Antimicrobial Effect Of Catalytic Infrared And Intense Pulsed Light On Dry Green Sichuan Pepper And Its Synergistic Mechanism

Green decontamination of dry granula with uneven surface is one of the bottlenecks in dehydrated fruit and vegetable industry.Conventional technology can not keep the flavor and safety of foods due to overheating effect,harmful residue,liquid medium,and other reasons.In this paper,dry green Sichuan pepper（DGSP）was used as the experimental object,which was one of the common ready-to-eat granular spices with volatile components and significant shadow structure.A combination method was used for the sterilization to DGSP.Taking advantage of the cold and rapid sterilization of intense pulsed light（PL）,the problems such as long time,high energy consumption,low safety,decline in quality were overcome.At the same time,the shallow surface thermal effect and long wave diffraction effect of catalytic infrared（CIR）were used to overcome the problem that the wrinkled shadow structure on DGSP restricted the sterilization of PL.In this paper,the bactericidal characteristics and mechanism of the methods on a single bacterium were researched respectively,and combined with the actual bactericidal effect on DGSP,the synergistic mechanism of the combination method was explained.The specific research contents and results are shown as follows:（1）Flavor quality and microbial contamination of DGSPThe methods such as electronic nose,colorimeter,UV spectrophotometry determination were used to evaluate the flavor quality of DGSP from 10 areas,such as odor,color and total alkaloid content.The total aerobic bacteria and molds on DGSP were detected by plate counting method,so as to provide necessary reference and quality evaluation indexes for the decontamination of DGSP.The results showed that there were significant difference in the flavor characteristics of first-grade product in different regions,and the aerobic bacterial counts were higher than the current hygienic standard.10 bacterial strains and 3 fungal strains were identified from DGSP by universal primer PCR technology,and Pseudomonas aeruginosa was selected as the research target of later experiments.High throughput sequencing combined with big data analysis technology was used to study the macro structure on DGSP,and speculate the possible source of contamination and the structural characteristics of flora,so as to provide reference for the selection of decontamination methods.（2）Bactericidal effect to Pseudomonas aeruginosa with CIR and PLPseudomonas aeruginosa was used as a target bacteria in this chapter,the key process and environmental factors of CIR and PL were investigated,and the feasibility of the combination was verificated by inactivation of different microorganism.The results showed that the bactericidal effect of CIR was affected by temperature and water primarily,and a colony count decrease from 0.17 to 2.6 Log on DGSP was obtained by CIR for 1～4 min,which was close to that on the plate.The bactericidal effect of PL was affected by pulse energy primarily,which was little influenced by the operating environment,but showed weak on DGSP（the sterilization rate was 0.17 to 2.6 Log by PL for 10～50 s）.After a pretreatment of CIR for 2 min,a decrease of 2.81 Log on DGSP was obtained by PL for 50 s.At same dose,CIR and PL showed different inactivation effects on different microorganisms,it was an explanation to complementary of CIR and PL.（3）Inactivation mechanism of Pseudomonas aeruginosa with CIR and PLPseudomonas aeruginosa was used as a target bacteria,the changes of cells structure after CIR,PL and synthetise were studied at the cellular and subcellular levels.The changes of cell swimming power,cell death,cell membrane integrity,intracellular macromolecular leakage,membrane permeability,membrane fluidity and intracellular calcium ion were observed or measured by fluorescence microscopy,live cell imaging system,TEM,UV spectrophotometer,flow cytometry and polarization fluorescence spectrophotometer.The changes of intracellular protein and DNA were observed using SDS-PAGE and RAPD-PCR.The results show that the inactivation effect was mainly by destroying the cell membrane of Pseudomonas aeruginosa with CIR,and was mainly by damaging the intracellular protein and DNA with PL.In summary,the mechanism of different inactivation effects of the two technologies on different microorganisms was explained.（4）Effects of mixed flora on DGSP with CIR and PLThe bactericidal effect to a microorganism and a mixed flora could be different.In this section,the plate counting method was used to investigate the overall decontamination effect of CIR combined with PL on complex microorganisms,and RNA reverse transcription combined with second-generation sequencing technology was used to characterize the effect of bacterial community structure on DGSP.The results showed that the bactericidal effect of PL on DGSP was increased after pretreatment of CIR,and PL could decrease the applied dose of CIR.After CIR treatment for 3 min（70℃,9.5 cm）and PL for 50 s(1Hz,500 J·s^-1,9 cm),the total aerobic bacteria on DGSP could be reduced by about 3.0 Log.CIR could significantly cause the change of flora structure on DGSP,and the degree could be decreased after PL alliance,which probably stemmed from increase of inactivation effect on different bacteria.In addition,the prediction of cell function showed that CIR and PL were effectively complement each other.（5）Effects of CIR and PL on the quality of DGSPIn this section,the effects of CIR,PL and their combination on the color,volatile oil content,odor and total alkaloids of DGSP were investigated,and the changes of volatile components and hemp flavor components were further determined by GC-MS and UPLC-MS-MS.The results showed that the color and volatile oil content of DGSP were apt to affect by CIR that the treatment dose was suitable within 5 min,and the total alkaloids and hemp components changed a little.The degree above would be reduced after PL alliance.In addition,the total reducing power,·OH^-and ABTS+·clearance of DGSP after the treatment were measured successively.The results showed that CIR significantly affected the total reducing power and·OH^-clearance of DGSP,while PL significantly affected the ABTS+·clearance.The degree would be reduced respectively when combined the two methods.