Antibacterial Activity Of Ginger Essential Oil And Its Application In Chilled Beef Preservation

In this study,ginger essential oil（GEO）extraction process was optimized with Tongling white ginger as raw material,and GEO with high extraction rate and good quality was obtained.The antimicrobial activity and possible antimicrobial mechanism of GEO with broad spectrum were investigated.In addition,the composite film rich in GEO was prepared,and the preservatory effect of the composite film was studied for chilled beef preservation.The results of this paper can provide a theoretical basis for the application of plant EOs in food preservation.The main research results are presented as follows:Firstly,the optimal extraction conditions and the main active components of GEO were determined by supercritical CO₂.A series of pretreated ginger powder was used as raw material and the extraction rate was used as the index to optimize the process by response surface test.The optimal extraction conditions were as follows:extraction temperature was 42°C,extraction pressure was 312 bar,CO₂ flow rate was 1.6 L/min,and extraction time was 36 min.Under these conditions,the extraction yield of GEO was4.543%.GC-MS analysis showed that the main components of GEO were Zingiberene,α-Curcumene and Zingiberone,and the contents were 37.549%,10.221%,and 6.591%,respectively.Secondly,the antibacterial activity and possible antibacterial mechanism of GEO broad spectrum were investigated.The results showed the diameters of inhibition zone of16 mg/m L GEO against the four tested strains which were all greater than 10 mm.The minimum inhibitory concentration（MIC）and minimum bactericidal concentration（MBC）for E.coli were the largest,which were 2 mg/m L and 4 mg/m L respectively.The membrane potential,protein concentration,and nucleic acid content of E.coli and S.aureus were decreased after treated with GEO with given MIC and MBC.The q PCR results showed that the genes associated with cell membrane protein synthesis（PBP,mur B）,energy metabolism（ATPase,ALpase,β-GAL）and downstream genes associated with TCA cycle path（OGDH,DLST,DLD）,and DNA metabolism related genes（Rec F,Rec N,Hol A）were significantly down-regulated.However,the expression levels of some genes encoding heat shock proteins（clp A,clp B,Gro E,Grp E,Ibp A,hsl O）and TCA cycling-related upstream genes（CS,ICDH）were significantly up-regulated,which further supported the antibacterial mechanism of GEO at the molecular level.Finally,the composite films containing different proportions of GEO,Chitosan（Ch）and Montmorillonite（MMT）were prepared and characterized,and the preservatory effect of these composite films on chilled beef was evaluated.Fourier transform infrared spectroscopy（FT-IR）showed that there were a series of strong interactions between the components.The infiltration of GEO could reduce the tension resistance of the film,and increase the elongation at break and water vapor permeability.The migration of phenols in the film began to increase exponentially and reached equilibrium at 48 h.In the process of preservation of the composite film,the groups of Ch+0.5%GEO and Ch+MMT+0.5%GEO effectively delayed the rise of p H value,hue angle value and moisture value of chilled beef with time,but also effectively slowed down the fat oxidation of chilled beef and the growth of surface microorganisms,maintained the quality of chilled beef,and ultimately extended the shelf life.