Preparation And Performance Study Of Wheat Bran Cellulose Nanocrystals-Soy Protein Isolate Composite Packaging Film

With the increasing demand of environmental protection,the development of natural renewable,degradable,and environmentally friendly edible films to replace traditional synthetic plastic packaging has become a consensus in the field of food packaging.Soy protein isolate（SPI）film has great potential in the application for food package.However,shortcomings such as insufficient performance and single function severely limited the practical application of SPI film.Polysaccharide blending modification technology played an extremely important role in improving the performance of protein-based films.Based on this,this thesis explored the blending modification mechanism of SPI film by the wheat bran cellulose nanocrystals（CNC）,evaluated the storage stability of the composite films,and prepared the nanocomposite packaging films with antibacterial/antioxidant activity,which could provide a theoretical basis for the development and application of functional protein-based edible films.The main research contents and experimental results are as follows:（1）Preparation and characterization of wheat bran cellulose nanocrystals:The acid hydrolysis method was used to separate and prepare CNC from wheat bran;and the influence of different acid hydrolysis time（30,60 and 90 min）on the physicalchemical properties and cytotoxicity of CNC was investigated.The results showed that the size,yield and thermal stability of wheat bran CNC gradually decreased with acid hydrolysis time,while the aspect ratio gradually increased.CNC still retained the basic chemical structure of cellulose and the typical cellulose I crystal structure.The crystallinity reached 70.32%after acid hydrolysis for 60 min.Wheat bran CNC had good water dispersibility and adsorption properties（water,oil and heavy metals）.When the concentration did not exceed1000μg/m L,CNC had no obvious cytotoxicity to Caco-2 cells.（2）The effect and mechanism of cellulose nanocrystals on the properties of soy protein isolate film:The CNC-SPI nanocomposite films were prepared by blending method;and the effects of different CNC additions（0～1.00%）on the performance of SPI film and the related mechanisms were discussed.The results showed that a proper amount of CNC（0.50wt%and 0.75 wt%）improved the tensile strength,oxygen/water vapor barrier properties and water resistance of the SPI film,reduced the elongation at break,but had no obviously effect on the film thickness,water content and optical properties.CNC limited the mobility of water molecules in the film and improved the viscoelastic properties of the film-forming solution.CNC promoted the formation of a dense and uniform ordered network film structure by inducing the conformational rearrangement of protein molecules and enhancing the interactions between molecules,thereby improving film performance.（3）Storage stability of the cellulose nanocrystals-soy protein isolate composite film:Two composite films were prepared with wheat bran cellulose and CNC as reinforcing agents,and the dynamic change of the basic performance of composite films were investigated under different storage time（1,30,60,and 90 d）.The results showed that with the extension of storage time,the tensile strength,water vapor barrier properties,water resistance and transparency of SPI film had a downward trend,and the elongation at break and total color difference had an upward trend,while the film thickness did not change significantly.The introduction of enhancers（especially CNC）improved the storage stability of SPI film to a certain extent.（4）Preparation and performance evaluation of antibacterial composite film based on zinc oxide nanoparticles:The antibacterial nanocomposite films reinforced with carboxylated CNC,zinc oxide nanoparticles（ZnONP）,CNC/ZnONP mixture（physical hybrid）and CNC@ZnONP nanohybrid（in-situ growth）were developed;and the physicalchemical properties,antibacterial activity and practical application prospects of the composite films were comprehensively evaluated.The results showed that ZnONP reduced the elongation at break and water solubility of the SPI film,but had no significant effect on the tensile strength,oxygen/water vapor barrier properties,surface hydrophobicity,total color difference,opacity,crystal structure and viscoelastic properties.The composite films containing ZnONP（ZnONP,CNC/ZnONP and CNC@ZnONP）inhibited the growth of E.coli and S.aureus by destroying the bacterial cell structure,and reduced the total number of colonies and total volatile basic nitrogen（TVB-N）content of pork samples during storage.Among them,CNC@ZnONP composite film had a significant inhibitory effect on the migration behavior of zinc ions,and had the potential to be used to extend the shelf life of fresh pork.（5）Preparation and performance evaluation of pH-responsive antioxidant composite film based on curcumin nanocapsules:The pH-responsive antioxidant nanocomposite films strengthened by CNC,curcumin nanocapsules（CurNC）,CNC@CurNC and CNC@Cur were developed;and the physicalchemical properties,curcumin release characteristics,antioxidant activity,color responsiveness and practical application value of the composite films were comprehensively evaluated.The results showed that CurNC reduced the brightness and transparency of the SPI film,but the tensile strength,elongation at break,oxygen/water vapor barrier properties,surface hydrophobicity,water solubility and crystal structure did not change significantly.The addition of CNC enhanced the internal structure of the film,which was conducive to the slow release of curcumin.CurNC-containing films（CurNC film and CNC@CurNC film）had the strongest antioxidant activity,which may be because the thermal stability of CurNC was higher than that of pure curcumin.In addition,CNC@CurNC film showed good color responsiveness to pH and NH₃,and could reduce the TVB-N content of stored shrimp and realize visual and real-time monitoring of its freshness.