Preparation,Characterization And Application On Covalent Complexes Of Proteins And Flavonoids From Lycium Barbarum Leaves

In this study,five kinds of protein and flavonids from Lycium barbarum leaves(LBLF)were prepared by free radical grafting technology.The structure changes of these grafts were compared and their antioxidant properties were analyzed.Because of the strong binding force and antioxidant activity of whey protein(WP)and LBLF complex,the WP-LBLF was selected in the following experiments.To explore the emulsification of whey protein and its complex as emulsifier,and then WP-LBLF conjugates was used as antioxidant emulsifiers to stabilize emulsion-based delivery systems for?-carotene to improve its water-solubility,chemical and bioavailability stability.The main research contents and results are as follows:1.The covalent complexes Pro-LBLF,Soy-LBLF,CAS-LBLF,BAS-LBLF,WP-LBLF were prepared by free radical method.The structure and antioxidation of covalent compounds formed by different proteins and flavonids from Lycium barbarum leaves were compared.It was found that the highest polyphenol content in the complex was WP-LBLF(6.62 mg/g).After covalent reaction,the content of free amino group and thiol group of protein decreased.The binding ability of these two compounds was compared by ultraviolet,fluorescence,Fourier transform infrared spectroscopes.The effects of covalent binding of flavonoids and five proteins on protein structure were analyzed.The antioxidant properties of WP-LBLF were evaluated in vitro.The results of spectrum analysis showed that the five proteins had covalent effect and changed the protein conformation.The interaction between the two was confirmed by SEM,and the morphology of the samples changed before and after covalent recombination.Whey protein and flavonids from Lycium barbarum leaves have strong binding ability.The results showed that WP-LBLF had the strongest antioxidant activity,and the antioxidant activity was proportional to the grafting ratio of flavonids from Lycium barbarum leaves.2.Through the preparation of stable emulsion of WP and WP-LBLF under different pH values,it is found that under the condition of pH=8,the particle size of emulsion is smaller,and the particle size distribution is monodisperse.Therefore,in subsequent experiments,we chose the conditions of pH=8 to prepare emulsion.Moreover,WP-LBLF stabilized emulsion has stronger antioxidant activity than WP stabilized emulsion.The emulsion size of the covalent complex is smaller,but the creaming index is higher.Rheological behavior indicated that the addition of flavonids from Lycium barbarum leaves reduced the viscosity of the emulsion.3.Preparation of WP-LBLF compared with WP ?-Carotene emulsion can be improved.The storage stability of ?-carotene.The addition of flavonids from Lycium barbarum leaves.The retention rate of?-carotene was increased.It shows that the free radical graft pair ?-carotene has good protective effect,which is attributed to its strong antioxidant.In addition,in order to investigate the potential application of WP-LBLF in real food products,the effects of environmental factors(heat treatment and ionic strength)on the stability of emulsion were studied.The results show that the stability of WP-LBLF?-carotene emulsion has high thermal stability and salt resistance stability.Therefore,the grafting of whey protein and flavonids from Lycium barbarum leaves is more suitable as a new antioxidant emulsifier.