Modification Of Starch Nanocrystals And Its Application In Pickering Emulsion

With the rise of nanotechnology and the deepening of the concept of sustainable development,more and more people are turning their attention to the easy-to-obtain,high-modulus,degradable natural polysaccharide nanocrystals.Starch nanocrystals(SNC)are a kind of natural polysaccharides.People use acid hydrolysis or high-pressure homogenization to remove the amorphous areas of starch to obtain high modulus and high strength SNC.In recent years,it has been widely used as a "filler" of polymer with its unique sheet structure and excellent biological properties to produce polymer materials with high mechanical strength and excellent gas barrier properties,especially for the development of green biodegradable materials.Another interesting application of SNC is to use it as an emulsifier to prepare green Pickering emulsions.Pickering emulsion is a highly stable,low-cost,environmentally friendly emulsion.It uses solid particles to replace traditional surfactants to stabilize the two incompatible phase interfaces.Researchers have used starch and its derivatives to prepare highly stable emulsions,but the reported research mainly focused on the concentration of starch nanocrystals,system pH or system preparation technology and equipment.Systematic studies on nanocrystal preparation of emulsions are relatively weak.Moreover,as a natural material from different sources,starch particles have a wide range of particle size,and the polyhydroxyl on the surface makes it strongly hydrophilic,which is not conducive to the stability of the emulsion.Therefore,this paper uses SNC as emulsifier,and improves its hydrophilicity and hydrophobicity through chemical modification to obtain a highly stable emulsion.The relationship between the emulsification ability of SNC and the degree of modification was evaluated from the aspects of morphological change and rheological response,and the relationship between emulsion droplet morphology and viscoelasticity was discussed in detail,and the surface properties and properties of SNC were discussed by comparing different modification methods.In addition,the influence of SNC surface properties and particle morphology on the phase inversion of the emulsion system is also discussed.The specific research content of this topic is as follows:(1)Stabilize the Pickering emulsion of olive oil in water by starch nanocrystals(SNC).Using different shear flows,the rheological properties of the emulsion were studied from the aspects of SNC content and oil-water ratio,and the effect of the degree of SNC surface acetylation on the viscoelasticity of the emulsion was further discussed.Studies have found that after surface acetylation,the reduction of surface hydrophilicity of SNC and the enhancement of electrostatic repulsion during the emulsification process significantly improve the emulsification ability of acetylated SNC,and the size of emulsion droplets is smaller and the distribution is narrower.Compared with the stable emulsion of SNC,the modulus and viscosity of the stable emulsion of acetylated SNC increased by about two orders of magnitude,and even showed strong overshoot behavior during the flow of large amplitude oscillatory shear(LAOS).(2)SNC grafted with octenyl succinic anhydride(OSA)is used as an emulsifier to stabilize caprylic/capric triglyceride(GTCC)in water emulsions:The relationship between the morphology and viscoelasticity of the emulsion is studied from the particle load and the degree of substitution(DS),especially the relationship between the formation of droplet clusters and the nonlinear viscoelastic response.Studies have shown that when the particle concentration and the higher oil-water ratio are high,the emulsion droplets are closely packed to form clusters due to the dissipation and stability mechanism.SNC's unique disc mounting structure and its improved amphiphilicity after surface treatment are of great significance to the formation and evolution of droplet clusters.In different shear flow fields,the deformation and relaxation of these clusters lead to weak overshoot and strong thixotropy,which is conducive to the storage and application of GTCC in emulsions.Finally,the sensory physical and chemical evaluation of the emulsion system prepared by SNC and acylated SNC was carried out.(3)Acetylated SNC and cross-linked SNC are emulsifier-stabilized(dextran)DEX-(polyethylene glycol)PEG water-water system:From the point of view of particle concentration and water-to-water ratio,the influence of cross-linking degree and modification method on emulsion morphology and emulsion type was explored.Studies have shown that the particle aggregation structure caused by cross-linking is more conducive to the stability of the emulsion.Compared with cross-linked SNC stable emulsion,the synergistic effect of particle size,surface affinity for two-phase solution and system viscosity makes the acetylated SNC stable emulsion system have better stability and wider reverse phase.This provides meaningful guidance for the development of water-water emulsions in the food/cosmetic field.