| The structure,processing characteristics,and nutritive functional properties of proteins and polysaccharides alone has been clearly revealed.Nevertheless,the study of the interactions between food components plays a key role in developing novel food ingredients and enhancing the functional properties of individual food components.Therefore,understanding the interaction behavior between proteins and polysaccharides,developing the functional properties of their complex coacervates,and constructting composite ingredients with specific structures and functions.This not only has important application significance in solving the narrow range of natural food ingredient selection,upgrading food process and designing new product,but also conforms to the green,healthy and sustainable development direction of the food industry.Based on those considerations,ovalbumin(OVA)and carboxymethyl cellulose(CMC)were investigated in this work,which are rich sources and widely used in the food industry.After the OVA/CMC complex coacervation behavior was explored,the application potential of micro/nano-scale self-assembled complex coacervates of OVA/CMC in stabilizing high internal phase emulsions and encapsulation of bioactive substances was thoroughly investigated.Subsequently,the effect of electrostatic complexation with CMC on the thermally induced aggregation and gelation behavior of OVA was evaluated.Furthermore,the relationship between strength,microstructure,and water holding capacity of OVA/CMC electrostatic complex thermally-induced gels and their regulatory strategies were given.The main research results of this work are as follows:1.The OVA/CMC complex coacervation behavior were revealed mainly using turbidity tracking,isothermal titration calorimetry and dynamic rotational rheometer.The results showed that OVA and CMC can form complexes or coacervates spontaneously with p H changes through the electrostatic interactions driven by enthalpy.Specially,the impact of ionic strength on OVA/CMC complex coacervation exhibited multiple effects.When CNa Cl=20 m M,the binding between OVA and CMC showed the highest stoichiometry,binding constant,enthalpy change,and elastic modulus.When CNa Cl>200 m M,the complexation of OVA and CMC changed from endothermic to exothermic,suggesting a transition from enthalpy-driven to entropy-driven.In addition,since CMC 1.2 has a higher charge density than CMC 0.7,OVA and CMC 1.2 have stronger binding ability and resistance to salt ion shielding,and the OVA/CMC 1.2 coacervates showed a more compact microstructure and a higher viscoelastic modulus.2.The OVA/CMCs nanoparticles were prepared by heating(90 ?,30 min)the electrostatic self-assembly complexes between OVA and CMC of different charge density(CMC 0.7 and CMC 1.2)at p H 4.4.The results showed that the OVA/CMC 0.7 nanoparticles exhibited larger size and lower surface net potential than OVA/CMC 1.2 nanoparticles.Atomic force microscopy(AFM)imaging and ultra-small angle X-ray scattering(USAXS)results suggested that the shape of the particles was approximately spherical,and the structure of OVA/CMC 1.2 nanoparticles was more compact than that of OVA/CMC 0.7.The pyrene fluorescent probe indicated that the OVA/CMC 1.2 nanoparticles had a stronger hydrophobicity than OVA/CMC 0.7 nanoparticles in the range of p H 4-7.As the p H and the ionic strength increased,the average diameter of OVA/CMC nanoparticles would increase,while the average size of the nanoparticles did not change significantly after 30 days of storage at room temperature(<400 nm).The interfacial rheological experiments showed that the permeation and rearrangement rates of OVA/CMC nanoparticles decreased significantly at oil-in-water interface,and the surface pressure and interfacial dilatational modulus were lower than the native OVA/CMC complexes.The OVA/CMC spherical nanoparticles described above were used to encapsulate resveratrol to enhance its photostability and bioaccessibility.The encapsulation efficiency and loading capacity were around 26% and 13 ?g/mg for OVA/CMC nanocomplexes,and evidently increased to around 70% and 35 ?g/mg for OVA/CMC nanoparticles,respectively.The major driving forces for resveratrol encapsulation were hydrogen bonding and hydrophobic interaction.Both the formulations could improve the photostability of trans-resveratrol when exposed to UV light,and the nanoparticles were more effective.Moreover,the release profile of resveratrol from the nanocapsules in vitro simulated gastrointestinal tract was greatly enhanced and could be well fitted by Higuchi kinetic model and Korsmeyer-Peppas model,indicating a Fickian diffusion release mechanism.Compared to native resveratrol,the bioaccessibility of resveratrol embedded in nanocomplexes and nanoparticles was increased to 60% and 80%,respectively.This not only greatly improved the bioavailability of resveratrol by single-component materials(OVA or CMC),but also provided new options for the protection and delivery of similar active substances.3.The composition,microstructure,and rheological properties of complex