Investigation Of Multifunctional Food Packaging Film Via Loading Graphene Oxide Onto The Procyanidins-Grafted-Chitosan Substrate

Traditional food packaging materials are mainly polyethylene film.In the process of preparation,the main raw materials of traditional polyethylene film are non-renewable petroleum-based resources that leads to its production and processing vulnerable to the impact of energy shortage.In the process of using,polyethylene film are prone to aging and cracking and release harmful substances affecting people's health.In the process of recycling,petroleum-based films are difficult to degrade and easy to cause "white pollution",which harms environmental health.In addition,the function of traditional materials are relatively limited and has no antibacterial property.Food processing technology by means of high temperature sterilization and low temperature storage will cause the loss of food nutrients and easily increase the consumption of resources,which is not conducive to food preservation and prolong the shelf-life.Therefore,it is very important to produce a kind of green and environmentally friendly functional packaging material that can replace traditional polyethylene film.Chitosan,as the only alkaline polysaccharide existed in nature,has good film-forming performance,antibacterial properties,antioxidant properties and biocompatibility.As a consequence,the preparation of packaging materials with chitosan as a natural biodegradable antibacterial material,conformed to the strategic requirements of sustainable development and the environmental and resource crisis could be solved.In this paper,procyanidins were grafted to chitosan in the TEMPO-laccase catalytic oxidation system,and then procyanidin grafted chitosan-loaded graphene oxide functional materials were prepared.The high antioxidant activity and special pH response of procyanidins and the excellent barrier property of GO can greatly improve the performance of chitosan based film,broaden its application field,and play a role in sterilization and prolonging food storage life.The main research results are as follows:In this paper,chitosan-procyanidins composite film(C-CS-PC)were prepared by solution casting method.The effects of different content of procyanidins on the mechanical properties,thermal stability,oxidation resistance,bacteriostatic properties,barrier properties and pH response properties of C-CS-PC film were studied.The results showed that C-CS-PC film obtained the best comprehensive performance when the mass ratio of chitosan to procyanidins was 40:3.The tensile strength reached 89.4 Mpa and increased by 29.9%.The water vapor permeability and oxygen permeability were 728.68g·m-2·d-1 and 1011cm3·m-2·d-1·bar-1,respectively,which increased by 28.04%and 40.84%.The antibacterial properties of C-CS-PC film on Escherichia coli and Aspergillus niger were significantly improved followed by Staphylococcus aureus and the worst against Rhizopus.The antibacterial effect of C-CS-PC film on Gram-positive bacteria was better than that on Gram-negative bacteria.The DPPH scavenging rate of C-CS-PC film reached 82.35%,which was about 50%higher than that of CS-control film,while ABTS+ radical scavenging rate was about 50%higher.Antioxidant property of C-CS-PC film was improved.FT-IR analysis showed that there were not new groups but intermolecular hydrogen bonds crosslinked between chitosan and procyanidins in the process of composite film formation,the results of TG and DSC analysis showed that the thermal stability of C-CS-PC is improved.Under different acid and alkaline condition,the color of C-CS-PC film changed significantly.The above results indicate that C-CS-PC membrane is a pH-responsive material with high antioxidant activity and antibacterial activity.The mechanism of procyanidins grafting onto chitosan at C6 site catalyzed by TEMPO-laccase oxidation system was studied.HPLC-MS was carried out for the intermediate products of laccase acting on procyanidins within different times,and the optimal addition time was determined to be between 30-60 min.The FT-IR and NMR analysis showed that the procyanidins were successfully grafted to the C6 site of chitosan,and the antibacterial structural units(-NH3)of chitosan were protected.The substitution degree of chitosan-procyanidins grafted derivatives(CS/PC-grafting derivatives)was calculated to be 35.67 with elemental analysis of C/N.The antibacterial activity and antioxidant properties of CS/PC-grafting derivatives were significantly improved.The antibacterial activity of Escherichia coli,Staphylococcus aureus and aspergillus Niger was increased by 85.36%,64.18%and 40.79%respectively.The antioxidant activity test results showed that CS/PC-grafting derivatives had significant scavenging effect on DPPH and ABTS+ free radicals.The DPPH and ABTS+ scavenging rate of CS/PC-grafting derivatives reached 88.63%and 86.33%,which was 190.02%and 156.55%higher than that of CS-control.Graphene oxide(GO)was loaded onto the chitosan-procyanidin graft film by spraying method,and "sandwich structure" of GO-chitosan/procyanidin multifunctional film(GO-G-CS/PC)was prepared.The physical,barrier antioxidant,antibacterial and pH response properties of GO-G-CS/PC film were characterized and tested.The results showed that Light resistance performance of GO-G-CS/PC film was obtained with the transparency decreased from 82.0%of CS-control film to 28.8%.The solubility of GO-G-CS/PC film was 31.44%lower than that of CS-control film.The mechanical properties of GO-G-CS/PC film were enhanced with the tensile strength and elongation at break were improved to 82.65Mpa and 5.34%.The water vapor transmission of GO-G-CS/PC film decreased to 432.18 g·m-2·d-1.SEM scanning results showed that the structure of GO-G-CS/PC film was the most compact due to the GO layer was closely bound to G-CS/PC layer.The thermal stability of GO-G-CS/PC film was improved by the maximum weight loss rate temperature was increased to 282? and the residual weight was 36.65%at 600?.GO-G-CS/PC film had the best antioxidant performance,with DPPH and ABTS+free radical scavenging rates reaching 80.23%and 85?65%,respectively.GO-G-CS/PC film owned excellent bacteriostatic performance similar to G-CS-PC film.GO-G-CS/PC film has obvious pH response performance consistently with visual observation.The sensory evaluation,pH value,total bacterial count,peroxide value and color of cheese were tested in a storage period(30 days).The results showed that the preservation effect of cheese pachaged with GO-G-CS/PC film was better than the other four packaging materials,and the sensory evaluation was the highest.On the 30th day of storage,the peroxide value of cheese was 1.65 meq/Kg,which was 25.33%and24.65%lower than that of PE film and CS-control film,which could delay the oxidative deterioration of cheese.The first-order kinetics reaction equation of cheese packaged with GO-G-CS/PC film was P=1.122e0.0095t(5?)and P=1.757e0.0194t(25?),which extended cheese preservation for 103 and 43 days respectively compared with PE film.GO-G-CS/PC film with high antioxidant and barrier properties has a good effect on cheese preservation and can be used as an excellent packaging material for dairy products.