The Application Of Photodynamic Non-thermal Sterilization Technology On Instant Jellyfish

Instant jellyfish is a ready-to-eat product which was made by salted jellyfish after a series of processing.In recent years,to improve the process performance of instant jellyfish products,the products’ bacteria counts could not meet the requirement of National standards with the decreasing alum adding amount.Although the traditional thermal sterilization technology can effectively inactivate the microbes,but it required high temperature conditions which would lead to the jellyfish quality changes,nutritional and value losses.It is necessary to develop the PNST(Photodynamic non-thermal sterilization technology)in instant jellyfish industry.This thesis aims to study the analysis of flora and the identification of dominant microorganism in instant jellyfish products.The inactivation effects,mechanism and application of PNST(Photodynamic non-thermal sterilization technology)with curcumin as the photosentisers against dominant microorganism in instant jellyfish products were investigated in this study,followed by analysis the characteristics of jellyfish products,such as texture and sensory.At last,the instant jellyfish products were evaluated for their shelf life by accelerated shelf-life testing(ASLT).The main research and results are summarized as follows:1.The flora analysis of instant jellyfish products within 3 months after production,and two dominant Gram-negative strains isolated from the instant jellyfish products were identified as Burkholderia by BLAST sequence alignment and phylogeneti tree.The result showed that the average total bacterial count of the products was 48000 cfu/g which were beyond the limit of National standards.More positive potential pathogens,such as the Coliform bacteria Salmonella,Bacilluscereus and coagulase-positive Staphylococcusaureus were not detected in the products.2.The inactivation effects,mechanism and application of curcumin with PNST against B.cepacia in instant jellyfish products were investigated in this study,through the SDS-PAGE,MALDI-TOF-TOF/MS,AGE(agarose gel electrophoresis)and LC-MS/MS.Curcummin-PNST showed significant inactivating effects on B.cepacia with lower concentration of EDTA-2Na(food grade).The viability of B.cepacia was approximately 3.183-log reduced by illumination for 30 min with tungsten-halogen lamp light under the presence of 100 μmol/L curcumin and 0.5%(v/w)EDTA-2Na(food grade).The bactericidal activity against B.cepacias howed dose-dependant manner with the concentration of curcumin and the duration of irradiation.Curcumin-PNST induced damage of cell membrane and the leakage of cytoplasm of B.cepacia as OD260 and OD280 of B.cepacia suspensions treated with curcum increased significantly compared with control group.SDS-PAGE,MALDI-TOF-TOF/MS and LC-MS/MS image showed that undegradable proteins’ bands were DNA-binding protein,2-oxoglutarate dehydrogenase,aconitate hydratase,ATP-dependent protein ribonucleotide reductase,porin,ribosomal protein,respectively.Damage of the deoxyribonucleic acid(DNA)and degradation of proteins of bacterial cells may be the possible mechanisms for Curcumin-PNST against the B.cepacia.3.The inactivation effects,texture characteristics and physicochemical properties of PNST in instant jellyfish products were investigated in this study.Results of Box-Behnken design showed that the optimal conditions for Curcumin-PNST on the preservation of instant jellyfish were:EDTA-2Na(food grade)0.021%(w/v),the presence of 109.62 μmol/L curcumin and illumination for 30 min under the LED light.Under the optimal conditions,the viability of B.cepacia reduced from 4.712 LogCFU/mL to 1.478 LogCFU/mL with the inhibition effect of 99%.The bioenrichment concentration of curcumin was approximately 0.00646±0.0002 mg/mL which conform to the state standards.To sum up,the curcumin-PNST in products’ processing can inhibit the bacterial growth to extend the products’ shelf life without affecting its sensory quality.4.Arrhenius theory and statistics were used to predict the shelf-life of flakes,which were based on the dynamic changes of products’ bacteria counts during storage at 28,33 and 38℃,respectively.According to Arrhenius model and statistical analysis,the shelf-lives of instant jellyfish products treated with PNST were about 360～367.5 days by being stored at 23℃.Therefore,this research efficiently resolves the problem of the excessive bacteria counts in instant jellyfish and can be expected to be widely used in food industry to ensure the food safety.