| Ready-to-eat cooked meat products are nutritious,quick and convenient to consume,and are favored by consumers.However,when stored in the refrigerator for a long time,they are susceptible to contamination by Listeria monocytogenes,which can cause foodborne diseases.Therefore,it is important to find a safe and effective method to control Listeria monocytogenes in cooked meat products.Euryale ferox seed shell,as a by-product of euryale production,are often discarded or burned.In order to protect the environment and achieve efficient utilization of resources,this study extracted safe and natural active antibacterial phenolics from gorgonian shells without drug resistance,and conducted an in-depth study on the antibacterial activity and mechanism of Listeria monocytogenes.Considering the drawback that polyphenols from the Euryale ferox seed shell are not suitable for direct application,this study firstly prepared ethyl cellulose-carboxymethyl chitosan/gelatin bilayer film with hydrophobic outer layer and hydrophilic inner layer,and encapsulated polyphenols from the Euryale ferox seed shell in the inner layer of the bilayer film to impart antibacterial and antioxidant properties to the film,and finally applied the active bilayer film to the antibacterial preservation of cooked chicken and cooked beef.The main findings of this paper are as follows:（1）Analysis of the antibacterial activity and mechanism of polyphenols from the Euryale ferox seed shell against L.monocytogenesLC-MS analysis of purified polyphenols from the Euryale ferox seed shell showed that it contained 9 kinds of phenolic substances.The experiments of minimum inhibitory/bactericidal concentration,bacteriostatic zone and growth curve showed that polyphenols from the Euryale ferox seed shell could show significant inhibitory effect on L.monocytogenes at low concentrations（2 and 4 mg/m L）.The results of scanning electron microscopy,cell membrane permeability,cell wall integrity,and bacterial group motility assay showed that L.monocytogenes cell wall and cell membrane structural integrity were altered by polyphenols from the Euryale ferox seed shell,causing intracellular leakage of various ions,proteins and other substances,and affecting the activities of enzymes related to respiratory metabolism and TCA cycle.In addition,polyphenols from the Euryale ferox seed shell had an obvious inhibitory effect on the hemolytic activity of hemolysin and had an effect on the proliferation and diffusion of bacteria,which was manifested in its negative influence on the movement of bacterial community.（2）Preparation of ethyl cellulose-carboxymethyl chitosan/gelatin bilayer filmUsing ethyl cellulose as the outer material,gelatin and carboxymethyl chitosan as the inner material to prepare bilayer film,its specific characteristics are as follows:（1）the bilayer film had good light transmittance,transparency and UV barrier effect;（2）The outer water contact angle was greater than 108°,and the inner water contact angle was less than 85°,which proved that the film had the characteristics of hydrophobic outer layer and hydrophilic inner layer.（3）According to the barrier properties,mechanical properties,observed morphological characteristics and other indicators,the final determination of the preparation of the film gelatin（Gel）and carboxymethyl chitosan（CMCh）ratio was 2:1,the film had the best water vapor barrier(5.78 10-11g Pa-1s-1m-1)and oxygen barrier（20.62 meq/kg）,the highest tensile strength（TS=22.47 MPa）and elongation at break（EAB=43.71%）.（4）The SEM and AFM analyses showed that the two layers formed a mutually adherent continuous phase when the ratio of Gel to CMCh reached 2:1,which was mainly due to the hydrogen bonding interactions between CMCh and Gel and the gelatin/carboxymethyl chitosan layer and ethyl cellulose layer,making the bilayer structure denser and more stable.（3）Preparation of polyphenols from the Euryale ferox seed shell bilayer antibacterial filmStudies have shown that:（1）The addition of polyphenols from the Euryale ferox seed shell further improved the UV barrier properties,barrier properties and mechanical properties of the bilevel film.When the concentration of polyphenols from the Euryale ferox seed shell was 4 mg/m L,the peroxide value was only 15.04 meq/kg,while the TS reached 27.16 MPa.（2）After 2 months of storage,the mechanical properties and gas barrier properties have been tested to prove its good storage stability.（3）The antibacterial test of L.monocytogenes showed that the addition of polyphenols from the Euryale ferox seed shell gave the bilayer film good anti-L.monocytogenes performance.When the concentration of polyphenols from the Euryale ferox seed shell was 4 mg/m L,the antibacterial rate of the bilayer film could reached 99.46%.（4）DPPH and ABTS+free radical scavenging tests proved that the addition of polyphenols from the Euryale ferox seed shell greatly improved the antioxidant properties of the bilayer films.（6）In the bilayer film,polyphenols from the Euryale ferox seed shell in different simulated liquids all showed a tendency of increasing with a relatively large release rate in the early stage,slowing down to zero in the late stage,and reaching the maximum release.Weibull dynamic model fitting was performed on the release behavior of simulated liquid of high moisture,alcohol,acid and alcohol food.The results showed that R2of Weibull model fitting four simulated liquid was≥0.9787,which proved that this model could simulate the release of polyphenols from the Euryale ferox seed shell from the initial stage to the equilibrium.（4）Application of polyphenols from the Euryale ferox seed shell bilayer antibacterial film in cooked meat productsTaking cooked chicken and cooked beef as test subjects,the effects of polyphenols from the Euryale ferox seed shell bilayer film on microorganisms,lipid oxidation,p H,weight loss rate,chroma and texture of meat products during storage at 4℃were determined.The total number of L.monocytogenes and colonies in cooked chicken and cooked beef were significantly inhibited,and the total number of L.monocytogenes and colonies were decreased by 1.83 and 2.11 log CFU/g and 1.39 and 1.98 log CFU/g,respectively.At the same time,polyphenols from the Euryale ferox seed shell bilayer film can inhibit lipid oxidation and reduced water loss of cooked meat,and largely maintain the color and texture characteristics of cooked chicken and beef. |
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