Synergistic Antibacterial Effects Of ?-polylysine Hydrochloride Combined With Phenolic Acids And Their Application In Preservation Of Sea Bass

?-polylysine hydrochloride(?-p L)is a natural preservative with strong antibacterial activities and weak antioxidant activities.Phenolic acid is a kind of natural antibacterial agents and antioxidants from plants,which have been reported to be used in many fields of food processing and preservation.In this study,the inhibitory activities of gallic acid(GA),protocatechuic acid(PA)and chlorogenic acid(CA)on Shewanella putrefaciens in aquatic products were compared,and then synergistic antibacterial effect and mechanism of phenolic acids and ?-p L were revealed.On this basis,a composite preservative was developed and its effect on the quality of refrigerated sea bass was investigated,which provides a scientific basis for the application of ?-polylysine hydrochloride and phenolic acid in the preservation of aquatic products.The main results are as follows:1.Antibacterial activities of phenolic acids against S.putrefaciens and synergistic antibacterial effect of phenolic acids and ?-p L were evaluated.The results showed that the inhibition zone diameters of the three phenolic acids all increased with increase of the concentration,and antibacterial activities of the three phenolic acids against S.putrefaciens from high to low were GA,PA and CA.Minimal inhibitory concentration(MIC)and minimal bactericidal concentration(MBC)of GA against S.putrefaciens were 1.25 mg/m L and 2.5 mg/m L,respectively.Fractional inhibitory concentration index(FICI)of ?-p L and phenolic acids were all less than 0.5,indicating that ?-p L and phenolic acids possess a good synergistic antibacterial effect.The results of growth curve and time-killed bactericidal curve further demonstrated the synergistic antibacterial activities of GA and?-p L.2.Scanning electron microscopy,flow cytometry,cell membrane integrity and permeability analysis were conducted to further reveal the synergistic antibacterial mechanism of ?-p L and GA.The results showed that ?-p L and GA at concentration below MIC could cause a small amount of cell apoptosis and necrosis,but did not cause changes in morphology,cell membrane integrity and permeability of most bacteria.The combination of ?-p L and GA at a low concentration can significantly destroy the integrity of S.putrefaciens cell membrane and increase the permeability of cell membrane,which cause the leakage of nucleic acid,protein and other components in bacterial cells,and increase the apoptosis rate,destroy the bacterial morphology and ultimately inhibit the growth of S.putrefaciens.Therefore,the combined use of ?-p L and GA has a synergistic effect on the inhibition of S.putrefaciens from aquatic products and can significantly reduce the effective dosage.3.Pullulan and carboxymethyl cellulose sodium composite coating combined with GA,?-p L,and GA-?-p L were used for preservation of sea bass fillets at 4? storage for 20 days.Sensory evaluation,total viable counts(TVC),water holding capacity(WHC),low field nuclear magnetic resonance analysis,p H value,total volatile base nitrogen(TVB-N),thiobarbituric acid(TBA),texture,and electronic nose were performed to evaluate effects of composite coating and ?-p L combined with GA on the quality of sea bass.The results show that antibacterial agent significantly enhanced the preservation effect of composite coating.Compared with other treatment,The coating-GA-?-p L significant reduces TVC,p H value,WHC and TVB-N,and TBA of fillets,indicating that ?-p L combined with GA possess good synergistic effects on inhibition of microorganism and delaying of fat oxidation,protein degradation and water loss which suggest a potential application in fish preservation.