Preparation Of Starch Nanoparticles By Anti-solvent Method And Its Application

Nanostarch is defined as starch particles or crystals with nanoscale,which can be achieved by modification of native starch.Compared with native starch,nanostarch has high adsorption capacity,excellent solubility and bioavailability,and has significant application advantages.The preparation of starch nanoparticles(SNPs)by anti-solvent method is to fully gelatinize the native starch firstly,and then anti-solvent drives the supersaturation of starch molecules in the system to form SNPs.At present,the reports regarding antisolvent synthesis of SNPs lack in-depth exploration of growth mechanism of amylose and amylopectin in antisolvent,as well as the core factors that dominates the size of SNPs during the antisolvent process.In addition,the nano-size effect of SNPs makes them have the potential to stabilize Pickering emulsions.However,previous studies have less concerned about the effects of the size and morphological structure of SNPs on their emulsifying ability.The correlation between the nanostructure of SNPs and their emulsion stability needs to be further analyzed.Based on this,in this study,corn starch(CS)and waxy corn starch(WS)were used as raw materials,ethanol was used as anti-solvent,and SNPs were rapidly prepared by high-speed shear synergistic anti-solvent precipitation technology,SNPs was then used as an emulsifier to stabilize Pickering emulsion.Firstly,the self-assembly mechanism of amylose and amylopectin was clarified by systematic comparative analysis of the crystal structure,microscopic morphology and physicochemical properties of corn starch nanoparticles(CS-SNPs)and waxy corn starch nanoparticles(WS-SNPs).The size and morphological structure changes of the prepared SNPs under high-speed shear were further characterized,and the particle size of SNPs measured after high-speed shear treatment was used as the characterization standard for the size of self-assembled SNPs.On this basis,high-speed shear was combined with anti-solvent technology to enhance the solvent/anti-solvent mixing efficiency during the preparation of SNPs,with solvent/anti-solvent mixing efficiency,solvent/anti-solvent ratio and native starch sol concentration as variables,to study the core factors that dominate the size of SNPs during the self-assembly process,and to optimize the size regulation strategy of SNPs.By exploring the change trend of the morphological structure of SNPs under high-speed shear and ultrasonic treatment,combined with the stability analysis of SNPs-based Pickering emulsion prepared by high-speed shear and ultrasonication,the structure effect between the nano-size effect of SNPs and its emulsion stability was revealed.relationship,and provide a reference for the potential application of SNPs.The main research results are listed as follows:(1)SNPs with a single particle size of 20-100 nm could be rapidly prepared by high-speed shear synergistic anti-solvent precipitation technology,and synthesized SNPs existed in the form of particle aggregates but had excellent nano-size effect.The self-assembled SNPs induced by antisolvent were all V-shaped crystals with relatively low long-range order,and had highly ordered V-shaped single-helix structures within a short period.Starch molecules could use anti-solvent molecules as scaffolds to build a V-shaped single-helix structure,and the V-shaped structure formed by amylose was more dense and ordered than that of amylopectin.(2)The mixing efficiency of solvent/anti-solvent was the core parameter for regulating the size of SNPs.Enhancing the solvent/anti-solvent mixing efficiency by high-speed shear at15,000 rpm could reduce the mean size of CS-SNPs and WS-SNPs to 97.98 and 95.97 nm,respectively.On the basis of enhancing the solvent/anti-solvent mixing efficiency,the mean size of SNPs prepared by reducing the amount of anti-solvent and the concentration of native starch sol were all between 78.10 and 141.64 nm.Facilitating efficient solvent/anti-solvent mixing could not only produce smaller-sized SNPs,but also increase the yield of SNPs.(3)Under high-speed shear and ultrasonication,the morphological structures of CS-SNPs and WS-SNPs had similar changing trends.The dispersibility of SNPs under low-intensity shear(5000 rpm)was poor,and there were a large number of SNPs aggregates larger than 500 nm existing in the aqueous phase.High-intensity shear(20000 rpm)could homogenize the SNPs into sol with a mean size of about 100 nm.SNPs treated with low-power ultrasonication(200 W and 400 W)partially swelled to form a cross-linked network structure of SNPs-starch molecule-bound water with a mean size of about 150 nm,while high-power ultrasonication(600 W and 800 W)would cause SNPs to dissolve due to excessive gelatinization.(4)With the increase of high-speed shear and ultrasonic intensity,the emulsifying ability of CS-SNPs and WS-SNPs had changed in a similar trend,the precise regulation of the size and morphological structure of SNPs can improve the stability of the emulsion.The droplet size of the granular SNPs-based Pickering emulsions prepared by high-speed shear were around300-500 nm,but cannot maintain long-term stability due to the weak V-type hydrophobic effect of SNPs.The droplet size of the swollen SNPs-based Pickering emulsions prepared by low-power ultrasonication(200 W and 400 W)were about 200 nm,and a strong physical barrier is built between the emulsion droplets through the cross-linked network structure of SNPs,which were still stable after 180 days of storage.High-power ultrasonication(600 W and 800 W)treatment can lead to excessive gelatinization of SNPs and loss of nano-size effect,decreasing the stability of the emulsion.