Structural Modification And Nanocomposites Of Mulberry Anthocyanin And Its Biological Characteristics

Anthocyanins are hydrophilic polyphenolic plant secondary metabolites.They possess a wide range of biological characteristics,such as antioxidant,antiaging,anti-inflammatory,antimicrobial and anti-cancer.Therefore,anthocyanins have a great potential in various fields,such as the pharmaceutical and food industries.However,the relatively low stability of anthocyanins limits its bioavailability and effective applications,raising up the importance of reducing the degradation of anthocyanins and controlling release.So far,structural modification and composite encapsulation are the two main means used for anthocyanin stabilization.The content of anthocyanins in mulberry is rich.The main component is cyanidin-3-O-glucoside,which is also an important source of natural pigment.In this project,mature mulberry fruit was selected.The anthocyanin was extracted with acidified ethanol solvent and purified by D101 macroporous resin.The structure of anthocyanins were modified by acylation and Fe₃O₄/anthocyanin magnetic biological nanocomposites and the new type of bio-based hydrogels were prepared.The biological characteristics and mechanism of action were discussed.The main results were as follows:?1?The anthocyanin of mulberry was acylated by bio-enzymatic method and compared with those of non acylated anthocyanin.Single factor experiments were used to screen the appropriate lipase and solvate,and the effect of different acyl donors on the conversions of anthocyanin acyl groups were investigated.The maximum conversion rate was 13.5%.The optimal conditions for the acylation reaction were determined by orthogonal experiments,in which candida antarctic lipase was the acylating catalytic enzyme,pyridine was the catalytic solvent,and methyl gallate was the acyl donor.When the reaction time was 12 h and the anthocyanin concentration was 2 mg/m L,the acylation effect was the best.The products were analyzed by Fourier transform infrared spectroscopy?FTIR?and high performance liquid chromatography-mass spectrometry?HPLC-MS?.It was identified that the acylated products may be monoacyl anthocyanin or polyacyl anthocyanin.?2?The effects of temperature,light and pH value on the stability of acylated anthocyanins were further researched.The acylation could improve the thermal stability,light stability and acid and alkali resistance of anthocyanins.At the same temperature,the retention rate of acylated anthocyanins increased by 5%.After 6 days of light exposure,the retention rate of acylated anthocyanins was still as high as 96.1%.The acylation could significantly increase the antioxidant activity of anthocyanin in vitro.DPPH radical scavenging activity was enhanced.The total reducing ability was 30%higher than that of the non-acylated anthocyanins.The metal ion chelating ability was up to 90%.The inhibition rate of acylated anthocyanins was 81%,while that of non-acylated anthocyanins was only 50%.Therefore,acylated anthocyanins can effectively inhibit cell proliferation.?3?The pH sensitive Fe₃O₄/anthocyanin magnetic biological nanocomposites were further prepared and the release effect of anthocyanin was studied.The magnetic Fe₃O₄nanoparticles were prepared through the hydrothermal synthesis method.Then cyanidin-3-O-glucoside standard was used as a natural pigment to investigate the effect of different mass ratios,reaction times,pH values and reaction temperatures on Fe₃O₄/anthocyanin magnetic biocomposite.When the mass ratio of anthocyanin to Fe₃O₄was 1:50,the reaction temperature was 60?,and the reaction was performed for 20 h in a solution of pH8,Fe₃O₄had the best adsorption effect on anthocyanins,and the reaction solution was clear and transparent.Through physical means,the release experiments of magnetic nanoparticles adsorbed with anthocyanins were performed.The effects of dissociation solvents,pH value,reaction temperature and time on the release of anthocyanins were analyzed.The absorbance method was used to determine the release efficiency of anthocyanins.When Fe₃O₄was compounded with anthocyanin,the release rate of the complex powder in the acidic methanol solution was 60.9%at one time,and the total