| Chicken contains a variety of proteins,vitamin C,vitamin E and other nutrients,and has a high digestibility,which can be easily absorbed and used by human to enhance physical strength and strengthen the body.In addition,chicken meat is rich in phospholipids,which are important for human growth and development,and is one of the important sources of fat and phospholipids in the dietary structure of Chinese people.However,chicken meat is highly susceptible to microbial infestation,causing a decline in quality and a shortened shelf life.Moreover,human contact or consumption of chicken contaminated with bacteria(such as Escherichia coli,Salmonella,Staphylococcus aureus and Listeria monocytogenes)can easily lead to bacterial diseases,which can endanger health and even life.Traditional chicken preservation technologies(such as heat treatment,refrigeration and freezing,ultraviolet radiation and vacuum packaging)can inhibit the growth and reduce the number of microorganisms,but they are inadequate in controlling the quality of chicken.Researchers are now focusing on active food packaging preservation technology,a method to effectively maintain the quality of chicken by adding a certain amount of an active substance to the packaging material to maintain the quality and extend the shelf life of the chicken.Polyvinyl alcohol/chitosan(PVA/CS)composite film has good biocompatibility and biodegradability,but its mechanical properties and antibacterial properties are weak,and the addition of nano-fillers can greatly improve the performance of the composite film.Nanofillers with good antimicrobial properties can improve the inhibition of microorganisms in composite films,improving the quality of stored meat products by limiting the growth of microbiota and retarding the oxidation of lipids and proteins.In this paper,nickel clusters with superparamagnetic and efficient antimicrobial properties were prepared by thermal decomposition,added into PVA/CS composite film to improve the mechanical and antimicrobial properties of the film,and investigated the effect of the composite film on the preservation of cold chicken.(1)Preparation and characterization of magnetic nickel clusters.In the reducing environment of Diethylene Glycol(DEG),through the joint action of Na OH and Sodium citrate(Na Cit),Ni2+ was reduced to Ni monomers and aggregated to form clusters with superparamagnetic properties.By Fourier-transform infrared spectroscopy(FTIR),X-Ray Diffraction(XRD)and X-ray Photoelectron Spectroscopy(XPS)analysis,it was confirmed that Na OH and Na Cit were involved in the cluster formation.According to Differential scanning calorimetry(DSC)and Vibrating Sample Magnetometer(VSM)tests,it was found that the clusters had good thermal stability and superparamagnetism.Particle size analysis by particle sizer and Scanning electron microscope(SEM)showed that the cluster size was around 180 nm,which possessed large specific surface area and the basic properties of general metal nanoclusters.(2)Antibacterial properties of magnetic nickel clusters.Metal nanoclusters have a large specific surface area,which can generate a large amount of reactive oxygen species and free radicals,and can release metal ions,thus interacting with bacterial cell membranes and damaging the organisms leading to death.Escherichia coli,Salmonella,Staphylococcus aureus and Listeria monocytogenes,common spoilage bacteria of chicken meat,were used as the objects of study.The inhibition circle diameter,inhibition rate and growth curve of the bacteria treated with magnetic nickel clusters were determined,and the clusters were found to have broadspectrum inhibition,with good inhibition effect on all the studied species,and the lowest inhibition concentration for Staphylococcus aureus could be as low as 100μg/m L,and the inhibition circle diameter for Escherichia coli could reach 14.5±0.11 mm,which is moderately sensitive.Further microscopic observation of the clustertreated research strains by inverted electron microscopy,confocal laser microscopy and scanning electron microscopy revealed that clusters can attach to the bacterial cell surface,causing cell membrane damage and crumpling,collapsing and breaking the bacterial cells,thus achieving bactericidal effects.Also clusters attached to the surface of bacteria can attract magnetic clusters by an applied magnetic field and gather bacteria,thus achieving bacterial removal.(3)Preparation and characterization of magnetic nickel clusters/polyvinyl alcohol/chitosan composite films.Characterization by FTIR,XRD and SEM revealed that in the magnetic nickel cluster/polyvinyl alcohol/chitosan composite films(Ni/PVA/CS composite films),the magnetic nickel cluster physically interacts with the PVA/CS matrix,and no new chemical bonding or crystal structure formation was found.The observation of Ni/PVA/CS composite films surface and cross-section revealed that the surface roughness of the composite films increased with the increase of cluster concentration in the matrix,which led to the decrease of the fracture tensile rate and the increase of the water vapor transmission rate.However,the addition of clusters increased the tensile strength of the films by a factor of 1.20～2.33,extended the ultraviolet resistance of the films to 223 nm,and most importantly,improved the antibacterial properties of the films,with the diameter of the inhibition circle of the composite films reaching14.49±0.08 mm.(4)Application of magnetic nickel clusters/polyvinyl alcohol/chitosan composite films in chicken preservation.The Ni/PVA/CS composite films were used to preserve cold chicken meat.By observing the changes in the appearance of chicken meat,scoring the sensory evaluation,and measuring the physical(weight loss,texture,color)and chemical indicators(p H,TVB-N,TBARS and colony count),it was found that the Ni/PVA/CS composite films maintained the quality of chicken meat better during the 10-day storage period,and the physical and chemical indicators were always below the spoilage range limit.Compared with chicken meat without composite film treatment,Ni/PVA/CS composite films extend the storage period of chicken meat up to 10 days,effectively maintaining the freshness and nutritional value of chicken meat,avoiding food waste and increasing the commercial value of chicken meat.In summary,the new composite antimicrobial film prepared by incorporating magnetic nickel clusters into PVA/CS matrix can effectively inhibit the growth of chicken spoilage bacteria,improve the storage quality of chicken meat,reduce the waste of resources,and bring more commercial opportunities for chicken meat production and sales,and this Ni/PVA/CS composite film is expected to be used as a new type of food antimicrobial packaging for cold chicken preservation. |
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