Study On Preservation Of Fresh Tremella By Curcumin-mediated Non-thermal Photodynamic Sterilization

Known as the "crown of bacteria" in the world,Tremella is a kind of high-quality medicinal and edible fungus.With high nutritional value including glial,amino acids,organophosphorus and other substances,fresh Tremella is reported to be benefial for humans.However,with the high water content of 75%-80%,the storage of Tremella is extremely difficult.The current research shown that the main food-borne pathogenic microorganisms causing the corruption of fresh white fungus and food poisoning are Pseudomonas aeruginosa.In this paper,the inactivation effect of PNST on P.aeruginosa and its mechanism of action were investigated.Meanwhile,the bacteriostasis effect on fresh Tremella treated by PNST and the quality of the product structure,physical and chemical properties were also evaluated.The content of this paper is as follows:(1)Identifying the dominant bacteria of the spoilaged white fungus floraThe dominant bacteria of spoilaged white fungus flora were analyzed using 16S r DNA,PCR amplification and BLAST sequencing.The results showed that the dominant bacterias were Microbacterium,Acinetobacter,Pseudomonas,Enterobacter and Citrobacter,while the main pathogen causing the corruption of fresh tremella was P.aeruginosa.(2)Study on the inactivation effect and its mechanism of PNST on P.aeruginosaThe inactivation effect of Non-thermal photodynamic sterilization technology(PNST)using curcumin as photosensitizer on P.aeruginosa was investigated.The membrane damage of P.aeruginosa by PNST was analyzed by scanning electron microscopy(SEM)and transmission electron microscopy(TEM)observation as well as the conductivity of broth,cytoplasm leakage,and DiBAC4(3)membrane potential.Agarose gel electrophoresis and Tunel method were used together to evaluate the DNA damage of P.aeruginosa by PNST.The degradation of total protein and the specific protein of P.aeruginosa treated by PNST were analyzed by SDS-PAGE and LC-MS/MS.Results shown that polymyxin B(5%)with curcumin(100μM)under LED light for 30 min exposure can significantly inactivate the P.aeruginosa with the inhibition rate of 99.99%.And the mechanism study shown that the conductivity,OD260 and OD280 of bacillus of P.aeruginosa were significantly increased after PNST treatment.Fluorescence of PNST treated group was stronger than control group using DiBAC4(3)fluorescent probe.The Scanning electron microscopy and electron microscopy revealed that the cell membrane of P.aeruginosa was damaged after the PNST treatment.It also shown that the DNA was significantly damaged after PNST treatment through DNA electrophoresis and Tunel assay.Finally,it also shown that most of the protein were degraded after PNST treatment through the analysis of protein electrophoresis,only 30S ribosomal protein,recombinant protein,glycerol kinase and nitrate reductase identified by the LC-MS/MS existed after the PNST treatment.(3)Preservation effect on fresh Tremella by PNSTInactivation of the total colonies number of fresh white fungus by photodynamic non-thermal sterilization with curcumin as photosensitizer at 28℃ was studied by bacterial plate colony counting method.At the same time,sensory evaluation and physical as well as the chemical indicators of fresh white fungus before and after photodynamic therapy were evaluated.The results showed that the photosensitizer concentration of 40 μmol/L under 60 min exposure by the LED light achived the best bactericidal effect on fresh Tremella.The inactivation rate of bacteria in fresh Tremella reached 99.9%.The sensory quality and nutritional characteristics of Tremella fuciformis were not influenced which could meet the needs of consumers.