The Preparation And Application Of Cyclodextrin/chitosan Based Pickering Emulsion

Pickering emulsion is a kind of emulsion where traditional emulsifiers are replaced by solid particles,which are adsorbed at the oil-water interface,thereby preventing oil droplets from agglomerating,and forming a stable emulsion.Compared with traditional emulsions,Pickering emulsions do not include chemical emulsifiers and have received widespread attention due to their excellent stability.As people’s requirements for food health are getting higher and higher,using food-grade solid particles to stabilize Pickering emulsions has gradually become a research trend.Chitosan（CS）is a natural linear polysaccharide with multiple amino groups and positive charges on the surface,with the characteristics of antibacterial and mucosal properties.The hydrophobic cavity of cyclodextrin can have host-guest recognition effect with active substances,thus can be used in emulsions to improve the encapsulation capacity for active substances.In this research,phytic acid-modifiedβ-cyclodextrin（PA-CD）was prepared by cross-linkingβ-cyclodextrin（β-CD）with phytic acid（PA）,and chitosan-phytic acid-cyclodextrin（CS-PA-CD）nanoparticles were prepared through the anti-solvent co-precipitation method.The size,morphology and physicochemical properties of nanoparticles were characterized.The CS-PA-CD nanoparticles were further used to prepare oil-in-water（O/W）Pickering emulsions,and the physicochemical properties,rheological properties and stability of the emulsion were explored.Finally,the Pickering emulsion system was used to encapsulateβ-carotene,and its encapsulation,digestion and absorption performance were explored.The main results are as follows:Using PA andβ-CD as raw materials,PA-CD was prepared by dry heat reaction,and CS-PA-CD nanoparticles were prepared by co-precipitation with CS through anti-solvent method.The physicochemical properties were characterized.Fourier transform infrared spectroscopy（FT-IR）spectra showed that CS-PA-CD nanoparticles appeared a new peak of-NH₂ at 1540cm^-1,confirming the successful cross-linking between PA-CD and CS.Compared withβ-CD,the number of characteristic peaks of CS-PA-CD in the X-ray diffraction（XRD）spectra was reduced and the peaks were broadened,indicating that the crystal structure changed after reactions.The results of thermogravimetric analysis（TGA）showed that the thermal stability of PA-CD and CS-PA-CD was enhanced compared withβ-CD and CS.By optimizing the preparation conditions,it was found that when the raw material ratio of PA-CD:CS was 2:1（w/w）,the reaction temperature was 50°C,and the reaction time was 24 hours,the nanoparticles had the smallest particle size of 433.20 nm.Scanning electron microscope（SEM）images showed that the particle morphology was spherical.The Zeta potential of CS-PA-CD nanoparticles increased with decreasing ratio of PA-CD to CS.The results of the encapsulation of curcumin showed that when the PA-CD:CS ratio was 1:2,the encapsulation efficiency of curcumin in CS-PA-CD nanoparticles was up to 99.29±2.22%,indicating a good encapsulation capability.When the particle concentration was 2.0%and the oil phase fraction was 55%,the stability stayed well after 6 months of storage.The O/W Pickering emulsion stabilized by CS-PA-CD nanoparticles was prepared,its emulsion properties were investigated,and the effects of particle concentration and oil phase fraction on the emulsion were studied.When the particle concentration was 1.0%（w/v）and the oil phase fraction was 50%（v/v）,a stable emulsion was observed.The emulsion droplet size decreased from 6.69±0.35μm to 0.83±0.07μm with the increase of particle concentration,and increased from 0.65±0.06μm to 4.05±0.53μm with the increase of oil phase fraction.The change of the Zeta potential value of oil droplets had no obvious correlation with the stability of the emulsion system.The results of confocal laser microscopy（CLSM）showed that the emulsion droplets were regular spherical with good distribution uniformity.The rheological analysis of the emulsion showed that the Pickering emulsion stabilized with CS-PA-CD nanoparticles was shear-thinning of non-Newtonian fluid with a viscoelastic gel structure.Then,the influence of different environmental factors on the emulsion stability was explored,and the results showed that with the increase of salt ion concentration,the emulsion droplets aggregated and slightly delaminated.The emulsion remained stable in the temperature range of 30℃-70℃,and the particle size did not change significantly.The emulsion stability was greatly affected by p H value and exhibited a certain p H sensitivity,yet remained stable around p H 6.0.Using Pickering emulsion stabilized by CS-PA-CD nanoparticles as carrier,β-carotene was embedded,and the encapsulation and digestive absorption performances ofβ-carotene were studied.A stable emulsions can be obtained when the particle concentration was 2.0%（w/v）and the oil phase fraction was 60%（v/v）.The appearance of the emulsion was uniform orange-yellow,and the average particle size of the emulsion decreased with the increase of particle concentration and oil phase fraction,which was further confirmed by the microscopic images of the emulsion.The Pickering emulsion system stabilized by CS-PA-CD nanoparticles had a good encapsulation ability.The encapsulation efficiency ofβ-carotene increased with the increase of particle concentration and oil phase fraction,and reached the maximum of 97.66±1.18%when the particle concentration was 2.0%and the oil phase fraction was 50%.The digestion characteristics of the emulsion system were investigated by in vitro simulated digestion model,and the results showed that the bioaccessibility ofβ-carotene in the emulsion system was higher than that in soybean oil.The emulsion maintained good stability at different temperatures,and the retention rate ofβ-carotene decreased slightly with the increase of temperature and reached 84.19±0.92%after treatment at 70℃.The retention rate ofβ-carotene in the emulsion after treated by UV laser decreased with the increase in irradiation time,yet of all samples were higher than that in soybean oil.After 3 months of storage at room temperature,theβ-carotene embedded in the emulsions still had a good retention rate.The above results indicated that the Pickering emulsion system stabilized with CS-PA-CD nanoparticles had good encapsulation ability of active ingredients.