Fabrication Of Protein-polyphenol-carbohydrate Conjugates And Their Stabilization Effect On Functional Components

The conjugate-based delivery system can protect the biological activity of food functional components;improve their solubility,physicochemical stability and bioavailability.Binary or ternary conjugates fabricated by proteins,polyphenols and carbohydrates can give new functional characteristics of food products,which are important to the development of new multi-functional food ingredients and food fortification.In this thesis,different proteins,polyphenols and carbohydrates were used to form functional conjugates.The reaction mechanisms were studied;the stabilization and delivery of the functional components by the conjugates were investigated.The contents and conclusions are listed as follows:(1)Fabrication and characterization of lactoferrin-polyphenol conjugatesAccroding to free radical grafting and alkali methods,lactoferrin(LF)and three different polyphenols(EGCG,chlorogenic acid(CA)and gallic acid(GA))were used to fabricate protein-polyphenol conjugates.The free radical grafting method was mainly based on the generation of hydroxyl radicals,and the mechanism of alkali method was mainly due to the oxidation and nucleophilic addition of polyphenols,the oxidation products of polyphenols could react with the nucleophilic groups of the protein.The covalent reaction reduced the a-helix content of the secondary structures of the protein,resulting in an increase in the content of unordered curl.The thermal stability and antioxidant activity of the covalent products were also enhanced.The conjugates prepared by the alkali method had higher polyphenol binding equivalents.(2)Functional properties and applications of LF-polyphenol conjugatesAt neutral conditions,the LF-polyphenol conjugates can inhibit protein aggregation.The results showed that LF had more secondary structure changes than LF-polyphenol conjugates during the thermal treatment,and the ζ-potential of lactoferrin covalently bound to polyphenols increased and the surface hydrophobicity decreased,the turbidity was lower than LF,which was mainly due to the greater steric hindrance and electrostatic repulsion of LF-polyphenol conjugates.β-Carotene bilayer emulsions were prepared using LF,LF-polyphenol conjugates and polysaccharides.Compared with the protein-stabilized emulsion,emulsions prepared with LF-polyphenol conjugates showed stronger stability against freezing and thawing,high ionic strength and heat treatment and improved chemical stability of β-carotene against light and heat.Addition of pectin and soybean polysaccharide could change the rheological property and stability of the emulsions.(3)Formation mechanism and physicochemical properties of lactoferrin-chlorogenic acid-carbohydrate ternary conjugatesBased on the Maillard reaction,the ternary covalent complex was synthesized by LF-CA binary conjugates and glucose/polydextrose.The grafting ratio was 11.72～40.50%and the ternary covalent complex had higher average-molecular weight.Glycosylation covalent modification changed the conformation of the protein.The amino acid groups of the binary conjugate could react with the reducing end of the carbohydrates to form the ternary conjugates with a high antioxidant activity.(4)Application of lactoferrin-chlorogenic acid-polydextrose ternary conjugate in stabilizing 3-carotene emulsionThe β-carotene emulsion was prepared using ternary conjugate as the emulsifier.In the emulsion system,the protein was used to provide surface activity,carbohydrates provided a strong spatial stabilization,and polyphenols offered antioxidant activity.The ternary conjugates improved the hydrophilicity of the protein surface and enhanced the spatial repulsion between the oil droplets,and it had better emulsifying properties than the individual protein or binary conjugate,and enhanced the physicochemical stability of β-carotene emulsions.In the simulated gastrointestinal tract,the ternary conjugate-stabilized emulsion had a higher inhibitory effect on the aggregation of droplets and therefore increased the bioavailability of β-carotene.(5)Covalent mechanism of zein-polyphenol conjugate and its application in multi-nutrients delivery systemThe covalently bound zein-polyphenol conjugates exhibited a stronger thermal stability and antioxidant activity than the non-covalent complexes.Based on the anti-solvent method,the zein-EGCG conjugate-rhamnolipid(R)stabilized nanoparticles were fabricated and used to co-encapsulate curcumin and resveratrol.The entrapment rates of curcumin and resveratrol were 71.2%and 85.4%,respectively.The resulting nanoparticles exhibited diameters of less than 200 nm and had narrower size distributions.Spectroscopic analyses showed that R was in the outer layer of the nanoparticles,and the entrapped active components were mainly bound to the binary conjugate by hydrophobic interaction.The bioavailability of curcumin and resveratrol was significantly improved by the addition of emulsion to the nanoparticles.