coacervates formed at different p H values(3.0,3.5,and 4.0)were investigated using compositional analysis,scanning electron microscopy,dynamic rheometer,and laser confocal imaging,respectively.The ability and mechanism of those complex coacervates to stabilize high internal phase emulsions were evaluated.The results showed that the content of protein and polysaccharide in OVA/CMC complex coacervates decreased with the increasing of p H value,and the microscopic network structure of the complex coacervates changed from dense to loosen,which was mainly due to the weakening of the electrostatic interaction between OVA and CMC.At the same time,due to the higher charge density of CMC1.2,the OVA/CMC1.2 complex coacervates exhibited a more dense microscopic network structure and viscoelastic properties than OVA/CMC0.7.The results of the investigation on stable high internal phase emulsions of complex coacervates formed at different p Hs of OVA/CMC showed that the strong electrostatic recombination between OVA and CMC leads to poorer oil binding ability and emulsion stability of complex coacervates.This phenomenon was particularly evident in the emulsion system stabilized by OVA/CMC1.2 complex coacervates.It can be explained that mainly due to the strong electrostatic binding,which seriously hindered the adsorption,penetration,and rearrangement of protein molecules at the oil-in-water interface.In contrast,the moderate electrostatic interaction at p H 4.0 in OVA/CMC complex coacervates exhibited an excellent high internal phase emulsion(80% oil phase)stabilizing ability.This provided a new strategy for the stabilization of high oil phase food systems.4.The effects of electrostatic complexation on the thermally induced gelation behavior of OVA were investigated using a dynamic rheometer and laser confocal imaging technology combined with fractal analysis.It was found that electrostatic complexation with CMC greatly inhibited OVA thermally induced gelation,and CMC1.2 with higher charge density exhibited stronger inhibition than CMC0.7.The rheological fractal analysis results showed that the thermal gels of OVA/CMC0.7 and OVA/CMC1.2 electrostatic complexes were in the transition region.In addition,with the OVA-CMC ratio rising from 10:1 to 40:1,the fractal dimensions of OVA/CMC0.7 and OVA/CMC1.2 thermally induced gels increased from 1.83 and 1.75 to 2.17 and 2.08,respectively.This indicated that an increasing in the proportion of protein will lead to a more compact fractal aggregate structure,so that the gel exhibited a higher elastic modulus(G').On the other hand,the shielding effect of salt ions can enhance the thermo-gel strength of OVA/CMC complexes.However,when the salt ions(100 m M)completely dissociate the protein molecules from the polysaccharide chain,the apparent viscosity of the polysaccharide exerts a large influence on the thermo-gelation of OVA.The CMC0.7 with a lower charge density exhibited a stronger ability to suppress the thermogelation of OVA than CMC1.2 because of its large apparent viscosity.This new type of OVA/CMC electrostatic composite thermogel can provide a potential solution for the preparation of fat replacer.5.The relationship between the structure,strength and water holding capacity of the thermally induced gels of OVA/CMC electrostatic complexes were investigated by gradient centrifugation,confocal laser scanning and scanning electron microscopy,respectively.The results showed that the electrostatic complexation with polysaccharides resulted in a more uniform and dense structure of the OVA thermo-induced gel,and displayed better water-holding performance,while the Young's modulus of the gel was significantly decreased(P<0.05).These results were closely related to the electrostatic interaction that inhibited the formation of large aggregates of protein in the heat-induced process,and the higher charge density of CMC1.2 exhibited stronger suppression ability for the gel structure and properties.In addition,the use of salt ion shielding effect can increase the strength of the gel to a certain extent.When the ionic strength was 200 m M,the Young's modulus of OVA/CMC0.7 and OVA/CMC1.2 gels were increased from 26 k Pa and 21 k Pa to 45 k Pa and 38 k Pa,respectively.However,it also increased the roughness and the pore size of the microstructure of the gel,resulting in a reduction in the water holding capacity of the OVA/CMC 0.7 and OVA/CMC 1.2 gels from 50% and 54% to 29% and 34%,respectively.Furthermore,the water-holding capacity of the gels were closely related to the pore size and strength of the structure.The effective permeability coefficient(k1)and water flux coefficient(k2)of the gel have a significant positive correlation with the pore size of the gel structure.This indicateed that the adjustment of the water retention of the gel was mainly controlled by the pore size of its microstructure.The above results can provide new references for the regulation of texture and sensory properties of protein-based hydrogels food systems. |
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