Fabrication,Characterization And Structure-Property Study Of Gliadin-Based Pickering Emulsions And Hierarchical Porous Materials

Emulsified systems and their derivatives hierarchical porous materials have attracted broad interest in many fields such as food,biology,pharmaceuticals,and agriculture.However,inorganic particles and traditional surfactants are still the mainstream stabilizers in emulsification systems,which is contrary to the concept of clean-label food.Furthermore,precise adjustment of pore structure and enhancement of mechanical properties through safe non-polymeric methods are two significant challenges in porous materials research.For the above problems,this research aimed to develop a variety of protein-based Pickering emulsions and to prepare corresponding biocompatible porous materials using Pickering soft templates.Here,Gliadin-based particles were prepared by anti-solvent method using the widely sourced and cost-effective raw material.Colloidal particles were used as stabilizers,further regulating the interfacial structure to construct stable Pickering oil-in-water（O/W）,water-in-oil（W/O）,oil-in-water-in-oil（O/W/O）,and other emulsified systems,the physicochemical properties of these systems were systematically studied,and the relationships between microstructures and macroscopic properties of the systems were established.Afterwards,to precisely adjust the pore characteristics,Pickering templates were used for the preparation of hierarchical porous materials,and the continuous phase structures of the emulsification system were further strengthened by non-chemical reactions such as the Hofmeister effect to obtain green porous materials with excellent mechanical properties,safety and non-toxicity.The significant results are as follows:1.Starting from the Pickering stabilization mechanism,Pickering oil-in-water（O/W）emulsions were prepared with gliadin/PA hybrid particles（GPHPs）stabilizers.The relationship between the microstructure of the emulsion and its macroscopic properties was established,and the purpose of regulating the oxidation and digestion of emulsified oil was achieved.The special affinity between proline-rich gliadin and proanthocyanidins（PA）was used to design dual-function GPHPs with both antioxidant and stabilizing interface functions.The addition of PA affected the self-assembly behavior of particles and benefited the interfacial adsorption of GPHPs to corn oil droplets.The interfacial dense layer consisting of GPHPs served as a valid barrier retarded lipid oxidation inside Pickering emulsion under thermally accelerated storage and simulated gastrointestinal（GI）tract.Thereby,according to results from HPLC and GC,oxidative markers including hexanal and malondialdehyde were reduced significantly.During digestion,the free fatty acid（FFA）release decreased by 55%from 87.9%（bulk oil）to 39.5%（Pickering emulsion）.By studying the digestion and oxidation characteristics of the emulsified oil,the interfacial structure was thus related to the physical and chemical properties of the emulsion,which provided a theoretical basis for the preparation of subsequent Pickering emulsification systems.2.Pickering O/W emulsions have been extensively studied,but research on food-grade Pickering W/O emulsions is very limited due to the lack of suitable stabilizers.To address this problem,hydrophobic ethyl cellulose（EC）was used to alter the wettability of hydrophilic Gliadin thus to prepare neutral hydrophobic,biocompatible,biodegradable hybrid particles（GECPs）.Edible Pickering W/O emulsions were developed using GECPs as the stabilizer.The characterizations of GECPs indicated that the gliadin-to-EC ratio was highly related to colloidal properties of GECPs include the particle size,contact angle,and dynamic interfacial tension,thus to afftect stabilities of emulsions.The most stable emulsions were obtained when the gliadin-to-EC ratio was 2:1.Using CLSM,the microstructure showed that GECPs formed a particle layer at the interface and acted as a physical barrier,thus contributing to the stability of emulsions for at least two years,besides emulsions were stable at particle concentrations higher than 1.5%,and emulsion stability increased with particle concentration,while emulsions prepared at low p H(（3.0-4.0）were more stable.In addition,the water phase fraction（?）of W/O emulsions can reach 50 wt.%,and the phase inversion of emulsions from W/O to O/W occurred at 55 wt.%water,this discovery laid the foundation for the construction of Pickering double emulsions.3.Theoretically,Pickering double emulsions have fancy properties due to their internal compartmentalized structure,while obtaining double emulsions with long-term physical stability by a simple and convenient method is still a great challenge.In the previous chapter,it was found that GECPs can stabilize both W/O and O/W interfaces.In this chapter,Pickering double oil-in-water（O/W/O）emulsions were prepared by a simple one-step emulsification method using GECPs as the sole stabilizer.The effects of water phase fraction（?）,ECP concentration and oil phase type on the properties of Pickering O/W/O double emulsions were systematically studied.Briefly,the emulsion changed from O/W/O into O/W types at water mass fraction of 50%.When GECPs concentration≥2.0%,the emulsions were O/W/O type,and at higher GECPs concentration（≥4%）,the emulsion was very stable with inner oil droplets（3.3～4.0μm）and outer water droplets（20.6μm～24.1μm）remained unchanged even after60 days of storage.Besides dodecane,double structures can also be obtained when using other common oils as the oil phase.After the enzyme was loaded into the double emulsion,the catalytic reaction rate of lipase was greatly accelerated,the substrate conversion rate reached80.9%after 15 min,and the catalytic activity remained at least 97.4%in 10 cycles.In addition,using the Pickering double O/W/O emulsification system as a template,porous microspheres with controllable size can be obtained,which paved the way for the subsequent preparation of porous materials.4.To obtain protein-based hierarchical porous materials with excellent mechanical properties,adjustable pore structure,and biodegradability,emulsion stabilized by gliadin-chitosan hybrid particles（GCHPs）was used as the pore-forming template,gelatin as the gel-forming matrix,and kosmotropic ions in Hofmeister series as the physical cross-linking agent.By strengthening the continuous phase structure,protein-based hierarchically porous materials with favorable mechanical strength,biodegradability and controllable pore structure were obtained here.Mercury intrusion porosimetry analysis showed that the average pore size of the hierarchically porous materials was around 20μm,and the pore size showed a multimodal distribution,the pore structure and porosity can be adjusted by by altering the mass ratio of hexane or gelatin in the emulsion-gel template.The Hofmeister effect resulted from kosmotropic ions greatly enhanced the Young’s modulus and the compressive stress at 40%strain of porous materials from 0.56 to 6.84 MPa and 0.26 to 1.11 MPa,respectively.The protein-based porous material exhibited excellent fluid absorption and deformation resistance,these materials were also nontoxic to Ha Ca T cells.Strength of the material increased with the concentration of（NH₄）₂SO₄,and the other four kosmotropic salts,Na₂S₂O₃,Na₂CO₃,Na H₂PO₄and Na₂SO₄ also showed similar positive effects.5.Based on the previous chapter,efforts were made to develop a more green and natural preparation method for porous materials,thus avoiding the use of organic solvents.The method used gliadin particles（GPs）as stabilizers for the air-water interface to provide Pickering stabilization,gellan gum（GG）was used for the formation of the network in the continuous phase,and Ca²⁺as cationic gel enhancer.The synergistic stabilization of GPs and GG in the wet foam highly limited the destabilization phenomena of bubbles such as drainage,coarsening,flocculation,and disproportionation.By using wet foam as a template,the feasible preparation of the porous materials was achieved by removal of the water in wet foam through the freeze-drying process,besides,the dried foams obtained here were micron-sized porous materials with porosities of 84.3-93.4%,and average pore sizes of 5.0-156.9μm,also their average pore diameter can be changed easily by altering the GPs/GG concentrations.In addition,these porous materials had high porosity,micron-scale pore structure,and exhibited good performance in vitro biocompatibility,mechanical properties,and water absorption capacity,more importantly,their highly open and interconnected pore structure facilitated the growth and proliferation of Ha Ca T cells on the porous materials.