Preparation And Study On Controlled Release Property Of Antibacterial Packaging Film Based On The System Of Cinnamaldehyde/poly(Vinyl Alcohol)

Biodegradable antibacterial packaging materials can not only be used as an important means of food preservation,but also can alleviate the environmental problems caused by the extensive use of plastic to some extent.In addition,with the improvement of people's awareness of food safety,natural antibacterial agent has caused widespread concern in the food industry.It is an innovation in the current food industry to prepare antibacterial packaging material by adding natural antibacterial agent to the degradable materials.In this paper,Poly?vinyl alcohol??PVA?-based antimicrobial packaging films were prepared by different ways using cinnamaldehyde?CIN?as antibacterial agent.The mechanical properties,water vapor permeability,transparency,as well as antibacterial activity of the prepared films were investigated.The correlation between film's structure and the release of antibacterial agents was explored.The main results and conclusion in the paper were summarized as follows:?1?Preparation and characterization of blend and cross-linked PVA-CIN antibacterial films.PVA-CIN blend and cross-linked films incorporated with different concentrations of CIN were prepared.The results from FTIR and¹H-NMR analysis revealed that the aldol condensation reaction between CIN and PVA occurred under acidic conditions.The SEM observation showed that there were many discontinuous pores or cavities in the cross-section of the blend film,while the cross-linked film was smooth,continuous and dense.The change of microstructure gave the cross-linked film higher degree of transparency.The tensile strength?TS?of the cross-linked films was higher than that of the blend film.And the elongation at break?EB?value varied with the amount of CIN added.When the amount of CIN added was 0.5%and 1%,the EB value of the film was higher than that of the mixed film and when the amount of CIN added was 2%,EB value was lower than that of the blend film.With increasing of CIN concentration,the water vapor permeability?WVP?of blend film increased,while WVP of cross-linked films declined.At the same CIN concentration level,the water vapor barrier of the cross-linked films was higher than that of the blend films.Antibacterial activities of each film-forming dispersion and antimicrobial films against Escherichia coli?E.coli?and Staphylococcus aureus?S.aureus?were analyzed.The results showed that the antibacterial activities of cross-linked film-forming dispersion or films were less slightly than that of blend film-forming dispersion or films.The results of CIN retained in films showed that the retention of CIN in the cross-linked film decreased,which was in agreement with the result from ¹H-NMR analysis,namely that part of the CIN was involved in the cross-linking reaction and formed covalent bond with PVA molecules.Results also showed that the release of CIN in cross-linked films was largely dependent on environmental conditions,and higher humidity can promote rapid release of CIN from film.Based on the higher transparency and vapor barrier property of the cross-linked film,as well as its controlled release of CIN in lipid simulation,chilled pork was packaged with it to prolong the shelf-life of chilled pork.?2?Preparation and characterization of CIN microcapsule films.The microcapsule particles were prepared using EC as the wall material and CIN as the core material by the anti-solvent method.In the blend system of ethanol and CIN,with water was slowly added to the solution of ethanol and CIN,the largely hydrophobic CIN molecules would precipitate or form into small crystals and the EC chains slowly self-assemble themselves around the crystals with its hydrophilic group?-OH?facing the aqueous phase and its hydrophobic group?C₂H₅O-?accumulating inwards to form a hydrophobic interior.By this self-assembly method,hydrophobic internal cavity was formed and the CIN was then encapsulated therein.The FTIR and thermal analysis showed that CIN was successfully encapsulated in the EC wall material.The microcapsules were observed to be spherical by SEM.The encapsulation efficiency of CIN increased as the microcapsule wall material increased.The PVA-CIN-EC microcapsule antibacterial films were prepared by mixing the microcapsule suspension with different EC content and the PVA aqueous solution.All of the prepared film showed high water vapor barrier property.When the EC ratio was 10%,the WVP of microcapsule film was lower than that of the pure PVA film by 3 orders of magnitude,and the