| Pickering emulsion is a kind of emulsion stabilized by particles instead of traditional emulsifiers with strong stability and high added value.Pickering emulsions stabilized by food-grade particles have been developed.In recent years,some common food grade particles have been developed to stabilize Pickering emulsion.China is the largest producer of peanuts in the world,has abundant peanut protein resources with high nutritional value and strong functionality.However,peanut protein has not been developed into Pickering emulsifier yet.It is of great significance to develop a Pickering emulsion with peanut protein as raw material and explore its stability mechanism.1.The rheological properties of peanut protein isolate(PPI)and three different charged types of polysaccharides,chitosan(CS),guar gum(GG)and xanthan gum(XG),in a single system and blended system were studied.The results of continuous shear tests of single and blended systems are in accordance with Power law model(R~2?0.992).High-pressure homogenization delayed the gelation time of PPI and PPI+GG systems by destroying the initial gel network structure.2.Four microgel particles,PPI,PPI+CS,PPI+GG and PPI+XG were prepared by gel-crushing method.The size and zeta potential of the particles were measured.Cryo-SEM microscopic observations were used to characterize the structure of the emulsions.The results showed that the particle size was between 174.57±1.19~195.9±0.75 nm and the potential ranged from(-)35.57±0.67 to(-)43.5±0.92.The microgel particles showed an irregular rod-like structure.3.The Pickering emulsion was stabilized using the above prepared PPI and the three PPI-polysaccharide composite gel particles.The stability and microstructure of the emulsion were studied placing the samples at ambient temperature and Cryo-SEM and CLSM characterization;besides,the stability mechanism of emulsion was discussed.The results showed that the particle concentration influences the anti-coalescence stability of Pickering emulsion.When the particle concentration is low(0.2%),coalescence destabilization occurs among the droplets.The creaming index of Pickering emulsion index is relevant to oil mass fraction,correlation coefficient of the emulsions was between 0.9886 and0.9987.Four emulsion systems were stable at room temperature for at least 30 days.The microstructural characterization showed that the Pickering emulsion is stabilized by the particle layer and the gel network structure formed by the microgel particles adsorbed on the oil-water surface as well as in the continuous phase.4.The mechanism for how external environment(ionic strength,pH)adjust the properties of PPI microgels such as potential,particle size,three-phase contact angle,and aggregation morphology were explored.The results showed that with the increase of ionic strength,the absolute value of zeta potential of PPI microgel particles decreased rapidly due to the electrostatic shielding effect.PPI microgel particles were aggregated due to reducing of electrostatic repulsion which resulting the particle size increased.When the pH was farther away from the isoelectric point,the PPI microgel particles increased are easier wetted by water,and the swelling of particles made the size larger;the three-phase contact angle of PPI microgel particles near the isoelectric point of the protein(pH=4.5)was the highest(156°for edible oil,n-hexane for 132°),which means the particles are easier wetted by oil.The contact angle of the particle decreases with the pH away from the isoelectric point,and the hydrophilicity of the PPI microgel particles increases.The cryo-SEM image shows the aggregate state of PPI microgel varies with pH.5.PPI microgel particles were used to stabilize high internal phase Pickering emulsions(HIPPEs).The emulsion structure was characterized by Cryo-SEM and CLSM.The results showed that the HIPPEs with an internal ratio of 85%can be prepared when the pH of the particles was adjusted to 3.0 and 9.0;the particles tightly covered around the deformed droplets,preventing the coalescence between the droplets;the network structure formed by particles in continuous phase blocked the contact between the droplets;the degree of aggregation of the particles determined the structure of the emulsion,and the droplet size(5-50?m)of the particle-stabilized HIPPEs at pH 3.0 was greater than that at pH 9.0(1-20?m).At pH 9.0,HIPPEs with a maximum oil mas fraction of 87%can be stabilized.This ratio is currently highest in food-grade Pickering emulsions.6.PPI microgel particle-stabilized HIPPEs with hexane as the internal phase were prepared,the protein-based porous material was successfully prepared using the high-internal Pickering emulsion as a template.The structure of the emulsion and the relationship between the emulsion and the porous material were studied.The results showed that the particles in the emulsion formed a porous material wall after drying the emulsion.The evaporation of n-hexane promoted the formation of pores;the thickness and toughness of the material wall can be adjusted by changing the concentration of PPI microgel particle.When the particle concentration was higher(1.5 and 1.83 wt.%),a tougher uniform material wall can be obtained.7.By comparing the rheological properties of HIPPEs with commercially available margarine and salad dressings,the application of HIPPEs in foods was explored.The results showed that the stable HIPPEs of PPI microgel particles at pH 3 and pH 9 are similar in shear thinning properties of different brands of margarine,besides their shear thinning properties can be performed according to target requirements.Both HIPPEs and salad dressings showed similar shear rheological properties and do not have frequency dependence.8.The prepared HIPPEs were used to load trans-resveratrol and polydatin,and the protective effect of the carrier on photosensitivity was examined.The results showed that the PPI microgel particles stabilized high-phase internal Pickering emulsion system can effectively reduce the loss of trans-resveratrol and polydatin glycosides under UV exposure.The content of resveratrol decreased rapidly by80.5%,and the irradiation time was extended to 90 minutes.The content of resveratrol in the system was reduced by 88.4%,while the content of trans-resveratrol loaded by HIPPE was almost unchanged.The content of edible oil loaded with trans-resveratrol glycosides decreased by 88.1%after 90 min UV exposure.When HIPPE loading was used as the delivery system under the same exposure conditions,the reduction of trans-resveratrol glycoside was only 30.1%. |
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