| As one of the most important food-borne pathogens in the world,Campylobacter jejuni often colonizes in the intestines of animals.As a result,the treatment and consumption of contaminated poultry meat lead to the transmission of Campylobacter jejuni,and the contamination amount of Campylobacter jejuni in chicken is sometimes as high as 106 CFU/g.The traditional control methods can not meet the requirements of food sterilization and preservation,so it is imperative to seek a new environmentally friendly food sterilization technology.Recently,electron beam irradiation has shown great potential for application in food sterilization and preservation because it is safe and sterilize thoroughly.In this study,the mechanism of electron beam irradiation on Campylobacter jejuni was studied in vitro.The irradiation model of Campylobacter jejuni on chicken meat was established and the irradiation parameters were optimized.Then it was applied to sterilize clinical chicken samples.Moreover,the effect of irradiation on chicken quality was evaluated,which provided new thought for further prevention and control of Campylobacter jejuni.1.Effect of electron beam irradiation on Campylobacter jejuni in vitroIn this paper,the killing effect of electron beam irradiation on Campylobacter jejuni was firstly studied.The concentrations of Campylobacter jejuni suspensions(NCTC11168,ATCC33560,81-176,M166 and C410)were about 1.0×109CFU/mL,and the doses of electron beam were 0.15,0.2,0.3,0.4 and 0.5 kGy,respectively.The dose-survival curve showed that the killing ability of electron beam irradiation on Campylobacter jejuni was significant effective.The results of comparison of different Campylobacter jejuni isolates D10 values showed that there was no significant difference among the sensitivity of different Campylobacter jejuni strains to electron beam irradiation(P>0.05).Secondly,the effects of electron beam irradiation on the biological characteristics of Campylobacter jejuni were studied.The results of bacterial motility test indicated that the motility of the treatment group was significantly weaker than that of the control group(P<0.01).The results of chemotaxis analysis showed that when using succinic acid and a-ketoglutarate as the chemoattractants,the chemotaxis ability of the treatment group was significantly stronger than that of the control group(P<0.01).The results of scanning and transmission electron microscopy showed that compared with the control group,most of the cell walls shrank obviously and Campylobacter jejuni gathered together dryly at high doses.The ultrastructure of cells also changed significantly,and severe plasmolysis occured,some of which even became vacuoles.Finally,the mechanism of electron beam irradiation on biological molecules of Campylobacter jejuni was studied.PFGE results showed that electron beam irradiation broke the DNA strands and made bacterial DNA from large fragments to small fragments.The results of Raman spectroscopy showed that the energy emitted by electron rays destroyed the spatial conformation of bacterial nucleic acids and proteins to a certain extent.The results of biochemical experiments showed that the carbonyl concentration of the treatment group was higher than that of the control group,and there were significant differences at high doses(P<0.01).The expression of ten stress response genes of Campylobacter jejuni was detected by fluorescence quantitative PCR.The results showed that bacterial oxidative stress response genes(sodB,katA,ahpC)were significantly up-regulated at high doses(P<0.05).2.Sterilization process of Campylobacter jejuni on chicken meat surface irradiated by electron beam irradiationThe sensitivity of Campylobacter jejuni to electron beam irradiation is susceptible to environmental conditions.In order to kill Campylobacter jejuni on chicken meat more effectively,it is necessary to determine the appropriate irradiation dose combined with the specific external environment.The effects of initial bacterial quantity,pH value,water content,oxygen concentration and storage time on the germicidal efficacy of electron beam irradiation were studied.The results showed that when the initial bacterial quantity was higher,the irradiation dose needed was higher;the germicidal efficacy was worse when the pH value was 7.0,and the bactericidal rate was 98.5%;the bactericidal effect on Campylobacter jejuni was remarkable when the content of water was high(P<0.05);the germicidal efficacy was worse under the microaerobic(5%O2)environment,and the bactericidal rate was 24%.Chicken meat was stored at 4℃ for 10 days after irradiation,the survival rate of Campylobacter jejuni decreased gradually,and the number of bacteria decreased by 2.95 LogCFU.The experimental data was fitted by Origin8.0,and a series of kinetic equations were obtained.Their R2 all exceeded 0.90,which indiacted that the irradiation model was in good agreement with the actual value.According to Box-Behnken experimental design,the bactericidal process was optimized with irradiation dose and temperature as independent variables,and the survival counts of Campylobacter jejuni,chicken redness value(a*)and chicken brightness value(L*)as response values,in order to achieve the best sterilization efficacy and chicken quality.The optimal irradiation mode was established and the optimal conditions were verified.Then it was applied to sterilize clinical chicken samples.According to the experimental results and regression equations,the parameters of chicken redness,chicken brightness and the survival counts of Campylobacter jejuni were intersected.In order to minimize the adverse effects of electron beam irradiation on chicken quality,the irradiation dose and temperature were chosen as 0.3 kGy and 15℃,separately.Chicken meat simulation experiments were carried out under the optimal conditions.The results showed that electron beam irradiation can control Campylobacter jejuni on chicken meat effectively(bactericidal rate was 98%-99%)and ensure the chromaticity value of chicken meat.The results of clinical chicken samples sterilization showed that electron beam irradiation can not significantly reduce the positive rate of Campylobacter jejuni on chicken meat,but can significantly reduce the loads of Campylobacter jejuni(reduction of 2.31 Log)and total bacteria(reduction 0.92 Log)(P<0.05).3.Effect of electron beam irradiation on the quality of chicken meatThe evaluation indexes of chicken meat quality include malondialdehyde,lactic acid,pH value,tenderness,hydraulic value,volatile base nitrogen and chroma.The experimental results showed that electron beam irradiation had no significant effect on the quality of chicken meat at the optimal dose(0.3 kGy)(P>0.05).The results showed that the MDA content of chicken meat increased during storage period,and there was no significant difference between the optimal dose and control group(P>0.05).The results showed that the lactic acid content decreased gradually during storage period.Compared with the control group,2.5 kGy of irradiation significantly reduced the lactic acid content of chicken meat(P<0.05).The results showed that the pH value of chicken meat increased during storage period,and there was no significant difference between the optimal dose and control group(P>0.05).The results of tenderness test showed that the shear stress value decreased during 15 days of storage period.Compared with the control group,2.5 kGy of irradiation significantly increased the tenderness of chicken meat(P<0.05).The results showed that the hydraulic value of chicken meat increased during storage period,and there was no significant difference between the optimal dose and control group(P>0.05).The results of TVB-N value test showed that the TVB-N value increased during storage period.Compared with the control group,2.5 kGy of irradiation significantly decreased the TVB-N value of chicken meat(P<0.05).The results showed that L*value increased during storage period,and L*value of the 2.5 kGy dose group was significantly higher than that of the optimal dose group(P<0.05).Compared with the control group,a*value of the optimal dose group had no significant difference(P>0.05),and a*value of the 2.5 kGy dose group was significantly higher than that of the control group(P<0.05).The results also showed that b*value increased during storage period,and b*value of the control group was significantly higher than that of the 2.5 kGy dose group(P<0.05). |
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