Effect Of Pulsed Electric Field On Pathogenic Bacteria Of Sterilization And Quality In Fresh-cut Apple

With the increasing living standard,there is a growing demand of fresh-cut products.Compared with the full raw materials,The protection structure of fresh-cut products was damaged and more susceptible to be infected by pathogenic bacteria,including E.coli and salmonella enteritidis,which may lead to a foodborne disease outbreaks.In this study use fresh-cut apples as the object,the effect of Pulsed Electric Fields(PEF)on the bactericidal effect and quality of pathogens was discussed.The sterilization effeciency of pulsed electric field on E.coli and salmonella enteritidisattached to the fresh-cut apple by using the different pulsed intensity,treating time,pulsed duty ratio,pulsed frequency,and the growth of the two bacteria was studied after treated by PEF and 40 mL/L H2O2,respectively.The effects of pulsed electric field treatment on the growth curve of Escherichia coli and Salmonella enteritidis at room temperature(25 °C)were studied by microbial dynamics model.Meanwhile the influence of PEF orthogonal test on the quality and sensory quality of fresh-cut applewas also detected.The main contents of this study were:1.Different PEF treatment conditions show that:pulsed intensity,treating time,pulsed duty ratio had a positive correlation with the amount reduction of E.coli and Salmonella enteritidis,and pulsed frequency had a negative correlation with that.The electric field intensity increased from 5 to 45 kV/cm,the reduction of E.coli increased from 0.69 to 1.82 log(CFU/g),and the reduction of Salmonella enteritidis increased from 0.65 to 2.30 log(CFU/g).With the increase of treatment time,the reduction of Escherichia coli increased from 0.0 to 1.49 log(CFU/g),and the reduction of Salmonella enteritidis increased from 0.0 to 1.93 log(CFU/g).The pulse duty cycle increased from 0%to 48.8%,the reduction of E.coli increased from 0.91 to 1.461og(CFU/g),and the reduction of Salmonella enteritidisincreased from 0.82 to 1.99 log(CFU/g).However,there was no significant difference in the reduction of Escherichia coli and Salmonella enteritidis(p?0.05)in the range of 10.3?30.5 kHz.During the storage of fresh-cut apples,the average amount of bacteria in different treatment groups increased by 1.23 log(CFU/g).2.The microbial changes in PEF treatment and 40 mL/L H2O2 solution for 96 h were compared.he results showed that:PEF had a satisfactory sterilization efficiency,the results showed that the E.coli and Salmonella enteritidis sterilizing rate achieved 99.40%and 99.77%,respectively,while the control treating group only achieved 85.57%and 77.75%of the two bacteria.3.Modified gompertz monitor the growth of the E.coli and Salmonella,the results showed that the coefficient of determination R2 were all greater than 0.9841,root mean square error(RMSE)were all less than 0.2123,and the fitted models reached the significant level of p?0.01.When increasing the intensity of pulsed electric field,the lag phase ? were increased from 4.5 3h to 6.23 h of E.coli and 1.91 h to 6.05 h of Salmonella enteritidis,and the initial cfu(N0)of E.coliand Salmonella enteritidiswere decreased from 4.78 to 3.67 log(CFU/g)and 4.17 to 2.61 log(CFU/g),respectively.When increasing the treating time,the lag phase X were increased from 3.38h to 6.57 h of E.coli and 1.64 h to 5.11h of Salmonella enteritidis,and the initial cfu(N0)of E.coliand Salmonella enteritidiswere decreased from 5.40 to 3.93 log(CFU/g)and 4.82 to 2.91 log(CFU/g),respectively.The dynamic model of death was established through Hulsheger ? and ? model,when treated by different pulsed electric field and treating time.The results showed that the coefficient of determination R2 were all greater than 0.9915,root mean square error(RMSE)were all less than 0.0054,and the fitted models reached the significant level of p<0.01.With the increase of electric field intensity and the treating time,initial microbial survival rate declined sharply but slowed down later.The Hulsheger model.fitting parameters of E.coli andSalmonella enteritidisshowed thatbE was 0.0632 and 0.0829,Ec was-18.5508 and-13.0400,bt was 0.9728 and 1.0271,tc was 0.9613 and 1.0072,respectively,and the bE and bt value of salmonella enteritidis were lager than E.coliO157:H7,which means that Salmonella enteritidis is more sensitive to PEF treatment thanE.coli.4.The influence of the quality of fresh cut apple(the color difference(whiteness),hardness,titratable acid,TSS,Vc,respiration intensity and PPO activity and sensory)was analyzed.The results indicated that pulsed electric field had a significant germicidal efficacy of E.coliand Salmonella enteritidis attached to fresh-cut apple,and had a few influence on the sensory quality and physical quality of fresh-cut apple during storage than 40 mL/L H2O2 treatment.