release efficiency at two times could reach 80%.?4?A series of performance characterizations were carried out to evaluate the combination of anthocyanin and Fe₃O₄.The structural characteristics of functional magnetic nanoparticles were studied.The surface of Fe₃O₄nanoparticles was rough and the structures of the nanoparticles were porous,while the surface of Fe₃O₄/anthocyanin magnetic biocomposites became smooth.Transmission electron microscopy showed that the transparency of Fe₃O₄/anthocyanin magnetic biocomposites were greatly weakened.The average size of the Fe₃O₄/anthocyanin magnetic biocomposite was about 222 nm.Compared with the Fe₃O₄nanoparticles,the particle size of composites increased and the charge decreased.The new characteristic peaks from 1000 cm^-1to 1300 cm^-1on the curve of Fe₃O₄/anthocyanin composite caused by C-O stretch of anthocyanin proved that anthocyanin has been synthesized with Fe₃O₄.The synthesis mechanism of Fe₃O₄/anthocyanin magnetic biocomposite formed by-OH of Fe₃O₄,-OH of anthocyanin and-OH of alkaline solution in weak alkaline environment.And under acidic conditions,the Fe₃O₄/anthocyanin magnetic biocomposite dissociated into Fe₃O₄nanoparticles and anthocyanins to achieve the release of anthocyanin.?5?Based on the above research,Fe₃O₄bio-based hydrogels,Fe₃O₄/anthocyanin?ANC?bio-based hydrogels and proanthocyanin?OPC?bio-based hydrogels were prepared on the basis of PVA hydrogels,and their characteristics were studied.The self-healing process of the fractured hydrogel samples was induced by two methods of water and near-infrared radiation until all the wounds were healed.The new type of bio-based hydrogels have the function of water promoting healing.The water active dynamic borate bond was introduced into PVA hydrogels.The borate bonds consisting of borate ions complexed to the hydroxyl groups of PVA crystallites provided dynamic covalent crosslinking borate bonds via absorbing water,which allowed a chemical self-healing process to take place.Under near-infrared laser irradiation,self-healing can be induced.The maximum temperature of PVA/Fe₃O₄/ANC/EG hydrogel rised to 64?,with excellent photothermal performance.Compared with pure PVA hydrogels,the new bio-based hydrogels have better mechanical properties in terms of high tensile force and ultimate fracture displacement.The conductivity of PVA hydrogel was poor,with the voltage of22.4 mV,while the conductivity of the hydrogel added with graphite powder was greatly increased.The conductivity of PVA/Fe₃O₄/EG,PVA/Fe₃O₄/ANC/EG and PVA/OPC/EG hydrogel increased to 56.0 mV,52.0 mV and 63.6 mV respectively.The-OH group of proanthocyanidin?OPC?can form hydrogen bond with the nitrogen atom of the organic dye tertiary amine group and the oxygen atom of the sulfonic acid group,showing a good adsorption performance for the organic dye dissolved in water.The salt crystal?Na Cl?was loaded on the surface of the hydrogel,which was basically dissolved within 30 min and showed good anti-salt scale effect.Under the irradiation of infrared light,the hydrogels showed a strong thermal localization effect,which greatly reduced the heat diffusion to water,effectively controled the heat near the evaporation surface and reduced the unnecessary heat loss.The structure and properties of hydrogels were characterized and analyzed.The self-healing of new bio-based hydrogels followed physics?melting/recrystallization of hydrogels?and chemistry?reversible covalent cross-linking of borate bonds?self-healing induction mechanism and polyhydroxyl adsorption mechanism.Through the above analysis,the different acyl sites,acyl types and acyl numbers of anthocyanins in mulberry were determined to improve the stability of anthocyanins.Fe₃O₄/anthocyanin magnetic biological nanocomposites were prepared by physical intermolecular adsorption to realize the effective release of anthocyanin,so as to develop a new idea of controlled release and targeting of anthocyanin.Bio-based hydrogels had biological activity and photothermal effect.It can be applied to flexible wear,seawater purification,wound healing dressings and other fields,so as to provide theoretical basis and technical support for the application and development of natural anthocyanins.