| As a natural biopolymer widely studied at present,nanocellulose shows some excellent properties of macro-cellulose and nanomaterials,such as renewability,excellent mechanical properties,low thermal expansion coefficient,easy modification and environmental friendliness.In addition,due to its natural amphiphilicity and high aspect ratio,the nanocellulose stabilized Pickering emulsions has also received increasing attention.The application of nanocellulose in stabilizing emulsion is mainly related to its morphology,structure and hydrophilic/hydrophobic properties.Generally,the cellulose nanocrystals with shorter size are more rigid and can be closely adsorbed on the surface of droplets in the process of stabilizing emulsion,thus showing a good stability of emulsion.The longer cellulose nanofibrils are more flexible and mainly distribute in the aqueous phase in a three-dimensional network structure,and the emulsion stability was relatively weak.Traditionally,cellulose nanocrystals are usually prepared by sulfuric acid hydrolysis,but the reaction is miscellaneous and produce a lot of acidizing waste water.Cellulose nanofibrils are mainly prepared by mechanically assisted method with a high yield and simple operation,which can meet the concept of green and sustainable development,thus showing more promising development prospect in stabilizing Pickering emulsions.Due to the strong hydrophilicity of nanocellulose,the research of nanocellulose as emulsified particles mainly focused on the single type of chemical modification treatment or the co-stabilization emulsion with other nanoparticles.However,there is little information in Pickering emulsion co-stabilized by different types of natural unmodified nanocellulose(such as cellulose nanocrystals and cellulose nanofibrils).The strong rigidity of cellulose nanocrystals and flexible prominent cellulose nanofibrils can realize the complementary advantages,make up make up for their shortcomings in the application of Pickering emulsions,and broaden the green application of nanocellulose stablized emulsions.This research developed full utilization of agricultural product processing waste resources,used lemon seed residue after oil extraction as raw material to extract cellulose.Then,the lemon cellulose nanofibrils(LSCNF)was obtained by ionic liquid combined with ball milling method,and the lemon seed cellulose nanocrystals(LSCNC)was isolated by traditional sulfuric acid hydrolysis method for co-stabilizing Pickering emulsions.The stabilization mechanism of Pickering emulsion was revealed through the analysis of the emulsion structure and stability,,and the application potential of Pickering emulsion in curcumin embedding was further explored.In this study,the green and efficient approach of ionic liquid-ball milling method was used to enrich the high value of lemon processing waste utilization ways,and different types of natural nanocellulose(LSCNF and LSCNC)were used to construct green friendly Pickering emulsions.The adjustability of LSCNF to the properties of Pickering emulsion was emphasized,which was helpful to enrich the co-stabilization mechanism of emulsion by different types of unmodified nanocellulose and the related applications.The main contents and results are as follows:(1)The lemon seed cellulose nanofibrils(LSCNF)were prepared by mechanical ball milling methods using lemon seeds as raw materials and ionic liquid1-butyl-3-methylimidazolium chloride([BMIM]Cl)with different mass fractions(0-50%)as wet grinding medium,.The results showed that the addition of [BMIM]Cl could regulate the morphology and structure of LSCNF during ball milling.With the increase of [BMIM]Cl mass fraction,the length of LSCNF gradually became smaller and the diameter gradually became larger.When [BMIM]Cl mass fraction was 50%,the length of LSCNF was the smallest(500-600 nm),but the diameter was relatively large(40-60 nm).The XRD and FTIR results showed that all the obtained LSCNF were cellulose I? crystal form,and the addition of [BMIM]Cl reduced the degree of crystallinity reduction of LSCNF.The results of thermogravimetric analysis showed that the residual mass fraction of LSCNF prepared by ionic liquid-ball milling method was similar to that of lemon seed cellulose,but both were higher than that of LSCNF prepared by ball milling only.The rheological analysis results showed that LSCNF suspensions were all non-Newtonian fluids,and the relative viscosity of LSCNF with longer length was higher at a contant shear rate.The green method combining ionic liquid and ball milling can efficiently prepare LSCNF from lemon seeds and retain the original cellulose crystal form.The increase in [BMIM]Cl addition is beneficial to improve the crystallinity and thermal stability of LSCNF.The morphology and performance of LSCNF can be adjusted and coontrolled by the mass fraction of ionic liquid during ball miling.(2)The LSCNF obtained by the ionic liquid-ball milling method and LSCNC prepared by the sulfuric acid hydrolysis method were used as nanoparticle emulsifiers to synergistically stabilize Pickering emulsion.The effects of the ratio of LSCNF/LSCNC and the concentration of LSCNF on the properties of Pickering emulsion were systematically investigated and compared.The synergistical stabilization mechanism of emulsion was revealed through the emulsion microstructure,stability analysis and environmental factors analysis The results showed that the shorter LSCNC achieved irreversible adsorption at the oil/water interface,while the longer LSCNF formed bridges between adjacent emulsion droplets to form a three-dimensional network structure,which effectively improved the viscoelasticity of the emulsion.At the same time,the introduction of LSCNF endowed the prepared Pickering emulsion with a better storage stability and adjustability.In addition,due to the synergistic effect of LSCNC and LSCNF,the stability of the emulsion under different ionic strength and pH were also improved,and Pickering emulsion can also be formed at low pH(> 4)or low ionic strength(<20 m M).(3)The LSCNC/LSCNF synergistically stablized Pickering emulsion was used as a delivery system to encapsulate lipophilic curcumin on the stability of the emulsion and the protective effect of curcumin.The results showed that the physical stability of the emulsion containing curcumin still remained good after 15 days storage,and its rheological properties were slightly enhanced compared with the emulsion without curcumin,promoting the stability of the emulsion.The curcumin embedded in the emulsion was beneficial to alleviate its natural degradation and increase its retention rate.The retention rate of curcumin was greatly affected by storage temperature,and the retention rate at low temperature(4 ?)was significantly better than that at slightly higher temperature(25 ?).After 30 days of storage,the curcumin retention rate of the emulsion with the highest LSCNF concentration(1%Cur)exceeded 75%,while the retention rate of the control sample with only dissolved by sunflower oil was less than 50%.The in vitro simulated digestion of the curcumin Pickering emulsion showed that more nanocellulose particles not only formed a dense cover around the oil droplets,but also formed a three-dimensional network structure in the water phase,which can inhibit the enzymatic hydrolysis of the oil droplets by lipase to a certain extent,and slow down the release of free fatty acids,which is conducive to research on the delivery of sustained-release biologically active substances. |
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