The Research Of 4D Printing Based On Pickering Emulsion Fabricated By The Extracted-citrus Pectin

China’s citrus planting area and yield rank first in the world,with over ten million tons of citrus peel produced annually due to processing.Realizing the efficient utilization of citrus peel is of great significance for the healthy development of the citrus industry.Firstly,the emulsification behavior and emulsion stability of different kinds of citrus pectin were explored from the structural characteristics of citrus pectin in citrus peel residue.Secondly,the double wettability of citrus pectin for the construction of Pickering emulsions was improved via the modification withβ-cyclodextrin（β-CD）,and the printing properties of Pickering emulsions were explored.Finally,the 4D printing of Pickering emulsions under heat induction was realized by embedding p H-sensitive natural pigments based on Pickering emulsions.It provided a new idea for the development of personalized 4D printing food and a new way for the high-value utilization of citrus peel residue.The specific contents and results were as follows:（1）Research on the extraction and emulsification properties of different types of citrus pectin.The citrus tachibana pectin（CTP）,shaddock pectin（SP）,lemon pectin（LP）,and orange pectin（OP）were extracted from the peel of Jinqiu sugar orange,Pinghe red heart pomelo,Anyue lemon,and Gannan navel orange,and the molecular structure and emulsifying properties of four pectins were investigated.The results showed that there were significant differences in molecular weight（Mw）and polysaccharide composition among the four types of pectins.The emulsions prepared by LP and SP had smaller sizes and more uniform distribution respectively,showing better emulsification behavior and emulsion stability.It can be seen from the molecular structure of pectin that the emulsifying activity of the four pectins was provided by the hydrophobic groups（methyl ester group and protein residue）in the pectin structure.The OP possessed the fewest hydrophobic groups,indicating that the emulsifying behavior of OP was low.Moreover,four citrus pectin exhibited an ellipsoidal structure and aggregated in the solution,which was consistent with the molecular configuration simulation results.The steric hindrance provided by Rhamnogalacturonan I（RG I）and the electrostatic repulsion force provided by theζ-potential ensured the stability of the emulsion.However,it was found that the OP with richer RG I region（Rha/Gal A:0.40）didn’t exhibit superiority in emulsification stability,speculating that was related to the low branching degree of RG I region in OP（Gal+Ara）/Rha:2.36).（2）The printing properties of Pickering emulsions stabilized by theβ-cyclodextrin（β-CD）/citrus pectin complexes.Because of the high hydrophilicity and complex structure of the citrus pectins,the citrus pectins were modified withβ-CD（hydrophobic）to stabilize Pickering emulsion in this study.This part systematically investigated the structure and emulsification behavior ofβ-CD/citrus pectin complexes,and explored the storage stability and printing characteristics of Pickering emulsions fabricated byβ-CD/citrus pectin complexes under different formulations.Firstly,the morphological features,emulsification behavior,and the relationship betweenβ-CD and citrus pectin of the citrus pectin modified withβ-CD were explored.Moreover,the printability and printing accuracy of Pickering emulsions were evaluated from the printing of a two-dimensional（2D）grid model and a three-dimensional（3D）hollow square cylinder model.The results indicated that the combination ofβ-CD and citrus pectin not only improved the dual wettability of the complexes（91.14±0.14°-109.43±0.22°）but also enhanced theζ-potential of the complex particles.The more negativeζ-potential was more conducive to the formation of electrostatic repulsion between emulsion droplets,which precipitated the dispersion of droplets more uniform and stable.The appearance,micromorphology,rheology properties,texture characteristics,and storage stability of the Pickering emulsions indicated that the oil phase mass fraction（φ）andβ-CD/citrus pectin ratios（Rβ/C）had the greatest impact on the printing properties of Pickering emulsions.The Pickering emulsions had good stability,viscoelasticity,shear thinning ability,and self-supporting force when theφ=65%and R_β/C=2:2,achieving the conditions for 3D printing materials.Moreover,the printed of two-dimensional mesh models and three-dimensional hollow square cylinder models expressed that the Pickering emulsions prepared byβ-CD/LP complexes was more suitable for printing delicate structure models.（3）4D printing discoloration of Pickering emulsions induced by p H.A new 4D printing material was prepared based on Pickering emulsions,containing Na HCO₃ and p H-sensitive natural pigment（curcumin/shikonin）.The temperature-induced thermal decomposition of Na HCO₃ changed the alkaline environment of the Pickering emulsions,which stimulated the p H-sensitive pigment to realize the 4D printing of the Pickering emulsions.The results showed that the appearance and structure of the Pickering emulsions containing p H-sensitive natural pigments had no abnormalities.The pigment concentration（C_P）,heating time（t）,heating temperature（T）,and sodium bicarbonate concentration(C_{Na HCO3})had an impact on the color change of 4D printing,and the C_P,t,and T had the most significant impact.When the 0%≤C_P≤0.075%,30℃≤T≤90℃,and 0 min≤t≤25 min,the printed Pickering emulsion samples had the best color change and the most ornamental.Moreover,the new 4D printing materials at the short storage time（4℃,6 days）had no effect on the structure of the Pickering emulsion and the discoloration effect of the internal pigments.Furthermore,the color change of the dual color model in 4D printing was achieved through a dual nozzle 3D printer,and the color of the dual color model showed a gradual color change with time gone,providing new ideas for the research of multi-color food 4D printing.In this study,the Pickering emulsions prepared byβ-CD/citrus pectin complexes have been successfully applied in food 3D/4D printing,which provides new ideas for the development of personalized food and a new way for the high-value utilization of citrus peel residue.