Preparation,Characterization,and Antioxidant Activities Of Low Density Lipoprotein-Tremella Fuciformis Polysaccharide Complex

Polysaccharides and proteins are important biomacromolecules.Generally,the complex formed by polysaccharides shows better solubility,emulsification,stability,and antioxidation than their monomers.The complex is often used to improve the functional properties of monomers.Tremella fuciformis polysaccharide（TFP）has good hydrophilic and antioxidant activity.Low density lipoprotein（LDL）has good emulsification and gel properties.There are few studies on the formation of LDL-TFP complex.In this study,LDL,TFP,and LDL-TFP complex were prepared and characterized.In this study,asymmetrical flow field-flow fractionation（AF4）coupled online with ultraviolet-visible（UV）,multiangle light scattering（MALS）,and differential refractive index detectors（d RI）was employed to study the stability of LDL in egg yolk plasma modified by phospholipase A₂（PLA₂）.The AF4 results showed that PLA₂ modification enhanced the stability of LDL in terms of heat treatment and-18℃storage.Alkaline condition（i.e.,p H 10）promoted the aggregation of egg yolk plasma regardless of modification with PLA₂.However,PLA₂ modification promoted the aggregation of egg yolk plasma at the strong power of HIU treatment（i.e.,400 W）.In the second part,the physicochemical properties and structure of TFP obtained by different drying methods of Tremella fuciformis（i.e.,vacuum freeze drying,microwave drying,and hot air drying）were characterized by AF4,scanning electron microscopy（SEM）,fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）,and differential scanning calorimetry（DSC）.The results showed that the content of TFP extracted by microwave drying was the highest,the size of Tremella fuciformis dried by microwave drying was relatively small and uniform.No obvious difference in the functional group structure and crystal structure among three kinds of TFPs was observed.AF4-MALS-d RI results showed that TFP was a homogeneous polysaccharide.Under the same AF4 operating conditions,no significant difference in R_g and M_w of TFP extracted from Tremella fuciformis dried by microwave drying and vacuum freeze drying was observed,while TFP extracted from Tremella fuciformis dried by hot air drying contained large particles.The determination of chemical antioxidant capacity in vitro showed that 1,1-diphenyl-2-picrylhydrazyl（DPPH）free radical scavenging ability of TFP extracted from Tremella fuciformis dried by microwave drying was the best.Finally,the LDL-TFP complex was prepared and characterized by Zeta potential assay,AF4-UV-MALS-d RI and FTIR.The AF4-UV-MALS-d RI results showed that the R_g and M_w of the covalent complex formed by unmodified LDL and TFP at the ratio of 1:1（w/w）were larger than those of the PLA₂-modified LDL.The determination of chemical antioxidant capacity in vitro showed that the DPPH radical scavenging ability of TFP was significantly improved by LDL modification.Combined with in vitro cell antioxidant assay,the results showed that the structure of LDL-TFP complex affects the antioxidant capacity.The PLDL-TFP showed the best antioxidant capacity.In this study,the stability of PLA₂-modified LDL,the physicochemical properties and structural of TFP extracted from Tremella fuciformis obtained by different drying methods were evaluated.Preparation,characterization,and antioxidant ability of LDL-TFP complex were studied.Furthermore,the ability of AF4-UV-MALS-d RI to characterize LDL,TFP and LDL-TFP complex was investigated.The antioxidant activity of TFP was improved by LDL modification,and the modification effect of LDL modified by PLA₂ was the best,which provides a theoretical basis for the further application and development of antioxidant function of TFP.