Development On Intelligent Packaging Film For The Integration Of Pork Preservation Sensing And Controlled Release

70-80%of pork products in China are raw meat,which guarantees the quality and safety of raw meat is a practical challenge.Intelligent packaging films can monitor meat freshness and extend its shelf life that become hot topics at home and abroad.In this study,after the linkage of sensing and controlled release,the meat quality is perceived through the visible color changes of the packaging film.Then the stimulation conditions of controlled release can be triggered in time to realize the on-demand release of active ingredients.It can successfully extend the shelf life of meat products.Firstly,in response to the low stability and sensitivity of anthocyanin sensing packaging films,the hydrophobic bi-layer film and a hydrophobic composite nanofiber film were developed,respectively.Secondly,in order to solve the asynchronous problem between release law of the active ingredients and the demand of food preservation,the antibacterial preservation films with sustained release,external environment and internal environment controlled release were prepared,respectively.Finally,the intelligent sensing and controlled release packaging film of active ingredients can be combined.With meat freshness as the sensing function and controlled release packaging as the execution behavior,an integrated intelligent packaging system with"Sensing"and"Control"function was prepared to achieve pork preservation.The main research is as follows:（1）Preparation of a bi-layer self-sensing packaging film with high humidity-resistance for monitoring pork freshness.The existing hydrophilic anthocyanin indicators easily diffuse from the solid matrix onto the surface in high humidity environment,resulting in instability and indicator malfunction.This study developed a breathable and waterproof bi-layer intelligent sensing film by incorporating a hydrophobic outer layer.The polyvinylidene fluoride（PVDF）paper was used as the hydrophobic layer,while polyvinyl alcohol/sodium alginate and roselle anthocyanin were used as the sensing layer.The physical properties,microstructure,and color stability of the hydrophobic bi-layer intelligent sensing film were investigated with a focus on its hydrophobic properties and water vapor permeability（WVP）.The results demonstrated an increase in the water contact angle（WCA）of the prepared hydrophobic bi-layer sensing film from 56.09°to 108.85°,the WVP value was 1.42×10^-4 g/（m·s·pa）and the color response S_RGB was 22.63%.Therefore,the developed bi-layer intelligent sensing film exhibits high resistance of humidity.Finally,it was used to monitor the pork freshness with obvious color changes from red to green.（2）Preparation of an integrated composite nanofiber film with high sensitivity for pork freshness sensing and preservation.To address the issues of the reduced sensitivity from the introduction of a hydrophobic outer layer and the inability to extend the meat shelf life,this study prepared an integrated composite nanofiber film by electrospinning technology with high loading rate and large specific surface area for pork freshness sensing and preservation.PVDF polymer particles were firstly used as the film-forming material for food packaging,water-soluble roselle anthocyanin was chosen as the sensing material and alcohol-soluble cinnamon essential oil（CEO）which served as the active ingredient.The microstructure,Fourier Transform Infrared Spectrometer（FTIR）and hydrophobicity of the nanofiber film were investigated,with particular attention on its stability in pH buffer solutions and antibacterial properties.The results showed that the integrity of prepared nanofiber film was maintained in different pH solutions.The WVP value was 2.63×10^-7g/（m·s·pa）and its color response of S_RGB value increased to25.68%.The prepared nanofiber film had good antibacterial properties to effectively extend the shelf life of pork for two days.It was used to monitor of pork freshness with visual color changes from pink to light green.Therefore,achieving an integrated composite nanofiber film for pork freshness sensing and preservation on the basis of considering the stability and response sensitivity under high humidity environment.Finally,a freshness comparison indication card was created,establishing correlation between the color of sensing film and meat quality,broadening its potential practical application in meat packaging.