water vapor barrier property of the microcapsule film continued to increase as the proportion of EC in the film increased,while the mechanical properties and transparency of the film decreased.The EC content in microcapsules was an important factor affecting the antibacterial properties of films.The results of the inhibition zone showed that when the EC content in the film was 4%,the inhibition zone diameter of the film against S.aureus was 7.02mm,but no inhibition zone was observed around other microcapsules films.The release studies found that the release rate of CIN in microcapsule films was less than 30%,with almost no release,but could be slowly released in a relatively high humidity environment.?3?Preparation and characterization of Pickering emulsion film.SiO₂ was modified with vinyltrimethoxysilane?VTMOS?to prepare modified silica?m-SiO₂?with a water contact angle?WCA?of 85°.Adding CIN into different concentrations of m-SiO₂ aqueous dispersion,a stable Pickering emulsion can be formed when the m-SiO₂ concentration was 3%.Pickering emulsion films?PVA-CIN-PK?were prepared by mixing Pickering emulsion with PVA aqueous solution.The core-shell structure on the surface of the prepared films was observed by CLSM.The CIN retention of Pickering emulsion films were higher than that of PVA-CIN blend films,cross-linked films and microcapsule films.The amount of the Pickering emulsion had an influence on the dispersion and size of the film-forming dispersion.As the addition of the Pickering emulsion increased,the particle size increased and dispersibility decreased.Pickering emulsion droplets partially agglomerated in the film-forming dispersion when the amount of Pickering emulsion was increased to 10%.AFM revealed that as the amount of Pickering emulsion increased,the roughness of the film increased and thus transparency decreased.The addition of the Pickering emulsion also affected the color,TS,and EB values of the films.With increase of the addition of Pickering emulsion,the color of the film gradually turned yellow,and the TS value and EB value of the film decreased gradually.Compared with the pure PVA film,the WVP of films decreased when the adding amount of Pickering emulsion was 2.5%and 5%,while it increased when the adding amount of 10%.The Pickering emulsion film with a sustained release under high humidity was established.?4?Preparation and characterization of PVA-CIN-Ag ternary complex film.Silver nanoparticles?Ag-NPs?were in-situ generated using PVA-CIN microemulsion as the reduction and stabilization system.The PVA-CIN microemulsion also served as the basic component of the ternary composite film.The organic and inorganic antimicrobial agents were fully mixed in the film by this method.The UV-vis,XRD and TEM analysis showed that the particle size and dispersity of Ag-NPs depended on CIN concentrations.Ag-NPs with uniform particle size and good dispersibility could be prepared when the concentration of CIN was 0.5%.Plasmon resonance absorption peaks of the obtained nanosilver still appeared near 434 nm after 3 months storage.There were no red-shift or blue-shift phenomenon of prepared silver colloid indicated that Ag-NPs did not agglomerate after long-term storage and had good dispersion stability.Compared with pure PVA,the TS and EB value of the ternary composite films increased,while the water vapor barrier property was decreased.Meanwhile,with the proportion of nano-silver sol increased,the color of the film gradually deepened and the transparency declined.The release of silver in the composite film was slow,indicating that the preparation of film with PVA as a carrier of silver can achieve the effect of solidifying nano-silver and slowly releasing it.The results of antibacterial test showed that the combination of inorganic and organic antibacterial agents made the ternary composite film having a strong antibacterial effect,which was better than that of the film using CIN alone as antibacterial agent.In conclusion,the results of this study showed that the different addition methods of CIN played a key role in the functional modification of PVA based films and thus had an influence on the properties of films related to food packaging.In addition,the nano-silver particles were prepared by means of CIN microemulsion and then introduced it into the ternary composite films to make the organic and inorganic antibacterial agents mix well,which further enhanced antibacterial properties of films.The preparation of antibacterial films in this study provides a reference for the functional modification of other plant essential oils in different film forming matrix.