Study On The Mechanism Of Oil-water Interface Self-assembly Behavior Of Linear Dextrin Nanoparticles

Pickering emulsion is a new emulsion which consists of solid particles instead of traditional surfactants.Solid particles adsorb at the oil-water interface to form a physical barrier that prevents droplets from aggregating.In recent years,starch has become one of the important raw materials to meet the requirements of biology,medicine and food because of its biocompatibility,wide sources and low cost,and has attracted extensive attention in the preparation of Pickering emulsion.Linear dextrin（LD）,as a starch derivative,is a linear molecule obtained by enzymolysis of amylase and composed ofα-1,4-glucosidic units.LD has great potential in stabilizing Pickering emulsion and delivering functional components.However,there are few studies on LD particles as Pickering emulsion stabilizer.In this thesis high amylose corn starch was used as raw material,and LD with different chain lengths were obtained by purification of amylose,enzymolysis ofα-amylase,and then gradually graded.The properties and interface behaviors of LD were characterized,and Pickering emulsion was prepared with LD nanoparticles with different chain lengths as stabilizer.The emulsion was measured by microscopy,rheometer,antioxidant,and in vitro simulated digestion,etc.The emulsification properties of LD with different chain lengths were explored,and the mechanism of LD stabilizing Pickering emulsion with different chain lengths was revealed.The main research results are as follows:（1）A new method for the separation and purification of amylose by recrystallization of n-butanol from high amylose corn starch with calcium chloride solution was established.The purity,yield,crystallization structure and gelatinization temperature of amylose were compared with that of amylose purified by traditional sodium hydroxide solution.The extraction yield of amylose purified with calcium chloride solution（55.42±0.53%）was slightly lower than that of amylose purified with sodium hydroxide solution（61.17±0.60%）,but its purity was higher.The consumption of reagent solution is only about 30%of sodium hydroxide,which improves the overall preparation efficiency of amylose.XRD and DSC results showed that amylose extracted by calcium chloride solution had more ordered and compact structure.（2）A group of LD with different chain lengths was prepared byα-amylase enzymatic hydrolysis of amylose.Three kinds of LD nanoparticles with average chain length（ACL）of23,27 and 32 were obtained by gradual dissolution and classification of amylose after enzymatic hydrolysis,which were named LD-F₁,LD-F₂and LD-F₃,respectively.LD-F₁forms the smallest particle size,and samples containing LD components with longer chains are more likely to fold and curl each other to form larger particle sizes.The adsorption kinetics results show that the shorter the chain length of LD,the higher the diffusion rate constant(k_diff)and permeability constant(k_pen),and the lower the rearrangement rate constant(k_rea).LD molecules containing more short chains have higher amphiphilicity and lower migration resistance near the oil-water interface,so they can migrate to the oil-water interface more quickly,penetrate the single layer of the interface more easily,and accumulate more on the interface.（3）LD nanoparticles with different chain length distributions can form Pickering emulsion with good stability.LD particles with different chain lengths showed different emulsifying ability with the increase of emulsion time.The order of storage stability of LD stabilized emulsion is F₃emulsion<F₂emulsion<F₁emulsion,emulsion index is 3.16±1.05%,19.00±0.83%,23.33±2.18%,respectively.Reducing the chain length of LD is helpful to improve its emulsifying property.The emulsion droplet image and droplet size observed by optical microscope show that the emulsion droplet formed by short chain LD is smaller and denser than that formed by long chain LD.With the increase of LD chain length,the average diameter of emulsion drops increases from 3.93μm and 4.77μm to 5.13μm.Fluorescence microscope images showed a layer of dense LD solid particles adsorbed around the oil droplets.（4）The rheological results showed that the viscosity of emulsions decreased with the increase of LD chain length,and all showed shear thinning characteristics.The energy storage modulus（G’）of the emulsion is greater than the loss modulus（G"）,and the values of G’and G"decrease with the increase of LD chain length.The simulated digestion experiments of the emulsion prepared by LD-F₁,LD-F₂and LD-F₃showed that the release rate of free fatty acids in the emulsion prepared by long chain LD was faster and higher.Within 30 minutes before digestion,the content of free fatty acids in all samples increased rapidly and could be hydrolyzed rapidly.After 2 hours of digestion,the fatty acid release rates were 76.19±2.1%,82.27±3.4%and 91.35±2.9%,respectively.The antioxidant activity of Pickering emulsion prepared by LD-F₁was the strongest,and the content of malondialdehyde in the emulsion was only 20.6 mmol/kg.Compared with LD containing longer chain,LD with short chain is more easily adsorbed on the oil-water interface and has a higher filling capacity,forming a thicker interface layer around the oil droplet,which effectively inhibits the penetration of pro-oxidant and thus delays the oxidation rate of lipid.