Study On Green Synthesis Of Silver Nanoparticles And Its Antibacterial And Preservation Properties

Because of their chemical stability,thermal stability,and antibacterial activity,silver nanoparticles(AgNPs)have a wide range of uses in biomedicine,food preservation,and other industries.The synthesis of AgNPs,particularly green synthesis and antibacterial applications,has gotten a lot of attention in recent years.This thesis investigated the green synthesis,antibacterial activity,and antibacterial mechanism of AgNPs,as well as the application of AgNPs composite film in the postharvest preservation of strawberries.The results of the study provides theoretical foundation and technical support for using AgNPs as antibacterial and preservatives in food industry.The following were the main finding:(1)Synthesis of AgNPs using banana flower extract and its characterization.UV-Vis was used to identify the best reaction conditions,which were as follows:the concentration of Ag NO₃ was 4 m M,the reaction time was 120 minutes,and the reaction temperature was 90°C.The solution was reddish-brown,and the synthesized AgNPs displayed a distinctive absorption peak at?=409 nm.The functional groups in the banana flower extract were involved in the reduction and stabilization of AgNPs,according to TEM,XRD,FT-IR,and TGA characterization,and the synthesized AgNPs had a spherical shape and a particle size of around 11.86±3.88 nm,with good dispersion and thermal stability.(2)Antibacterial activity and antibacterial mechanism of AgNPs.By 96-well plate micro assay and growth curve method,the minimum inhibitory concentration(MIC)and minimum bactericidal concentration(MBC)of AgNPs against S.aureus were 32?g/m L,while the MIC and MBC against E.coli were 16?g/m L.The difference in AgNPs resistance to the two bacteria was mainly due to the different cell wall structure of the two bacteria.On the one hand,the antibacterial properties of AgNPs from the destruction of the cell membrane,which causes a change in bacterial morphology,which leads to the leakage of contents and,eventually,the death of the bacteria;on the other hand,it stem from the generation of reactive oxygen species(ROS),which can be seen under a fluorescence microscope.The production of ROS increased dramatically in bacteria treated with AgNPs,causing membrane and biomolecular disruption,while the antioxidant N-acetyl-L-cysteine (NAC)repaired the damage caused by AgNPs to bacteria,indicating that the production of ROS is one of the essential antibacterial mechanism of AgNPs.At the same time,AgNPs can cause the inactivation of important enzyme(bacterial respiratory chain dehydrogenase).(3)Preparation of PVA/CS-AgNPs film and its application in strawberry preservation.The AgNPs were successfully incorporated into the PVA/CS substrate,according to the film appearance color and FT-IR results,and the addition of AgNPs improved the UV blocking properties,tensile strength,elongation at break,and oxidation resistance of the PVA/CS films,while reducing the film thickness and water vapor transmission rate.In terms of preservation,the addition of AgNPs improved the preservation effect of PVA/CS film on strawberries.The rotting rate of strawberries treated with PVA/CS and PVA/CS-AgNPs films was significantly reduced when compared to the blank group and PE film group,with PVA/CS-AgNPs films having a stronger effect than PVA/CS films,which was due to the outstanding antibacterial activities of AgNPs.Both composite films can assist preserve the appearance quality of strawberries while also delaying changes in hardness,soluble solids,p H,and V_C value during the shelf-life.However,PE film outperforms PVA/CS and PVA/CS-AgNPs films in terms of water retention.