penicillium expansum in the same parts and the content of patulin were positively correlated with the pH value of apple tissues.The experimental results provide a theoretical basis for explaining the role of fruit tissues environmental pH value in the prevention of fungal infection,and provide guidance for the safe edible apples as well as the establishment of processing technology for rotten apples in apple products manufacturing enterprises.2.The mycelial growth of Penicillium expansum was studied by means of drug-containing medium,and it was found that ClO₂ could inhibit the mycelial growth of Penicillium expansum,400 mg L^-11 ClO₂ can completely inhibited the growth of Penicillium expansum;ClO₂ was applied to the study of preventing the decay of fruit by damage inoculation,and it was found that ClO₂ could also inhibit the rot of apple fruit to a certain extent;In addition,the related quality indexes of apple were determined to prove that ClO₂ could effectively prolong the apple fruits storage and then indicated ClO₂ could apply to the preservation and fresh-keeping of apple fruits.From the determination of the patulin content of in apple fruit and liquid culture medium found that ClO₂ could inhibit the content of patulin in apple fruit and liquid culture.3.Scanning electron microscopy?SEM?showed that ClO₂ treatment could change the morphology of the mycelium surface of Penicillium expansum and maked it rough and dry.After 350 mg L^-1ClO₂ treatment,the mycelium surface of Penicillium expansum was found to be adherent and collapsed seriously,and the boundary of the mycelium surface became blurred.After PI staining,the spore mortality rate in ClO₂treatment was about 98.21%,while that in control group was only 10.35%,it was significantly higher than that of the control group.After Rhodamine 123 staining,the fluorescence intensity of control group was 141.72,and that of ClO₂ treatment was336.52,which was 2.37 times higher than that of control group.This indicated that ClO₂treatment reduced the membrane potential of mitochondria,resulting in damage to mitochondria of Penicillium expansum spores and apoptosis of cells.The content of MDA malondialdehyde in the mycelium of Penicillium expansum was positively correlated with the increase of ClO₂ concentration,which indicated that ClO₂ could cause membrane lipid peroxidation and damage cells.Through the Congo red staining experiment,it was found that ClO₂ inhibited the metabolic level and the ability to produce patulin.4.Real-time fluorescent quantitative PCR was used to detect the expression of genes related to patulin biosynthesis and analyze the role of ClO₂ in the pathway of patulin biosynthesis.Overall,ClO₂ can affect the expression of 15 genes?PePatA^PePatO?,which indicated that ClO₂ can reduce the production of patulin by controlling the patulin synthesis pathway in Penicillium expansum.