Research On Preparation Of Protein-polysaccharide Complex Emulsion By Ultrasound Treatment

The emulsion is an essential part of the food industry.The emulsion can give the product a smooth taste and achieve the entrapment and transmission of food nutritive active components.The stable emulsion of the protein-polysaccharide complex has attracted more and more attention because of its good biocompatibility,degradability and stability.However,the traditional preparation methods of protein-polysaccharide complex and emulsion have some shortcomings,such as expensive equipment,high maintenance cost,minor sample treatment and so on,so they are not suitable for the industrial production of food emulsion.This study prepared casein-pectin complex emulsion loaded with bioactive components by sequential gradient ultrasound treatment.The preparation method of the casein-pectin complex regulated by ultrasound was constructed.The multi-scale structural and functional characteristics of the casein-pectin electrostatic complex were analyzed by modern instrumental analysis and spectral characterization techniques.The structural characteristics,functional properties,stability and loading characteristics of bioactive substances of the emulsion prepared by ultrasound were deeply studied,and the sequential gradient ultrasound stabilization mechanism of the protein-polysaccharide emulsion was revealed.The main conclusions of this study are as follows:（1）Casein-pectin complex was prepared by multi-mode divergent ultrasound.The optimal ultrasound treatment conditions for the preparation of protein-polysaccharide complex were determined through the single factor experiment:single frequency 60 k Hz,50 W/L,25min,dual-frequency combination 20/40 k Hz,30 W/L,25 min.After single-frequency ultrasound treatment,the particle size and emulsifying activity index of the complex were449.99 nm and 12.98 m²·g^-1.After dual-frequency ultrasound treatment,the particle size and emulsifying activity index of the complex were 469.12 nm and 12.49 m²·g^-1.The particle size decreased by 22.95%and 19.67%compared with the control group.The emulsifying activity index increased by 33.12%and 28.10%.Structural analysis showed that the proteinα-helix content in the complex decreased to 36.01%and 27.25%after ultrasound treatment.The protein structure unfolded,hydrophobic and charged groups tended to be exposed.Theβ-folding content increased to 18.35%and 20.85%,respectively.The binding strength of protein and pectin increased,and more hydrogen bonds were formed.At the same time,the denaturation temperature of protein in the complex treated by ultrasound increased to 67.35℃and 60.65℃,and the thermal stability was improved.The microstructure observation results of the scanning electron microscope（SEM）and atomic force microscope（AFM）showed that the size of the complexes decreased,and the self-aggregation decreased after ultrasound treatment.（2）The stable casein-pectin complex emulsion was prepared by concentrated ultrasound treatment.A single factor test determined the optimum conditions of ultrasound emulsion preparation,a dual-frequency combination of 20/28 k Hz,a power density of 1200 W/L,and a treatment time of 6 min.Under these conditions,the particle size of the emulsion was 3.09μm;the interfacial protein content was 76.61%,the interfacial polysaccharide content was 71.03%,and showed good stability,which the centrifugal stability of the emulsion was improved from25.62%to 91.78%.Raman spectra showed that the interaction between protein-polysaccharide complex and lipid was enhanced after ultrasound treatment.The rapid analysis of emulsion stability showed that the stability of emulsion prepared by concentrated energy ultrasound was significantly improved,and its instability index decreased from 19.26 to 0.99.The results of freeze-thaw stability showed that the crystallization temperature of emulsion decreased from-14.67℃to-15.48℃after concentrated ultrasonic treatment,and the temperature sensitivity of emulsion decreased.The microstructure observation results of optical microscope and laser confocal microscope showed that the particle size of the emulsion decreased,and the adsorption capacity of the protein-polysaccharide complex at the oil-water interface increased after ultrasonic treatment.The results of simulated digestion and lipid oxidation in vitro showed that after ultrasonic treatment,the release rate of free fatty acids increased from23.35%to 30.76%,the content of primary oxidation products decreased from 0.339 mmol/L to0.317 mmol/L,and the range of secondary oxidation products decreased from 4.642 mmol/kg to 3.613 mmol/kg.The emulsion has good lipid oxidation stability.（3）Delivery characteristics of casein-pectin complex emulsion prepared by sequential gradient ultrasound on bioactive substances.The results showed that the loading capacity of ultrasound emulsion to curcumin,β-carotene and quercetin increased significantly.The DPPH scavenging rate increased from 96.45%,97.09%and 87.73%to 97.63%,98.55%and 97.55%,respectively,and the hydroxyl radical scavenging rate increased from 85.36%,97.19%and86.70%to 88.30%,98.17%and 91.88%,respectively.The total reducing force increased from0.79,0.41 and 0.76 to 1.15,1.39 and 1.66.Compared with the control group after heat treatment and UV irradiation,the degradation rate of ultrasound-treated samples decreased by80.01%,81.42%,and 53.56%.After treatment at 50℃,75℃and 90℃for five hours,the degradation rate of curcumin in the emulsion prepared by sequential step ultrasound decreased by 85.31%,76.92%and 75.52%,and the degradation rate ofβ-carotene decreased by 80.50%,80.04%and 77.23%.The degradation rate of quercetin decreased by 53.44%,40.57%and30.58%.The results of the simulated digestion test in vitro showed that the absorption rates of curcumin,β-carotene and quercetin increased from 35.50%,16.14%and 12.20%to 86.50%,25.30%and 48.11%.