Preparation And Stability Of Anthocyanins Double Pickering Emulsion

Anthocyanin is a natural water-soluble pigment with anti-oxidation,anti-cancer,vision protection and other functions.Due to its large amount of unstable phenolic hydroxyl groups and its sensitivity to external environment such as pH,temperature and light,encapsulating anthocyanins is the primary means to improve its stability and achieve its application.Firstly,the anthocyanin oil-in-water?W/O?emulsion was constructed,and then the anthocyanin double Pickering emulsion was prepared by hydrophobically modified quinoa starch.The effects of the stability of anthocyanin in vitro simulated gastrointestinal digestion and different pH and ionic strength were researched.The results had theoretical and practical significance for improving stability and expanding application of anthocyanin.The anthocyanin W/O emulsion was constructed by using polyglycerol polyricinoleate?PGPR?,as an emulsifier,and stored at 4,25 40?,respectively.The volume fraction of 10-40%aqueous phase was suitable to form uniform emulsion.The particle size of the emulsion is 1-2?m.As the storage time increased and the temperature increased,the particle size of the emulsion increased to 2-3?m.Samples with 20-40%of the aqueous phase volume fraction had higher encapsulation efficiency of anthocyanins and the encapsulation stability of them were higher at low temperature,more than 75%after 15 days.At high temperature,each sample had poor encapsulation stability of anthocyanins,only close to 10%after 15 days resulting for rapid degradation of anthocyanin.High temperature made the emulsion unstable and stratified,so the oil phase was oxidized and rancid.The anthocyanin might be lost as an antioxidant against the free radicals produced by the rancidity of the oil.Therefore,the W/O emulsion was only suitable for the encapsulation of anthocyanins at low temperature and short-term at room temperature.The effects of the degree of substitution,PGPR concentration,internal water phase?W₁?and oil phase?O?volume proportion,starch concentration and?W₁/O?and external water phase?W₂?volume proportion on the visual appearance,microstructure,particle size distribution and encapsulation efficiency of anthocyanin in double Pickering emulsion were explored.The optimum process conditions were PGPR concentration of oil phase of 2%?w/v?,modified quinoa starch with substitution degree of 0.0421,the concentration of total emulsion volume of6%?w/v?,the volume proportion of each phase of?W₁/O=3:7?:W₂=6:4 and 5:5.The emulsion prepared by the optimum process conditions was proved to be a double Pickering emulsion by laser confocal microscopy and they remained stable after 7 days.The encapsulation stability of anthocyanin decreased from about 97%to 60%.The contact angle of quinoa starch increased after hydrophobic modified,which was beneficial to the uniform adsorption of starch on the water-oil interface,thus forming double Pickering emulsion.However,the pH of each phase in contact with anthocyanin was close to neutral,resulting in faster degradation of anthocyanin.The results of simulated in vitro gastrointestinal digestion showed that the morphology of the emulsion was basically maintained after the simulated gastric fluid,and the encapsulation stability of anthocyanin was about 86%.After in simulated intestine fluid,the anthocyanin retention rate,the starch hydrolysis rate and the free fatty acid release rate were about 40%,30%and 45%,respectively.The highly substituted modified quinoa starch had resistant starch,which was used as an outer layer of Pickering emulsifier to resist partial digestion of the stomach and small intestine,and protect the anthocyanin from pH and temperature changes to some extent.The visual appearance,microstructure,encapsulation efficiency and encapsulation stability of anthocyanin in double Pickering emulsion prepared at different pH and ionic strength were investigated.It was found that when pH=1,the emulsion layered and the particle size was larger,the encapsulation efficiency of anthocyanin was lower?85-90%?,but the encapsulation stability was higher?over 85%?.When pH=3-7,the encapsulation efficiency of anthocyanin was up to more than 95%,while the encapsulation stability was lower.With the increase of ionic strength,the particle size distribution of the emulsions was not uniform,and the stratification of emulsions were more obvious,but the encapsulation stability of anthocyanin was higher.The decrease of pH and the increase of ionic strength reduced the surface charge amount of the modified quinoa starch,so the electrostatic mutual repulsion between the starch granules decreased and the starch aggregated,thereby causing instability of the emulsion.