（3）Preparation of a sustained-release packaging film of active ingredients for pork preservation based on freshness self-sensing.To address the issues of the low antibacterial efficiency and poor preservation effect due to the high essential oil volatilization of,an active sustained-release encapsulated ingredient was formulated usingβ-cyclodextrin（β-CD）as the wall material and CEO as the core material.The encapsulated process was prepared by using a saturation solution method.The optimum parameters were chosen by using a single-factor experiment:the mass ratio of CEO toβ-CD was 1:8,the encapsulation time was 3 h,and the encapsulation temperature was55℃.Then the sustained-release antibacterial nanofiber film was prepared by using PVDF polymer as the film-forming material andβ-CD@CEO as the active indigent by uniaxial electrospinning technique.The microstructure,mechanical and hydrophobic properties of the sustained-release nanofiber films with different concentrations of encapsulated materials were investigated.The release behavior of CEO in the nanofiber film was further discussed.The results showed that at a 2%concentration of encapsulated material,the inhibition zone against E.coli and S.aurous was 17.1 mm and 16.7 mm,respectively.The results of cytotoxicology showed that the cell survival rate was more than 80%,which met the first-level biosafety standards.Therefore,sustained-release packaging film can be applied for pork preservation and effectively extended the shelf life of pork for 2 days at 4℃.Finally,combined with the freshness comparison card,the preservation process of the sustained-release packaging film can be visualized.（4）Preparation of a photodynamic-controlled release packaging film of active ingredients for pork preservation based on freshness self-sensing.In order to address the problem that the uncontrolled release of active ingredients in intelligent films,the ZIF-8 metal-organic framework was synthesized and loaded with the photosensitizer Rose Bengal（ZIF-8@RB）as the photodynamic sterilization ingredient.The photodynamic-controlled release packaging film was produced using PVDF polymer as the film-forming matrix through uniaxial electrospinning technique.Firstly,the microstructure,particle size,excitation wavelength,and ¹O₂content of ZIF-8@RB were studied.Secondly,the microstructure,mechanical properties and hydrophobic properties of the photodynamic-controlled release packaging film were investigated.Then,the photodynamic sterilization effect of the packaging film was emphatically explored and its cytotoxicity was discussed.The results showed that the particle size of the synthesized photosensitizer ZIF-8@RB was about 232.80 nm and（37）_（35）was 0.403.The survival rate against E.coli was 0.83%and that of S.aurous was 0.45%.Finally,it was used for pork preservation.Combined with the freshness comparison card,the photodynamic sterilization condition can be triggered by promptly sensing the pork freshness,thereby effectively extending the storage shelf life by 3 days at 4℃.Therefore,the preservation process of photodynamic sterilization can be visualized.（5）Preparation of a pH self-controlled release packaging film of active ingredients for pork preservation based on freshness self-sensing.To address the problem that poor antibacterial effect was caused by the inconsistent release law of active ingredients with the requirements of meat preservation,a pH-controlled release film was prepared to achieve self-controlled release of active ingredients to improve the preservation effect of the film.The pH self-controlled release packaging film was developed using CEO as the active ingredient and L100 with trace amounts of citrate,as the polymer matrix by coaxial electrospinning technology.Firstly,the core-shell structure of the pH-controlled release nanofiber film was confirmed by microstructure and then its physical properties were characterized.The release kinetics mechanism in different pH solutions and bactericidal effect were further emphasized.The results showed that the prepared pH-controlled release nanofiber film had a high specific surface area（7.22 m²/g）and WCA was 121.45°.With the increase of pH,the release rate of CEO increased from68.9%to 98.2%,and the release kinetics model revealed that the mechanism on relaxation erosion of the polymer at high pH and fick diffusion at low pH.Finally,pH-controlled release nanofiber film was used for pork preservation.As the pork storage time increased,the pH of the packaging environment changed,causing the macroscopic behavior changes of the polymer matrix.Then the release channel of the active ingredients self-activated,successfully extending the shelf life of pork to 4 days at 4℃.Combined with the freshness comparison card,the automatic linkage between pH-controlled release preservation process and intelligent sensing of pork freshness can be realized and visualized.The preparation of the pork sensing-controlled integrated intelligent packaging film in this study can also be used for beef,fish and other foods with high protein content,laying a foundation for further industrial production of related intelligent packaging film.