| Pickering emulsions show great potential for applications in food,pharmaceuticals,cosmetics,and agriculture because of their stability,low toxicity,environmental friendliness,and modifiable functional properties.Natural protein-polysaccharide composite particles perform better than traditional inorganic or synthetic particles in stabilizing Pickering emulsions and avoiding the biosafety issues associated with inorganic or synthetic particles.Most of these natural protein-polysaccharide complex particles are derived from plants,but rarely from microorganisms.However,microorganisms are abundant renewable resources in nature,among which lactic acid bacteria as probiotics have a high market value and broad application prospects,and lactic acid bacteria and their metabolites have become one of the hot spots in food science research.Therefore,if we can extract naturally occurring protein-polysaccharide composite nanoparticles using lactic acid bacteria and develop Pickering emulsions with them as solid particles not only can meet their applications in various fields such as food,medicine and cosmetics,but also provide ideas for the development of new Pickering particles.In this paper,natural protein–polysaccharide hybrid nanoparticles（PPH NPs）were successfully isolated and extracted by fermenting whey with Lactobacillus plantarum LCC-605 as the fermenting strain,and their properties were comprehensively investigated.Subsequently,Pickering emulsion was successfully prepared with PPH NPs as stabilizers,and its stabilization mechanism was investigated.The Pickering emulsion was used to encapsulate curcumin and compounded with bacterial cellulose（BC）to prepare a new smart packaging film（BC-PE-Cur）with UV-barrier,water vapor barrier,antibacterial,antioxidant,p H indication,and other functions,which was applied to the freshness packaging of balsa fish.The specific research work is as follows:（1）Preparation and characterization of PPH NPs.Lactobacillus plantarum LCC-605 was used as the fermentation strain,which was inoculated into whey for fermentation,and natural protein-polysaccharide composite nanoparticles were isolated and extracted from the fermentation broth.PPH NPs are negatively charged spherical particles with a diameter of about129 nm,mainly composed of 37.7%protein and 7.3%polysaccharide,containing a variety of functional groups including-OH,-NH,-COOH,etc.They can maintain their colloidal stability without drastic changes in their morphology and particle size in aqueous solutions of p H 1～11and Na Cl solutions of 0～500 m M.（2）Preparation,characterization and formation mechanism of oil-in-water Pickering emulsions stabilized by PPH NPs.PPH NPs showed good emulsification ability in the preparation of oil-in-water Pickering emulsions,and Pickering emulsions stabilized by PPH NPs could be successfully prepared in the range of particle concentration of 0.4～1.0%and oil volume fraction of 0.1～0.7.The emulsion has good rheological properties,is gel-like,has high viscosity,has typical shear thinning behavior,and is a pseudoplastic non-Newtonian fluid.In addition,the emulsion stabilized by PPH NPs also has good stability in a wide range of environmental conditions at p H 3～11,ionic strength of 0～200 m M,and temperature of 25～60°C.The formation mechanism of Pickering emulsion stabilized by PPH NPs was observed by confocal laser scanning microscope（CLSM）and cryo-scanning electron microscopy（Cryo-SEM）.The results showed that the PPH NPs adsorbed at the oil-water interface,forming a dense spatial barrier and forming a 3D network structure in the continuous phase to further prevent the collision and aggregation of droplets,and the PPH NPs also formed a stable bridging structure between oil droplets to maintain the stability of the emulsion.（3）Preparation,characterization and application of bacterial cellulose composite films loaded with curcumin-embedded Pickering emulsion stabilized by PPH NPs.Multifunctional food packaging films were prepared by encapsulating curcumin in Pickering emulsions and blending the emulsions with bacterial cellulose.The mixing of emulsion makes the film thicker,roughness increases,and spherical oil droplets are attached to the film surface,while the film has a laminar pore structure inside.As the oil content in BC-PE-Cur films increases,the tensile strength of the films decreases,the elongation at break increases,and the light transmittance and water vapor transmission rate decreases,indicating that BC-PE-Cur films has better UV and water vapor barrier properties.In addition,BC-PE-Cur films scavenged 27%of DPPH radicals and 74%of ABTS radicals,and inhibited 96%of Escherichia coli（E.coli）and 100%of Staphylococcus aureus（S.aureus）at an initial OD600=0.05 concentration,indicating that BC-PE-Cur films have good antioxidant and antibacterial properties.When BC-PE-Cur films were used to pack Basa catfish,after 3 days of storage,the total volatile salt-based nitrogen（TVB-N）value of Basa catfish packed with BC-PE-Cur films was only 9.586 mg/100 g compared to unpacked Basa catfish,which significantly delayed the spoilage of the fish.In addition,during the storage of Basa catfish,the BC-PE-Cur films underwent a significant color change during fish deterioration and served as an intelligent indicator of the freshness of meat products. |
