| Anthocyanin,a soluble pigment,widely exists in natural world,and displays excellent properties of antioxidant,anti-cancer,anti-diabetes,anti-cardiovascular disease and other physiological function.However,the structure vulnerability of anthocyanins molecules endow them instable to a variety of physical-chemical factors,including pH,light,solvent and temperature,which vastly limit the applications of anthocyanins.Therefore,it is essential to study the stability and resistance to oxidation of anthocyanins,to explore protecting approaches for keeping anthocyanins from degradation.Design and preparation of functional microcapsules for embedding the anthocyanins would largely improve their stability as well as protect their physiological function from damaged.In this work,structures and stability of anthocyanins extracted from purple sweet potato(Shanchuan)were studied using HPLC-MS and ultraviolet and visible spectrophotometer.And antioxidant mechanism in vitro of 7 anthocyanins was also studied based on density functional theory.To improve the stability of anthocyanins,three functionalized wall materials were synthesized and characterized by 1H-NMR and IR.Additionally,physical and chemical properties,antioxidant capacity and cytotoxicity of the wall materials as-synthesized were also researched by integrated thermal gravimetric analysis,viscosity analysis,DPPH clearance test,lipid peroxidation inhibition test,and HEK293 cell toxicity test.Subsequently,purple sweet potato anthocyanins microencapsulations were prepared.And kinetics of degradation and in vitro release characteristics of non-encapsulated anthocyanins,traditional wall materials encapsulated anthocyanins and newly synthesized wall materials encapsulated anthocyanins were also studied.Regulating effect of microcapsule on antioxidant enzyme of Nrf2 cellular pathways as well as antioxidant mechanism of microcapsule were also studied.The work can be summarized as follows:(1)Structures of 7 anthocyanins extracted from purple sweet potato(Shanchuan)were determinated using HPLC-MS.Those anthocyanins were composed of 3 kinds of peonidins and 4 kinds of cyanindins.Among them,Peonidin 3-caffeoyl-p-hydroxybenzoyl sophoroside-5-glucoside and Cyanidin 3-(6'',6'''-dicoumaryl sophoroside)-5-glucoside were two most abundant anthocyanins,accounting for 20.1% and 21.1% of total,respectively.Those anthocyanins had a lot of acylation groups and glycosylation groups.(2)The content and stability of anthocyanins in purple sweet potato(Shanchuan)were studied based on UV-vis spectra.The content of anthocyanins from purple sweet potato is 261.9 mg/100 g,which was much higher than that of strawberry(35mg/100g)and purple cabbage(25mg/100g)determinated by pH differential method.And the stability of anthocyanins were easily influenced by changes of light,humidity and solvents.The content of anthocyanins would decrease as it was illuminated by natural light.An increasing water or ethanol contents would accelerate the degradation of anthocyanins.Within the concentration range of 0.0625-1mg/mL of anthocyanins,DPPH free radical scavenging rate and lipid peroxidation inhibition rate increased with the increasing concentration of anthocyanins.They reached 84% and 91%,respectively.(3)To clarify their relationships between structures and properties,B3LYP/6-31g(d)method of Density Functional Theory(DFT)was performed to interpret the mechanism of antioxidant and the effect of solvents on stability of 7 anthocyanins.Bond dissociation energy and electronic potential of anthocyanins in aqueous solution were ranged from 64.6 to 73.9 kal/mol,131.2 to 147.3kal/mol,respectively.Hydrogen atom transfer mechanism and electron transfer mechanism demonstrated that purple sweet potato anthocyanins displayed high antioxidant capacity.This method provided an academic reference to the development of antioxidant.(4)Three new wall materials(MD-g-FA,MD-g-CA and MD-g-VA)were synthesized using three cinnamic acid derivatives(Ferulic acid(FA),coffee acid(CA)and Vanillic acid(VA))and maltodextrin(MD)as raw materials via grafting modification technology and characterized by FT-IR and 1H-NMR.Under the optimal condition,the grafting degree of FA-g-MD,VA-g-MD and CA-g-MD were 0.81,0.76 and 0.24,respectively.An increasing viscosity and thermostability of new wall materials were verified by viscosity analysis and comprehensive thermal analysis.DPPH scavenging test and lipid peroxidation inhibition test demonstrated that antioxidant ability of new wall materials were much higher than that of traditional wall materials.Moreover,no obvious cytotoxicity was observed after incubation of the mixture of new wall materials with concentration ranging from 0 to 100?g/mL and HEK293 for 24 and 48 hours.These results suggested that the new wall materials would be potential candidate in the field of antioxidant microencapsulation.The approach presented here has potential application for the development of new wall materials.(5)Newly synthesized wall materials were used to microencapsulate anthocyanins.Some of microcapsules were sphere,others were flawed or plicate,which were verified by SEM images.Encapsulated efficiency of new wall materials were about 80%,which was larger than that of traditional wall materials of 69.2%.The degradation of purple sweet potato anthocyanins microcapsule was in accordance with the second order kinetics under different storage conditions,which demonstrated that FA-g-MD displayed excellent protection ability towards anthocyanins.In addition,the content of anthocyanin,the concentration of anthocyanin,the polymeric pigments concentration(PPC)and the browning index(BI)showed a good negative correlation.Simulative gastrointestinal digestion test in vitro showed that neutral environment have an important impact on both of non-encapsulated anthocyanin and the anthocyanins microencapsulated with maltodextrin.Residual rate of nonencapsulated anthocyanin and the anthocyanins microencapsulated with maltodextrin were 11% and 8% in gastrointestinal digestion test in vitro for 120 minutes,respectively,while that of anthocyanins microencapsulated with MD-g-FA was about 38%.(6)Antioxidant ability of anthocyanins microencapsulated with MD-g-FA,core materials and wall materials were studied through DPPH free radical scavenging and lipid peroxidation inhibition test.The test results showed that core materials and wall materials displayed synergism in antioxidant ability.The results of protein expression tests showed that the up-regulation of quinone oxidoreductase(NQO1)??-glutamylcysteine ligase(GCLC)and glutathione reductase(GSR)in the cellular pathways(Nrf2)were observed in microcapsules and their core materials and wall matrixes,respectively.Moreover,pretreament with these materials for 24 h enhanced the quantity of protein expression compared with that for 6h.Microcapsules showed higher inhibition effect on the reactive oxygen species(ROS)(EC50=264±11.8?g/mL).Among them,the expression of GCLC and NQO1 were enhanced by 217.5% and 229.2%,respectively. |
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