Construction And Application Of Egg Yolk Low-density Lipoprotein Nanoemulsion

Nano-materials are widely used in the food field,from doping metal nanoparticles in food packaging to protecting food nutrients with natural or synthetic nano-materials as carriers.At present,the research status of food-based nanomaterials is good and has a good application prospect.Eggs are one of the most common and essential food sources in people’s daily diet,and they are trusted by people for their rich nutritional value,low consumption cost,and very broad sources.Low-density lipoprotein（LDL）in egg yolk is a micro-nano material with a typical"core-shell"structure,which is similar to liposome and has potential application value as a nano-delivery material.Based on LDL,this paper modified LDL,loaded with vitamin D3（VD3）and Paprika oleoresin（PO）to form a stable water-soluble system,so as to improve the application range of nano-materials in food processing.The main research results are as follows:LDL was treated with pH-shifting to reshape the molecular structure of LDL,so as to better realize its embedding and loading of fat-soluble active ingredients.The results showed that pH-shifting treatment（pH12-LDL）reduced the average particle size from 100.80 nm to51.59 nm,and the turbidity of the solution decreased by 27.7%.The image of the electron microscope showed that pH-shifting reshaped LDL molecules,resulting in a significant reduction in particle size of about 50%.At the same time,pH-shifting changed its thermal stability.DTG spectrum showed that compared with LDL,the thermal stability of LDL remolded by pH-shifting was significantly improved,and the maximum weight loss temperature of LDL changed from 381.9℃to 457.0℃.In addition,thermogravimetric analysis and Fourier transform infrared spectrum show that pH-shifting may partially hydrolyze the esters in LDL into fatty acid salts.The results of FTIR showed that pH-shifting hydrolyzed lipids in LDL into fatty acids.The results of SDS-PAGE and fluorescence spectrum showed that the protein in LDL was partially hydrolyzed,and the fluorescent chromophores decreased significantly.The circular dichroism spectrum showed that the content ofα-helix in the secondary structure of modified LDL protein increased.Under the condition of ultrasound-assisted pH-shifting,a natural,safe,and stable aqueous solution of vitamin D3（VD3）was constructed with pH12-LDL as the carrier.Fluorescence spectrum analysis showed that VD3 and LDL were strongly bound by pH-shifting,accompanied by static fluorescence quenching,and the binding constant was 6.19×10⁴ M^-1.At the same time,pH-shifting induced the stable dissolution of VD3 in a water system,and the addition of pH12-LDL promoted its storage stability.Ultrasonic treatment enhanced the combination of LDL and VD3(the combination constant increased to 2.56×10⁷ M^-1),reduced the particle size,and increased the zeta potential of the complex between LDL and VD3,thus improving the solution stability and storage stability of VD3.Ultrasonic-assisted pH-shifting can transform LDL to construct a stable water system of VD3,which shows the potential of LDL as a carrier of fat-soluble components.In this study,the dissolution of PO in water was realized,and the dissolution state of PO in an aqueous solution was studied by pH-shifting treatment.Through pH-shifting（pH=12）,PO has good solubility in an aqueous solution,but it does not show good stability.LDL is added to protect PO from harsh conditions（heat and ultraviolet rays）under alkaline conditions.After storage for 28 days,the retention rate of the color value of PO aqueous solution with LDL was13.91%higher than that of the control group（PBS-PO）without LDL.The solubility（44.86%）and storage stability of PO were significantly improved by ultrasonic assistance.Under a transmission electron microscope,it was observed that the particles of LDL-PO solution were smaller and better distributed.Using SAXS,we found that the distribution of LDL-PO aqueous solution was changed by ultrasound,and the particle structure changed from complex to simple.At the same time,the SAXS results show that the increase of the thickness of the inhomogeneous region of electron cloud density（14.41 nm→15.18 nm）and the appearance of high molecular weight protein in the solution may represent the formation of covalent bonds between LDL and PO.This may prove that ultrasound-assisted pH change promotes the combination between LDL and PO,and increases the solubility and stability in water.To conclude,we found a method to promote the stable water solubility of fat-soluble compounds,produced pigment products that can be directly applied,and directly applied this product to food development,achieving the expected research purpose.