| Pickering emulsion,as a type of emulsion stabilized by solid particles,confers strong stability against coalescence.It has been attracting considerable research in the food industry since it can be used to transport nutrients compared with inorganic particles e.g.,silica,the particles prepared by food-grade materials are natural,green,safe and non-toxic.As an essential nutrient for the human body,therefore,food-grade dietary fat was selected as the basic material to prepare Pickering solid particles in this paper.However,the research on the Pickering emulsion stabilized by dietary fat solid particles is still lacking.What's more,the mechanism of how solid lipid particles' structure affects their interfacial properties and the resulting stability of Pickering emulsion stabilized by dietary fat is still unclear.Therefore,in this thesis,fully hydrogenated soybean oil(FHSO)is used as dietary fat to fabricate SLPs with different crystalline structures and interfacial properties by changing the processing conditions(ultrasonic power and time),the type of emulsifiers(Tween 40(T40),sodium caseinate(Na-Cas)),and the addition amount(0-6 wt.%)of emulsifiers,then these SLPs were applied to prepare Pickering emulsions.On this basis,we analyzed the interfacial adsorption and assembly behavior of SLPs and clarified the relationship among the crystalline structure of SLPs,the interfacial properties and the stability of Pickering emulsion,which could provide guidance for the preparation and application of fat-based Pickering emulsion.The main research contents and results are as follows:1.Research on the structural properties of SLPs and storage stability of emulsion prepared under different ultrasonic treatment conditionsSLPs with different particle sizes,crystal forms and morphologies were prepared by changing the ultrasonic treatment conditions(power: 300-450 W;time: 1-6 min),then the influence of these SLPs on emulsion stability was studied.Results showed that the Z-average of T40-SLPs were ranging from 259 to 480 nm,moreover,the crystal exhibited both ? and ? polymorph with rod-like and irregular spherical shape.T40-SLPs with different particle sizes,crystal form,and morphologies can be used to fabricate stable Pickering emulsions.The increased irregular spherical ?-form particles in emulsions prepared with T40-SLPs increased their creaming indexes after storage for 14 d and led to emulsion destabilization.The results indicated that the crystal form and morphology of SLPs had a greater impact on the storage stability of the Pickering emulsion.2.Study on the properties of SLPs prepared with different types and concentrations of emulsifiersSLPs with different crystal structures were prepared by adding 0.5-6 wt.% T40 or Na-Cas.The effects of emulsifier types and concentrations on the particle size,surface wettability,morphology,crystal form and emulsification ability of SLPs were explored.Results showed that the Z-average of SLPs with different concentrations of T40 were ranging from 136 to 373 nm.When T40 content was low(0.5 wt.%),SLPs exhibited both ? and ? form with small plate-like and spherical shape.As T40 content increased,the Z-average sizes of SLPs decreased significantly,whereas the ? form plate-like crystals and the hydrophilicity of the particles gradually increased.While,the Zaverage of the Na-Cas-SLPs were ranging from 324 to 485 nm.In addition,Na-CasSLPs were spherical and had ? polymorph.With increasing concentrations of Na-Cas,the Z-average sizes and hydrophilicity of SLPs decreased and increased,respectively.Although SLPs containing 0.5 wt.% T40 or 0.5wt.% Na-Cas could not form stable emulsions,both T40-SLPs and Na-Cas-SLPs could not form stable emulsions,both T40-SLPs and Na-Cas-SLPs consisting of 1-6 wt.% emulsifier can form stable Pickering emulsions and emulsions prepared with T40-SLPs and Na-Cas-SLPs had smaller droplets,multilayer adsorption interfaces,and thicker interface film and crystalline layers with the increase of the emulsifier concentration.Compared with the emulsion stabilized by T40-SLPs,the emulsion stabilized by Na-Cas-SLPs had a smaller droplet size,a larger zeta-potential value,a thinner interface film and crystalline layer,and a stronger storage stability.3.Study on the adsorption and assembly behavior of emulsifier on the surface of SLPs and the adsorption behavior of SLPs at the oil-water interfaceThe mechanisms of T40-SLPs and Na-Cas-SLPs improved the stability of Pickering emulsions were explored based on the interfacial adsorption percentage of the emulsifier and the adsorption and assembly behavior of SLPs at the oil-water interface.Results showed that the interfacial adsorption concentration gradually increased with the increasing content of the emulsifier.During preparation of SLPs,T40 molecule of T40-SLPs participated in the fat crystallization of the oil phase,hence causing changes in the morphology and crystal form of the SLPs.As the amount of T40 increased from0.5 wt.% to 6 wt.%,the emulsifier adsorption layer was more densely packed with increased thickness,resulting in its improved surface wettability.For Na-Cas-SLPs,NaCas was adsorbed on the SLPs surface via intermolecular interactions,therefore it did not participate in the crystallization of the oil phase,and the increase in the interfacial protein load decreased the droplet size but increased the thickness and density of the adsorption layer.The adsorption behavior of SLPs at the oil-water interface revealed that both T40-SLPs and Na-Cas-SLPs can form interfacial films through adsorbing at the oil-water interface.Both T40-SLPs and Na-Cas-SLPs with different emulsifier concentrations were strongly adsorbed at the oil-water interface except the SLP prepared with 1 wt.% T40,thus they were not easy to desorb from the oil-water interface.These results were consistent with the results of emulsions' storage stability.4.Effects of particle concentration and oil phase content on the properties of SLPsstabilized Pickering emulsion.Effects of particle concentration and oil phase content on the stability,microstructure,and rheological properties of Pickering emulsions constructed with T40-SLPs and NaCas-SLPs were studied.Results showed that both T40-SLPs and Na-Cas-SLPs can stabilize Pickering emulsions with different added concentrations(0.8,1,and 1.2 wt.%).Moreover,increasing the concentration of T40-SLPs and Na-Cas-SLPs from 0.8 wt.%to 1.2 wt.% did not significantly change the droplet size and zeta potential of the emulsion but increased the thickness of the interfacial crystalline layer and the viscosity of the emulsion.Additionally,all emulsions had good storage stability during the 14-d storage period.When the SLPs concentration was constant(1 wt.%),stable Pickering emulsions can be prepared with T40-SLPs and Na-Cas-SLPs and this was not affected by the oil phase content.Increasing the oil phase content from 10 wt.% to 30 wt.%significantly increased and decreased the average droplet size of the emulsion and the thickness of the interfacial film and crystal layer,respectively.During 14-d storage period,emulsions prepared with T40-SLPs and Na-Cas-SLPs with 10 wt.% and 20 wt.%oil phase content kept stable,however,this was not the case for the emulsions stabilized with T40-SLPs containing 30 wt.% oil phase content. |
PDF Full Text Request