Preparation And Characterization Of DNA-bioactive Compound Complexes And DNA-bioactive Compound-zein Composite Particles

Deoxyribonucleic acid(DNA)is a polyanionic and biocompatible biological macromolecule.DNA is able to form complexes with ligands because there are different binding modes and binding sites between DNA and ligands,making DNA an ideal carrier material.The interaction between DNA and ligands varied with structures of DNA and ligands,experimental conditions,and analytical methods,which are complex and still obscure.The key to developing DNA-based carrier systems is the elucidation of ligand binding properties.DNA has good structure stability and hydrophilicity.Meanwhile,based on the self-assembling propertities of both DNA and proteins,DNA-protein composite particles can be fabricated through co-assembly,which are expected to overcome the disadvantages(such as poor pH stability)of protein carriers.Moreover,combination with encapsulation technology in food field can realize the development of food functional carrier systems.In this study,calf thymus DNA was chosen as B-DNA model.The interaction between DNA and bioactive compounds was studied to explore the formation mechanism of molecular complexes between DNA and bioactive compounds.Furthermore,DNA and DNA-bioactive compound complexes can be used as shell parts to prepare DNA-zein composite nanoparticles to study the stability of core-shell structural complexes and the encapsulation and protection for bioactive compounds.These results might provide theoretical basis for the design of new functional food carriers.The main research contents are as follows:1.Study on the interaction of DNA-bioactive compounds complexes.Bioactive compounds including caffeic acid,riboflavin,quercetin,curcumin,resveratrol,naringenin,hesperetin,kaempferol,and apigenin were used as model ligands to interact with DNA.Their binding properties were analyzed by competitive displacement assay and the binding constants at different binding sites were calculated.The influence of interaction on bioactive compounds was analyzed by fluorescence,absorption,and ABTS assay.Circular dichroism and infrared spectroscopy were used to analyze the influence of bioactive compounds on the structure of DNA.Based on the interaction mechanism between DNA and bioactive compounds,the preparation of DNA-diligand complexes was discussed.The binding constants of bioactive compounds at the intercalative site of DNA ranked in order kaempferol(29)apigenin(29)quercetin(29)curcumin(29)riboflavin,while the binding constants at minor groove sites ranked quercetin(29)kaempferol(29)naringenin?apigenin(29)hesperetin(29)curcumin?resveratrol?riboflavin(29)caffeic acid.Bioactive compounds preferentially bound to guanine bases and tended to transfer into a more hydrophobic environment upon complexation with DNA.The DNA complexation did not affect the ABTS×~+scavenging capacity of quercetin,kaempferol,resveratrol and apigenin but increased the ones of naringenin,caffeic acid,curcumin,hesperetin and riboflavin.DNA maintained stable B-form with an enhancement of base stacking and a decrease of right-handed helicity in the presence of these bioactive compounds,except for hesperetin and caffeic acid.Moreover,DNA-diligand complexes could be formed when the sequence of ligand addition was riboflavin first and then naringenin.2.The preparation and characterization of DNA-bioactive compounds-zein composite particles.On the basis of the properties of ligand binding and self-assembly,DNA and zein were chosen as carrier materials to form core-shell structural nanoparticles for encapsulation and protection of bioactive compounds.The pH stability of DNA-zein composite nanoparticles was also explored to reveal the advantages.When the optimal mass ratio of zein to DNA was2.5:1,the size of core-shell structural DNA-zein composite particles prepared through electrostatic adsorption was 85.10 nm with a single peak distribution and the?-potential was-30.73 m V.What's more,the nanoparticles were dispersed uniformly with regular spherical shape and stable in a wide pH range.The encapsulation efficiency of kaempferol and?-tocopherol was 92.90%and 97.02%,respectively.Nanoparticles might mask the antioxidant activity of bioactive compounds partially.DNA coated on the surface of zein nanoparticles improved the stability of bioactive compounds during storage.Meanwhile,quercetin complexed to DNA on the surface of zein nanoparticles increased the antioxidant activity and storage stability of composite nanoparticles.