Fabrication And Functionality Delivery Of Food Grade Water-in-water (W/W) Emulsion

Food is regarded as the complex material containing multiple components in multiscale hierarchical structure.Protein and polysaccharides are two kinds of biomolecules that are commonly found in foods.Due to thermodynamic incompatibility,these two biopolymers tend to separate from each other and therefore,turn to be an aqueous two-phase system(ATPS).This thesis focuses on the structural design and fabrication strategies of stable water-in-water(W/W)emulsion,and its application in functionality delivery.Based on the theory of structure design,we can manipulate the microstructure of W/W emulsion in two dimensional(W/W interface)and three dimensional scale(bulk stereostructure).The mechanism of stabilization of W/W Pickering emulsion and multiple W/W/W emulsion had been clarified in this work.By mapping the relationship between its microstructure and physiochemical properties,structured W/W emulsions with specific functionalities could be prepared.(1)When compared to traditional oil/water emulsions,the interface between two hydrophilic biopolymer phases is ill-defined,and the interfacial tension is extremely low.As a result,typical emulsifiers are hard to adsorb at W/W interfaces.A food grade W/W Pickering emulsion was prepared with zein-pectin complex particles(ZP).Due to the fact that polysaccharides could modify the functional properties of protein particles,here,different ratios of zein and pectin was used to prepared zein-pectin complex particles(ZP).The wetting property of ZP particles in the mixed system of waxy corn starch(WCS)and guar gum(GG)could be manipulated simply by tuning the complex ratio of zein and pectin.Once ZP particles obtained with proper wetting property,they could absorb to the WCS/GG interface and therefore,stabilized the WCS/GG Pickering emulsion.The analysis of digestibility curves indicated that this structured W/W Pickering emulsion was effective in inhibiting the contact of WCS and amylase and slowing down starch digestion.(2)The significant differences in the solubilities of bioactives in the two solvents with distinct polar attributes made the oil/water emulsion a good loading vehicle for bioactives.However,this might be only suitable for loading hydrophobic components.Based on the zein-particle stabilized W/W emulsion system,and the affinity differences of riboflavin in two incompatible biopolymers,an edible W/W Pickering emulsion was prepared for loading hydrophilic bioactives.Soy protein isolate(SPI)and GG were used to prepare the aqueous two-phase system.By manipulating the interaction between hydrophilic bioactive substance(riboflavin)to SPI and GG,the preference of the bioactive to these two components of the aqueous mixed system could be tuned.With the significant preferential difference,the hydrophilic bioactive substance could be facilely induced to load in the targeted droplets of the ZP stabilized SPI/GG Pickering emulsion.As a result,the ZP stabilized SPI/GG Pickering emulsion was prepared and served as an effective vehicle to deliver the hydrophilic bioactive substances.(3)A facile approach for fabricating gelatin@zein edible protein-based microsphere with a W/W emulsion template were proposed.Gelatin and dextran were used to prepare aqueous two-phase system.Sodium alginate(Alg)was used to induce zein to be absorbed at the W/W interface.Followed to cross-link by Ca²⁺,gelatin microspheres with a relatively hydrophobic particle shell were constructed.This structured hydrophobic shell could hinder the transmission of water molecules between two phases and reinforce the mechanical property of gelatin microspheres.As a result,these core-shell gelatin microspheres showed excellent stability in different temperature(up to 60°C),p H(p H 2.0-7.0),salt concentration(0-400 m M)and ageing(over 1 month).All of these advantages provide these gelatin@zein microspheres great potential to apply in functionality delivery.(4)Gelatin was introduced as the third phase to stabilize the binary system of starch and guar gum.Due to the aggregation behavior of gelatin in low temperature and its incompatibility with the other two polymers,multiple water-in-water-in-water(W/W/W)emulsions of starch/gelatin/guar and guar/gelatin/starch were prepared.The effects of temperature,p H and gelatin amount on the formation and microstructure of the resultant emulsion had been investigated.The results indicated that reducing temperature could induce self-assembly of gelatin molecules,the thermodynamic property of the obtained gelatin aggregates in the aqueous starch and guar gum was changed,from thermal compatible to incompatible.Through manipulating their phase behavior in these three-components mixed system,the multiple W/W/W emulsions of starch/gelatin/guar and guar/gelatin/starch were produced.(5)Based on the formation mechanism of the W/W/W emulsion,the effect of gelatin concentration,p H and temperature to the structure of the multiple W/W/W emulsions of starch/gelatin/guar and guar/gelatin/starch during ageing was investigated.Based on the relationship of their microstructure,viscosity and stability,it was claimed that the stability of these multiple W/W/W emulsions were attributed to the absorption of gelatin domains between starch and guar gum phases.By adding more than 0.5 wt%gelatin,emulsions of GG droplets in a continuous WCS phase or vice versa could be stabilized between p H 4.5 and p H 5.0 for a period of at least one week at temperature less than 30°C.This might provide a new strategy for stabilizing W/W emulsion and fabricating complicated structure in food.