Preparation Of Gliadin-encapsulated Silver Nanoparticles By Green Reduction Of Carnosic Acid And Its Antibacterial Properties

Silver nanoparticles(AgNPs)has the characteristics of good antibacterial property,broad spectrum,safety,and no drug resistance,and can be used as a long-acting antibacterial agent.However,silver nanoparticles is easily agglomerated and oxidized during preparation or application,losing its proper properties and functions,thus limiting its application in food packaging systems.In this thesis,the green synthesis of silver nanoparticleswas studied.The interaction between silver nanoparticles and gliadin was used to construct stable wheat gliadin/AgNPs composite particles.The system studied its particle stability,biocompatibility,antibacterial properties and its application in packaging materials.The main research conclusions are as follows:1.Using liquid phase reduction technology,the spherical silver nanoparticles with an average particle size of 23±6nm were synthesized by using carnosic acid as a reducing agent,and the structural characteristics,antibacterial property and storage stability of the silver nanoparticles were studied.Studies have shown that carnosic acid can be reduced by the action of hydroxyl and carboxylate groups to obtain silver nanoparticles.Antibacterial experiments showed that the silver nanoparticles had a significant antibacterial effect compared to the single component(silver nitrate,carnosic acid),and the inhibition zone diameters were 16.67mm(S.aureus)and 7.33mm(E.coli),respectively,showing synergistic antibacterial activity effect.However,the silver nanoparticles have poor stability,and they tend to aggregate when placed for a long time,which affects the antibacterial property of the nanoparticles.2.Using the amphiphilicity of gliadin,gliadin/AgNPs with a particle size of 26±5nm were constructed for the first time by self-assembly.The structural characteristics,cytotoxicity,antibacterial property and storage stability of gliadin/AgNPs were systematically studied.Studies have shown that gliadin/AgNPs have better long-term storage stability(>3 months)than AgNPs.The stabilizing mechanism includes the steric hindrance effect between the particles and the repulsion effect caused by the same surface charge of the shell.In addition,when the silver concentration is 13?g/mL,the cell viability is still 90%,indicating that the wheat gliadin shell layer can improve the cytocompatibilityof gliadin/AgNPs,and has no significant effect on the antibacterial property.The effect is remarkable.It can be used as a good antibacterial agent in the field of food packaging.3.The biocompatible antibacterial composite film with stable gliadin/AgNPs composite particles was prepared by casting method.The structural characteristics of the antibacterial composite film,the cumulative amount of nanosilver,biocompatibility and antibacterial property were studied.Studies have shown that the glaidin/AgNPs composite film prepared by casting has good transparency.The results of SEM and EDS showed that the stabilizing effect of gliadin on gliadin/AgNPs prevented the AgNPs agglomeration during the film formation,and it showed a uniform distribution in the film.The nano-silver in the AgNPs composite film exhibits a clear agglomeration and uneven distribution.The gliadin/AgNPs embedded in the chitosan film achieve the purpose of sustained release,and can be sustainedly released,and the cumulative silver release amount in 15 days is 511 ppb;At the same time,the composite membrane has obvious antibacterial effect,and its good biocompatibility provides a practical solution for food packaging.