Interactions Of Zein/Gliadin With Curcumin And Their Impacts On Encapsulation Properties Of Resultant Nanoparticles

Many bioactive substances have disadvantages such as poor solubility,low chemical stability and low bioavailability,leading to limitations in their application and development.These disadvantages can be effectively overcome by using colloidal delivery systems.Among many colloidal systems,prolamins are widely used as the encapsulation materials for the delivery of bioactives such as curcumin due to their relatively hydrophobic structure and the ability to self-assemble into nanoparticles under suitable conditions.For the self-assembled curcumin encapsulated prolamins nanoparticles,the driving force is mainly non-covalent interactions(e.g.hydrogen bonding,van der Waals forces and electrostatic,hydrophobic or π-π interactions).Studying the interactions between proteins and bioactive molecules will help to rapidly screen the most suitable wall materials for delivery systems,the most optimized preparation conditions and application scenarios.In this thesis,the interactions between zein/gliadin with curcumin under different p H,ethanol concentration,and temperature conditions were investigated,and the differences in the binding of zein/gliadin to curcumin were compared by calculating their temperature-dependent thermodynamic parameters,analyzing their structural changes;and the physicochemical and curcumin-encapsulation properties of zein/gliadin nanoparticles prepared under different conditions were studied and correlated to the interaction studies.This thesis is divided into four chapters:Chapter 1: An overview of the influence of protein molecular properties on the interactions between bioactive substances and protein molecules,the preparation of protein-based delivery systems,and a brief description of current research strategies on the mechanisms of interactions between bioactive substances and protein molecules.Chapter 2: The interaction of zein/gliadin with curcumin at different temperatures at 60%,70% and 80% ethanol concentrations and p H 7.5 was investigated and the temperaturedependent thermodynamic parameters were calculated;the physicochemical properties of curcumin encapsulated zein/gliadin nanoparticles prepared at different ethanol concentrations were compared.It was demonstrated by fluorescence quenching experiments that the static quenching of curcumin and zein/gliadin was dominated by 1:1 spontaneous binding to form a complex,and the interaction between gliadin and curcumin was dominated by electrostatic interactions,while curcumin with zein was dominated by electrostatic forces at 60% and 70%ethanol and hydrogen bonding was the main driving force at ethanol concentration of 80%.The binding affinity between curcumin and gliadin gradually decreased with increasing ethanol concentration,but that of curcumin-zein gradually increased with increasing ethanol concentration.The circular dichroism results indicated that curcumin affected the secondary structure content of zein/gliadin,but overall,its effect was not as great as that of ethanol concentration change.When the nanoparticles were prepared using zein/gliadin for loading curcumin,the change of EE and LC was basically consistent with the determined binding affinity values between curcumin and zein/gliadin.However,when gum Arabic added,the physical properties of nanoparticles completely changed,which indicated that the interaction of gum Arabic with zein/gliadin also affected the binding of the zein/gliadin to curcumin and thus its delivery effect.Chapter 3: The interactions of zein and gliadin with curcumin at p H 4.0 was investigated.The fluorescence quenching results showed that the binding of zein and gliadin to curcumin at p H 4.0 was dominated by hydrophobic forces.The binding affinity of gliadin with curcumin increased gradually with the increase of ethanol concentration,and the binding affinity of gliadin with curcumin was stronger than that of zein under this condition.The structure of zein became more disordered after curcumin was bound to zein.However,for gliadin,the β-sheet content increased after binding with curcumin.Under this acidic condition,when the nanoparticles were prepared using zein/gliadin for loading curcumin,the change of EE and LC was consistent with the binding affinity tendency.This study further suggests that fluorescence quenching-based technology on determining interactions can be a suitable screening strategy to find appropriate wall materials and preparation conditions to assemble the delivery systems.However,the screening method was not applicable when the binary system became a ternary system containing gum Arabic.Chapter 4: Summary and perspective.