Study On Properties Of Whey Protein Based Cellulose Composite Films

Whey protein-based edible films have been studied widely.However,there are some drawbacks in the barrier ability to water vapor and mechanical properties of whey protein concentration?WPC?films.The blending modification of cellulose can form intermolecular forces and enhance mechanical properties of WPC film.Transglutaminase?TGase?can make covalent cross-linking of proteins and enhance mechanical properties and barrier properties of WPC film.However,little attention has been paid to the coexistent effect of NCC and TGase on WPC-NCC composite films.In the present work,this study was mainly based on the effect of nanocrystalline cellulose?NCC?and TGase on WPC film to determine the suitable composite film forming conditions,and was conducted structural characterization and packaging cheese experiment for the composite films,which laid a theoretical foundation for the practical application of WPC based cellulose composite films for the future development.Firstly,the film forming condition of the composite film were determined by measuring mechanical properties,transmittance and water vapor permeability?WVP?of the composite films.The suitable conditions were achieved as the following conclusions.WPC concentration is 10%?w/v?of the film solution,NCC content is 10%?w/w?of WPC.Glycerin as a plasticizer was introduced into the film-forming solution at 45%?w/w?of WPC.TGase with the concentration of 9 U/g protein was added into the mixture solution to catalyze the reaction at 50°C for 2h.Tensile strength?TS?of the composite film prepared as the above conditions was 2.38 MPa,elongation at break was 86.75%,transmittance at 600 nm was55.5%,water vapor permeability?WVP?was 4.62×10^-12 gmPa^-1s^-1m^-2.Comparing with WPC film,tensile strength and elongation at break of the composite film prepared with the above conditions increased by 1.02 times and 9.74%,WVP decreased by 12.59%,and transmittance didn't change significantly.Secondly,the protein components,secondary structure,protein conformation,thermal properties and microstructures of WPC based film were studied by SDS-PAGE,fourier infrared spectroscopy?FTIR?,fluorescence spectroscopy,differential scanning calorimetry?DSC?and scanning electron microscope?SEM?.The results showed that the cross-linking of WPC caused by TGase produced macromolecular substances,and the content of macromolecular substances increased as the amount of TGase increased.Hydrogen bond existed between the protein matrix and NCC in the composite film.The secondary structure of WPC was changed significantly.The addition of TGase and NCC resulted in the increase of?-helix structure and reduction of random coil significantly,which transformed protein structure into a stable and ordered state.The polarity of the microenvironment around tryptophan increased,which indicated that the protein conformation changed.The thermal denaturation temperature of the composite film was enhanced with the addition of NCC and TGase.Moreover,the treatment of TGase and the addition of NCC reduced the pore size and the number of pores on the surface of the composite film,forming a dense and uniform network structure.Finnally,the packing effect of different WPC based film materials on cheese were studied by the packaged cheese experiments.The results showed that WPC-NCC-TG composite films had a better packaging effect in WPC based films.During the storage period of cheese,the characteristics of cheese package by WPC-NCC-TG composite film changed the least,the weight loss rate reached to 3.09%,the pH value decreased from 4.70 to 4.15,and the OD_532nm value increased from the initial 0.040 to 0.047.The pH of the cheese sample solution and the degree of fat oxidation were comparable to those of the PE film packaging samples within 10 days.The packaged cheese samples of WPC-NCC-TG composite film and PE film were accepted by people for up to 20 days.