| In recent years,building a delivery system with oil-in-water Pickering emulsion(OPE-1)stabilized by nanocrystal celluloses(NCC)as a template has become the hotspot of food,medicine,and other fields.However,the poor freeze-thaw stability of the OPE-1 limits its application.In this thesis,a new oleogel-in-water Pickering emulsion(OPE-2)was built using beeswax as the oleogelator.The microstructure,rheological property,and FT stability of the OPE-2 were characterized and determined.The relationship among the macroscopic rheological property,microstructure,and melting behavior of the emulsion,under static and the rheological field,was discussed.The freeze-thaw stable performance and the chemical stability and in vitro digestion properties as a delivery system for fat-soluble nutrients of OPE-2 were studied.The stability of OPE-2 is significantly improved.This thesis provides a theoretical basis for the further study of Pickering emulsions.(1)The soybean oleogel system was constructed by using beeswax as the oleogelator,and the influence of beeswax concentration on the microstructure,rheological properties,and thermal properties of the oleogel system was studied.The results showed that beeswax crystal is a needle or rod-shaped structure,which led to good gel properties of wax.When the beeswax concentration is above 2.0%,the oleogel was formed.With the increase of beeswax concentration,the length and width of wax crystals increased.However,due to the presence of molecular units with linear structures in beeswax,the overall lateral growth was less than longitude growth.The melting behavior of the oleogel system was dependent on beeswax concentration.With the increase of beeswax concentration,the gel-sol transition temperature of oleogel increased,and the enthalpy of melting during heating and crystallization during cooling increased.(2)The OPE-2 system,constructed by using the above oleogel as the dispersed phase and NCC as the stabilizer,was characterized.The results show that OPE-2 had a good storage stability in a wide range of beeswax concentration(2.0%-15.0%),oleogel fraction(0.10-0.50)and NCC concentration(0.1-0.9%).The increase of beeswax concentration from 2.0%to 15.0%(w/v)and the increase of oleogel fraction from 0.10 to 0.40 resulted in an increase in emulsion droplet size,viscosity,and gel strength.The increase of NCC concentration from 0.10%to 0.90%(w/v)resulted in a decrease in emulsion droplet size and an increase in viscosity and gel strength.OPE-2 showed a shear thinning behavior.The relationship between macroscopic rheological properties,micro structure,and melting behavior of the emulsion was observed.It was found that the rheological properties and melting behavior of the emulsion could be regulated by adjusting the droplet size of OPE-2.The Pickering stability mechanism was analyzed based on the results of laser confocal microscopy:at low concentration,NCC formed an interface film on the surface of the emulsion droplets,and the stability of the emulsion was improved by synergizing the space action and repulsive force;at high concentration,in addition to the above stability mechanism,NCC aggregates formed a three-dimensional network structure in the aqueous phase to play a stabilizing role.During storage,the change of G value of the OPE-2 had little relationship with G' value of the oleogel.We speculated that hydrogen bonds forming between NCC aggregates strengthed the three-dimensional network in the aqueous phase,and G' value of the OPE-2 increased during storage.The change in G' value during storage can be described by a first-order dynamic process.The gelation process of the emulsion during storage can be analyzed by the Arrhenius model.(3)The freeze-thaw stability of OPE-2 was studied and verified in a complex emulsified sausage system.The results showed that the freeze-thaw stability of the OPE-2 system was significantly improved compared with the traditional OPE-1 system.The reasons are as follows:The dispersion phase of OPE-2 was in a semi-solid state,and the ice crystals formed in the freezing process were difficult to penetrate into the oleogel phase,causing damage to the interface layer;Traditional Pickering emulsion produced a large number of ice crystals during freezing,forcing the fat droplets to gather in the concentrated unfrozen water phase and promoting the condensation and separation of the droplets from the oil phase during melting.Compared with pH,the ionic strength had a greater influence on the freeze-thaw stability of the emulsion,indicating that electrostatic force was the main driving force to maintain the stability of the emulsion system.Validation tests of freeze-thaw stability of OPE-2 added to complex emulsified sausage system showed that,compared with OPE-1,freeze-thaw stability of the emulsified sausage with OPE-2 containing 9.0%beeswax instead of animal fat was increased.The results provided a possibility for OPE-2 to be used in complex food systems to improve its freeze-thaw stability.(4)?-carotene(BC)is beneficial for human health.However,the low oxidative stability and bioavailability of hydrophobic BC limit its utilization as supplements in functional foods and pharmaceutical products.Herein a conventional OPE-1 and a novel OPE-2 were prepared to improve the chemical stability and bioavailability of BC.The freeze-thaw stability and physical stability of the Pickering emulsion with oleogel as internal phase was improved compared to the OPE-1.Thus,the storage life of the system could be improved.The OPE-2 presented higher droplets size than OPE-1,but they were more stable over a wide range of pH(4.0-8.0)and salt level(0.05-0.60 M).The chemical stability of BC encapsulated in OPE-2 was higher than that in OPE-1.For instance,the relative BC retention decreased from 100%to 71.16%/90.12%in OPE-1/2 after stored at 25? for 15 days.The BC bioaccessibility in OPE-2(68.17%±1.19%)was significantly improved compared with OPE-1(53.15%±1.36%).The results obtained indicated that OPE-2 were probably an effective delivery system for hydrophobic and indigestible bioactive compounds. |
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