Development And Characterization Of Composite Films Based On Nano-bacterial Cellulose

With the enhancement of people's awareness of environmental protection and health consumption,the environmental and food safety problems caused by synthetic packaging materials have received more and more attention in recent years.Therefore,biodegradable packaging film and even active food packaging film developed gradually.At present,the materials used for the preparation of biofilms mainly include protein,polysaccharide and lipids.However,the packaging films based on these materials mostly have poor mechanical properties,thermal stability and poor water resistance,which can't meet the demand for packaging film materials.In order to improve these deficiencies,many of materials with the better mechanical properties are added to these natural substrates to prepare a composite film.In addition,the food in the production,transportation,storage and sales process,due to the impact of external conditions,prone to oxidation,vitamin loss,odor,texture changes and microbial contamination.In order to solve these problems,people will add a certain amount of additives in food.However,some additives are easy to react with food components or have unpleasant taste or odor,thus affecting the sensory quality of food.In this study,nano-bacterial cellulose(BC)as a reinforcement agent was added into buckwheat distiller's dried grains(DDGS)protein and chitosan(CH)-epigallocatechin-3-gallate(EGCG)matrix with different dose to improve the mechanical properties,thermal stability and moisture resistance of DDGS protein and chitosan-EGCG films and slow down the release of EGCG from CH-EGCG active films.Viscoelasticity of film forming solution was analyzed by rheometer and the other properties were analyzed using scanning electron microscopy(SEM),Fourier Transform Infrared(FTIR)spectroscopy,differential scanning calorimeter(DSC)and texture analyzer.The optimized composite films were obtained eventually.The main results are as follows:(1)Nano-BC was used as a reinforcement agent,and the composite film based on DDGS protein that a byproduct of the brewing industry was prepared.The film microstructures showed that BC is compatible with protein matrix and endows the film with high rigidity.Differential scanning calorimetry(DSC)showed that BC can promote thermal stability of the composite films.BC promoted the transition from a Newtonian to a non-Newtonian fluid and the shear thinning behavior of protein-BC solution.Fourier Transform Infrared(FTIR)spectroscopy showed the main functional groups' absorption peaks shifted to lower wavenumbers.(2)Results of both FTIR and viscosity analysis proved the formation of intermolecular interactions through hydrogen bonds.Therefore,when adding 1.1%,1.6%,1.8%,and 2.0% BC to DDGS protein matrix,it can improve the physical and mechanical properties of films.These bonds affected film characteristics such as moisture content(MC),water solubility(WS),and water vapor permeability(WVP),which decreased with addition of BC.Tensile strength(TS)values of films containing 1.8% and 2.0% BC(14.98 ± 0.97 and 15.03 ± 2.04 MPa)were significantly higher than that of pure protein films(4.26 ± 0.66 MPa).(3)Different dose of nano-BC(5% and 10%)were added into CH matrix with 15% and 30% EGCG to prepare a novel antioxidant active film.BC had good compatibility with CH matrix according to SEM result.Differential scanning calorimetry(DSC)indicated that BC improved thermal instability of films caused by EGCG.Rheological properties,Fourier Transform Infrared(FTIR)spectroscopy analysis confirmed that formation of intermolecular interactions among CH,BC and EGCG though hydrogen bonds.(4)EGCG addition had a negative impact on water solubility(WS),tensile strength(TS),elongation at break(EAB).But nano-BC can significantly decrease WS from 26.54% to 20.80%,increase TS from 18.71 to 44.17 MPa and EAB from 2.72% to 7.34%.(5)The addition of nano-BC could slow down the release of EGCG from CH film,in which the release of CH-BC5-EGCG30 was about 12%,and the ABTS radical scavenging ability was higher.