Study On The Properties Of Bacterial Cellulose Nanofibers Modulating The Properties Of Konjac Gum-based Edible Composite Films

With the increase of people's awareness of environmental protection and attention to food safety,food packaging has become the focus of people's attention,among which synthetic packaging brings convenience to people but also causes environmental pollution,waste of resources,food safety and other problems.Thus,the edible packaging based on natural biomacromolecules such as polysaccharides,proteins and lipids,has increased significantly.Furthermore,edible film is safe,non-toxic,and has the advantages of edibility,freshness preservation and degradability.From the perspective of sustainable development,it has become a trend to replace traditional synthetic packaging materials.However,polysaccharide and protein-based edible films are sensitive to water,presenting poor barrier properties,mechanical properties,and thermal stability,which limits their wide application.In addition,there are many problems associated with food production,transportation,marketing and storage,including water loss,vitamin loss,texture damage and microbial contamination.Therefore,the objective of the present research was to improve the propreties of edible films based on konjac glucomannan(KGM)by bacterial cellulose nanofibers(BCNs)to regulate the characteristics of the composite films,for improving the physical properties of and endowed its functionality,systematically studied the nanocomposite films,emulsion films,active films.The barrier properties,mechanical properties and antioxidant-antibacterial activities of the composite films were systematically studied,and the structure-activity relationship between the microstructure and physical properties of the KGM-based films was investigated.The main research conclusions were as follows:(1)BCNs were obtained from bacterial cellulose(BC)by hydrolysis,and then BCNs were added into KGM film-forming solution to prepare nanocomposite films.The rheological properties suggested that the film-forming solutions were all non-Newtonian fluids,and the elastic modulus(G?)G?).Scanning electron microscopy(SEM)showed that BCNs were well distributed in the nanocomposite films,and the surface roughness of the nanocomposite films increased with the increase of BCNs content analysed by atomic force microscopy(AFM).Furthermore,fourier transform infrared spectroscopy(FTIR)showed that nanocomposite films were formed mainly through hydrogen bonding between KGM and BCNs.Meanwhile,the crystallinity and thermal stability of the nanocomposite films were improved as the content of BCNs increased by X-ray diffraction(XRD)and thermogravimetric analysis(TGA).In addition,with the content of BCNs increasing,the moisture content(MC),water solubility(WS)and water vapor permeability(WVP)of the nanocomposite films decreased,the tensile strength(TS)increased,and the elongation at break(EAB)and oxygen permeability(OP)first increased and then decreased.Therefore,BCNs is a promising nano-reinforce agent,which has great application potential in food packaging field.(2)Bacterial cellulose nanofibers/soybean protein isolate(BCNs/SPI)composite colloidal particles were prepared by anti-solvent method,which was used to stabilize Pickering emulsions with the oil phase(v/v)of 10%,30%,50%and 70%.Then,the prepared Pickering emulsions were added into film-forming solution to fabricate emulsion films,keeping the same final oil content in all KGM-based emulsion films.The rheological properties showed that the film-forming solutions of emulsion films were all non-Newtonian fluids,and at low frequencies G?G" displayed a gel behavior.The microstructure analysises(SEM and AFM)suggested that the KGM-based films became uneven and rough after adding Pickering emulsion with different oil phases.However,it was observed that the oil droplets wrapped in Pickering emulsion were evenly dispersed on the surface of emulsion films by confocal laser scanning microscopy(CLSM).Contact angle experiment showed that the addition of Pickering emulsion significantly improved the hydrophobicity of KGM-based emulsion films,and thermogravimetric(TGA)analysis suggested that the thermal stability of emulsion film was significantly improved as compared with that of pure KGM film.With the increase of oil phase in the Pickering emulsion,the moisture content(MC),water solubility(WS)and water vapor permeability(WVP)of KGM-based emulsion films decreased,while the oxygen permeability(OP)and tensile strength(TS)increased,and the elongation at break(EAB)first increased and then decreased.Thus,the oil phase of Pickering emulsion has a significant effect on the properties of KGM-based emulsion films.(3)The effects of different emulsifiers(Tween 80,BCNs/SPI composite colloidal particles)and loaded thyme essential oil(TEO)Pickering emulsion stabilized by BCNs/SPI composite colloidal particles on KGM-based active films were investigated.Scanning electron microscopy(SEM)showed that the surface of the active films with TEO-Pickering emulsion was smoother than other KGM-based active films,and confocal laser scanning microscopy(CLSM)suggested that the oil droplets were well distributed on the active films stabilized by TEO-Pickering emulsion.Furthermore,the addition of emulsifier and Pickering emulsion improved the surface hydrophilicity,moisture content(MC),water solubility(WS),water vapor permeability(WVP),oxygen permeability(OP),color characters and mechanical properties of KGM-based active films.Moreover,the active films based on KGM possessed antioxidant and antimicrobial activites.In particular,the release property of the KGM-based active film were significantly improved by adding TEO-Pickering emulsion.This study provides a theoretical basis for improving the physical properties,antioxidant-antimicrobial activities,and release property of KGM-based composite films.