Study On Bactericidal Mechanism Of Plasma Activated Water Against Shewanella Putrefaciens And Preservation Of Carp Fillets

As a new sanitizer,plasma activated water(PAW)has been widely used in the sterilization and preservation of fruits and vegetables,livestock,poultry meat and seafood,but it is seldom used in fresh water products,and the sterilization mechanism on spoilage bacteria has not been thoroughly studied.In this work,an atmospheric pressure plasma jet device was used to prepare PAW by discharging on stertile deionized water(SDW)surface for 60,90,120 and 150 s,denoted as PAW60,PAW90,PAW120 and PAW150,respectively.In this study,the inactivation effect and mechanism of PAW on Shewanella putrefaciens and the effect on the quality of carp fillets were investigated.In addition,the synergistic effects of PAW combined with chitosan-oregano essential oil coating on preservation of carp fillets were studied.The main results are as follows:(1)The changes in cell morphology,cell membrane permeability and cell content leakage were measured to explore the inactivation mechanism of PAW on Shewanella putrefaciens.The results showed that the number of Shewanella putrefaciens was significantly decreased(P<0.05).After being treated by PAW120 for 1.5,3.0,4.5 and 6.0min,the rupture and crumpling of cell morphology was observed,the permeability of the inner and outer membranes was increased.Moreover,the leakage of intracellular nucleic acid,protein,macromolecules,and the electrical conductivity increased significantly(P<0.05).The results of Fourier transform infrared showed that the lipid and protein structures of bacterial cells were changed after PAW120 treatment.(2)The effect of PAW-induced inactivation of Shewanella putrefaciens cells on carp filets and the quality of carp fillets were investigated.The results showed that the number of Shewanella putrefaciens cells was significantly decreased(P<0.05)after being treated by PAW60,PAW90,and PAW120 for 3 min compared with control.Furthermore,a maximum reduction of 1.03 log₁₀ CFU/g for Shewanella putrefaciens cells was observed after exposure to PAW120 for 6 min compared with the control.Compared with SDW,PAW120 caused no significant(P>0.05)changes in sensory properties and texture attributes of carp fillets.However,Compared with SDW-treated samples,the L^*value of PAW120-treated carp fillets was increased and the a^*value was decreased after PAW120 treatment,whereas there was no significant(P>0.05)difference in the b^*value.There were no significant(P>0.05)changes on the lipid oxidation level and a decrease in the p H value of the carp fillets after being treated by PAW120 for 1.5,3.0 and 4.5 min.(3)The synergistic effects of PAW combined with chitosan-oregano essential oil coating on quality changes of carp fillets were studied during the chilled storage.The total number of colonies in SDW,PAW,CS-OEO and PAW+CS-OEO groups increased gradually during the chilled storage.However,compared with the other groups,the total number of colonies was significant decreased(P<0.05)after PAW+CS-OEO treatment and did not exceed the national standard(6 log₁₀ CFU/g)at the 10th day during chilled storage.Morever,compared with the other groups,the p H,thiobarbituric acid,color,texture,and total volatile basic nitrogen of carp fillets were better after being treated by PAW+CS-OEO.The results of K value showed that the deterioration of quality of carp fillets was effectively inhibited after PAW+CS-OEO treatment during chilled storage.Compared with the other groups,the results of sensory evaluation showed that there were good sensory score on the color,appearance,odor,and texture of carp fillets after PAW+CS-OEO treatment during chilled storage.