The Preparation Of Bilayer Emulsions Based On OSA Modified Starch And Chitosan Conjugates And Its Application In The Formation Of β-carotene Microcapsule

The microencapsulation of oil-soluble components can improve its stability and solubility in aqueous solutions.However,the emulsions formed by traditional methods for microcapsules preparation are susceptible to environment pressure,which will lead to the formation of microcapsules with lower shell strength and sealing performance.The microcapsules prepared based on the multi-layer emulsion can improve its stability,microcapsule efficiency and re-dissolving stability.In this study,bilayer emulsions based on octenyl succinic anhydride（OSA）modified starch and chitosan conjugates were made by high pressure homogeneous and electrostatic layer-by-layer self-assembly methods.The stability and performance of the emulsions under ambient pressure was analyzed.The microcapsules of P-carotene bilayer emulsions were prepared and optimized.The effects of different drying methods for microcapsule preparation were compared.The modeling of kinetic degradation of β-carotene in microcapsules was also investigated.The main contents and conclusions of this study are as follows:Firstly,the bilayer emulsion based on OS A modified starch and chitosan conjugates were prepared and opitimized by high-pressure homogenization and electrostatic layer-by-layer self-assembly method with mechanism of electrostatic adsorption.The stability of the emulsion was determined to optimize the preparation conditions of the bilayer emulsion.The optimized conditions for single layer emulsion was obtained by mixing 9%OS A modified starch with 15%MCT oil,and homogenized at 60Mpa for 6 times.Then the single layer emulsion was mixed with 0.75%chitosan solution at a mass ratio of six to four,and homogenized at 30 Mpa for 4 times to obtain the bilayer emulsion.The final composition of the bilayer emulsion was 9%MCT oil phase,4.59%OSA modified starch,and 0.3%chitosan.The particle size,PDI and Zeta potential of the bilayer emulsion were 182 nm,0.179 and 24.9 mV.The stability of the bilayer emulsion in the condition of heat treatment,pH,and ionic strength was investigated by the changes of particle size,Zeta potential and stability.Compared with single layer emulsion,the particle size and Zeta potential of the bilayer emulsion were less affected by pH,and stable under acidic condition.Although the ionic strength would affect the stability of the emulsion through the electrostatic shielding effect,the results showed that the particle size of the bilayer emulsion was less affected by the ionic strength.The bilayer emulsion obtained had more resistance to the salts than single layer emulsion.The addition ofβ-carotene and co-drying agents had no significant effect on the stability of the bilayer emulsion.The microcapsules of β-carotene were prepared by spray-drying with OSA modified starch and maltodextrin as wall material added to the optimized bilayer emulsion.The parameters of the spray-drying were optimized by single factors and response surface experiments.The microcapsule efficiency,water content and yield rate were used as the evaluation stands.The optimized results were obtained as follows:OSA modified starch and maltodextrin mixed at a mass ratio of 1:1.87,the wall material concentration of 19.52%,inlet temperature of 184.5℃,injection volume of 1100 mL/h.The comprehensive score of optimized microcapsule was 97.465,which was close to the model predicted value of 97.977.The results showed that the regression equation could predict the relationship between the factors and the properties of microcapsules well.The effects of spray drying and freeze drying on the properties of microcapsules based on bilayer emulsion were compared.The spray-dried microcapsule had more uniform particle size,higher solubility,lower water content,which was more favorable for storage.The difference of particle size and size distribution between primary emulsion and reconstituted emulsion was not obvious,indicating that the effect of drying methods on emulsion stability was little.The results of scanning electron microscope（SEM）showed that the microcapsules obtained by spray drying were ball-shaped,and surface wrinkled.The surface of the freeze-dried powder was porous and irregular in shape.The infrared spectrum of the microcapsule showed typical C=O peak at 1741 cm^-1,which indicated that there was interaction between OSA-modified starch and β-carotene.The stability of β-carotene microcapsule with different temperature and light were investigated by using β-carotene as retention index.The results showed that microcapsule methods could improve the stability ofβ-carotene compared with the β-carotene crystals.The β-carotene retention ratio of microcapsules based on bilayer was larger than that of single-layer emulsion.On the other hand,the β-carotene retention ratio of spray-dried microcapsules was larger than that of freeze-dried microcapsules.The kinetics of degradation of β-carotene was fitted by first-order kinetic model and Weibull model.The degradation rate ofβ-carotene of spray-dried microcapsule based on bilayer emulsion was small,indicating its good stability in different simulated conditions.