Inactivation Of Water-Soluble Curcumin Photodynamic Technology On Aquatic Foodborne Bacterial Pathogens And Norovirus

As an important nutritional and functional food source for human beings,aquatic food is susceptible to contamination by water-borne pathogens such as Vibrio spp.and norovirus,causing the frequent occurrence of food poisoning,endangering the health of consumers,damaging the reputation of food processing enterprises,impacting the development of social economy.Screening safe and effective processing technologies for inactivation of foodborne pathogens without damage of food nutrition and function is of primary importance in the research field of food safety.The objectives of this thesis were to investigate the inactivation effects and mechanisms of water-soluble curcumin（WSC）photodynamic technology（PDT）on aquatic foodborne pathogens,Grimontia hollisae（Gh）,Vibrio alginolyticus（Va）and norovirus surrogates（murine norovirus（MNV）and feline calicivirus（FCV））in vitro,and to test the applicable feasibility of this technology in aquatic food industry,to provide a novel method for food safety control and technical support.The main results are as follows:1.WSC-PDT was highly effective for inactivation of aquatic foodborne bacterial pathogens.Gh and Va decreased by 7.98 lg（CFU/m L）and 7.80 lg（CFU/m L）respectively in the condition of incubation time for 10 min,WSC concentration of 100μM and LED（420 nm）illumination for10 min.The inactivation rate of Vibrio parahaemolyticus and Vibrio vulnificus by WSC-PDT was over 99.99%.2.WSC-PDT induced the production of a great amount of ROS（reactive oxygen species）and damaged bacterial protein and DNA.A remarkable rise of ROS level in Gh and Va was noticed,and the damage of both total bacterial DNA and protein was observed,but no obvious change of the chosen virulence genes was detected,after WSC-PDT treatment.3.Both WSC-PDT and methylene blue（MB）-PDT were effective for the inactivation of two tested human norovirus surrogates.WSC（100μM）in combination with blue LED（30min）reduced MNV and FCV titers of 1.01 and 2.37 lg TCID₅₀/100μL respectively.FCV lost total infectivity by 10μM MB combined with xenon lamp（30 min）.4.PDT damaged virus capsid protein and nucleic acid.The FCV capsid damage was observed after WSC-PDT treatment by transmission electron microscope,but no obvious change of MNV capsid was noticed.Complete damage of FCV ultrastructure was displayed,and the protein crosslinking occurred.PCR and agarose gel electrophoresis demonstrated that the integrity of MNV nucleic acid was damaged after WSC-PDT and the most severe region was 2675-3107.5.WSC-PDT could be used for the disinfection of aquatic food surface.WSC-PDT was more effective than alcohol-soluble curcumin（ASC）-PDT,evidenced by decreasing indigenous bacteria in grass carp fillet by up to 0.8 and 0.45 lg（CFU/m L）respectively.The total bacterial count in grass carp fillet inoculated with Gh and Va was reduced by 0.75 and0.61 lg（CFU/m L）respectively,after WSC-PDT treatment.Having incubated with photoactivated WSC for 96 h,murine macrophage cells（RAW 264.7）showed no cell viability loss.Results obtained in this thesis suggested that WSC-PDT can inactivate Gh and Va by inducing the production of ROS in bacteria to damage protein and genome,and this technology can be applied to the disinfection of aquatic food surface.PDT can inactivate MNV and FCV by causing the viral protein crosslinking,destroying the capsid and damaging viral RNA,indicating its possible inactivation of human norovirus.