Fabrication And Stability Mechanism Of Pickering Emulsions Based On Dihydromyricetin

Pickering emulsions are the emulsions stabilized by solid particles instead of surfactants.Compared with the traditional emulsions,Pickering emulsions have the advantages of irreversible interfacial adsorption and excellent anti-coalescence stability.For foods and medicines,food-derived protein and polysaccharide particles are expected to be superior to inorganic or organic synthetic polymer particles in terms of cost,biocompatibility,degradability and consumer acceptance.However,the preparation of protein and polysaccharide particles often includes the modification treatments such as organic solvent treatment,acidolysis,esterification and so on.These methods have some problems,such as tedious processing,environment pollution,uncertain product safety and so on.Fortunately,some food-derived flavonoids have been found to stabilize Pickering emulsions either alone or in conjunction with biological macromolecules.The fabrication of the corresponding emulsions based on flavonoids can not only expand the source of Pickering emulsifiers,but also endow the emulsions with new biological functions.Dihydromyricetin(DMY)is the main flavonoid of Ampelopsis grossedentata leaves with many bioactivities.Our preliminary study accidentally found that DMY particles could reside at the oil-water interface and stabilize Pickering emulsions,but the relevant mechanism was unknown.In this study,DMY,its complexes and mixtures with food-derived biopolymers were developed as the simple,green,low-cost and controllable particle emusifiers,and the corresponding Pickering emulsions were also established.The effects of particle properties and environmental factors controlling the structure and properties of Pickering emulsions were systemactically investigated by means of microscope,rheology,texture and spectrum.Based on the above experiments and theoretical calculations,the multi-scale correlation of “molecular interaction-interface behavior-particle characteristics-emulsion properties” was established to clarify the underlying formation and stability mechanism.The main contents and results are as follows:(1)The food-grade Pickering emulsion gels stabilized by DMY were constructed.The properties of DMY particles,the factors affecting the gel formation,the microstructure and mechanical properties of the gels developed under different conditions were investigated respectively.The results indicated that DMY particles were the rod-like crystals with amphiphilicity,which could overlap each other to form a three-dimensional space network,acting as a physical barrier to separate the oil-water phase and stabilize the emulsion gels.The concentration of DMY and the mass fraction of oil phase had significant effects on the formation and mechanical properties of the gels,and the alkaline and low ionic strength conditions were beneficial to the stability of the gels.(2)To clarify the molecular mechanism of DMY stabilizing Pickering emulsions.The flavonoids with similar structures(DMY,myricetin and myricetrin)were selected to systematically compare their Pickering emulsifying ability,chemical structure parameter,and interfacial tension,and their dynamic adsorption behavior at oil-water interface was studied by molecular dynamics method.The results suggested that both DMY and myricetirn could stabilize Pickering emulsions,and DMY tended to stabilize the gels.Myricetin was difficult to stabilize Pickering emulsions for its poor emulsifying capacity.Pickering emulsifying capacity may be closely related to log P value and dipole moment.Molecular dynamics analysis exhibited that DMY,myricetin and myricetrin could all reside on the oil-water interface and increase the interfacial thickness.Myricetrin had the best effect on reducing interfacial tension,while myricetin had the worst ability to reduce interfacial tension,which was consistent with the actual experimental results.The radial distribution function could better reflect the molecular orientation and aggregation of these flavonoids at the oil-water interface,which could be used as a potential index to predict the ability of flavonoids to stabilize Pickering emulsion.(3)A practical green strategy for preparing Pickering emulsion gel with DMY/high-amylose starch(HCS)composite particles was established,whose stability mechanism was clarified based on the experimental and theoretical methods.It was found that the DMY content in composite particles and the addition amount of composite particles had obvious synergistic effect on the formation and properties of emulsion gels.The obtained emulsion gels were not sensitive to ionic strength.The spectral analysis confirmed the presence of DMY/HCS supramolecules.The molecular simulation of the supramolecular complexes in the oil-water system indicated that these complexes could spontaneously aggregate and anchor to the oil-water interface,reducing the interfacial tension.(4)With DMY/HCS composite particles as emulsifier,Pickering nano-emulsions were constructed by combining high-speed shear and high-pressure homogenization.The effects of particle properties and homogenization conditions on the formation and delivery properties of Pickering nano-emulsions were investigated systematically.The results showed that the composite particles and homogenization conditions had a significant effect on the droplet size of the emulsions,and the composite particles with the DMY content of 5-20% could stabilize Pickering nano-emulsions.The oil phase of the obtained emulsions possessed good stability during high-temperature storage,and their β-carotene protecting performance against UV irradiation was also superior to that of the nano-emulsion stabilized by Tween 20.The in vitro simulated digestion test also indicated that the nano-emulsions developed by composite particles could significantly improve the bioaccessibility of β-carotene and had the potential to reduce blood sugar.(5)The feasibility to construct food-grade Pickering high internal phase emulsion(HIPE)gels directly by using the mixture of lysozyme(LY)and DMY was evaluated.The effects of the composition and amount of the mixture and the volume fraction of oil phase on the structure and properties of HIPE gels were investigated.Then,the formation mechanism of HIPE gels was also revealed based on the experimental and molecular simulation methods.The results showed that DMY and LY could stabilize HIPE gels at lower concentration,and DMY played a leading role in the formation of HIPE gels.In this process,DMY had no significant effect on the activity of LY,and the interaction between LY and DMY was weak.The existence of LY contributed to the further reduction of the interfacial tension of oil-water system.Molecular simulation also confirmed that it was difficult for DMY to enter the active site of LY to form a classic host-guest supramolecular complex,and DMY could stabilize the emulsion by overlapping with LY.In addition,the obtained HIPE gels had excellent performance in protecting lutein and inhibiting oil oxidation.