| As a natural functional ingredient with multiple physiological activities,?-carotene can maintain human health,prevent chronic or degenerative diseases,and promote infant growth and development.However,many conjugated double bonds in the molecular structure of ?-carotene make it very sensitive to environmental pressure such as high temperature,ultraviolet radiation and oxygen,and all kinds of free radicals and transition metal ions also facilitate the oxidative degradation of ?-carotene.As a fat soluble functional material,?-carotene is difficult to dissolve in the water environment of human digestive system,so that the absorption of human body is limited,and the strong acid environment in the stomach will also accelerate the degradation of beta carotene.Therefore,natural ?-carotene is not only difficult to be preserved for a long time,but also has low bioavailability.In order to enhance its chemical stability and bioavailability,this project tried to estabilish a ?-carotene delivery system.By analyzing and comparing all kinds of delivery systems with different functions based on the consideration of economic cost and target controlled release,the bilayer emulsion was selected as the experimental object finally.The composition and preparation conditions of the ?-carotene bilayer emulsion,the physical and chemical stability during the different processes,drying characteristics and digestion characteristics of bilayer emulsion were systematically studied in this project.The main results were as follows:(1)The bilayer emulsion was designed and prepared.The bilayer emulsion BSA/GA-e chose bovine serum albumin(BSA,15 mg/mL)as the inner emulsifier and Arabia gum(GA,15 mg/m L)as the outer emulsifier.The monolayer emulsion BSA-e was prepared after first high-pressure homogenization,and it was blended with GA solution by the mass ratio of 2.5:7.5.The bilayer emulsion BSA/GA-e was prepared after adjusting the mixed solution to 4.0 and second high-pressure homogenization.Compared to monolayer emulsions GA-e and BSA-e,the bilayer emulsion had a small droplet size(221.27±5.17 nm)and distribution(PDI = 0.23±0.02),strong zeta potential(-30.37±0.71 mV),good rheological behavior(with the highest viscosity that could reduce the possibility of flocculation)and physical stability(CI=0),high ?-carotene encapsulation ratio(94.35 ± 0.71%),low interfacial tension(40.81 ± 0.86 mN/m),highest viscosity(p<0.05),ability to shear thinning and good rheological properties.(2)The stability of BSA/GA-e under different environmental factors and processing conditions was studied.The results showed that ordinary metal ions(monovalent and bivalent),water bath constant temperature heating and freezing thawing were more likely to have adverse effects on the physical stability of BSA/GA-e(p<0.05).The ?-carotene in BSA/GA-e could maintain high chemical stability during the treatment of water bath heating,microwave heating,freezing and thawing,ultraviolet light and strong oxidant(p<0.05).In the storage process at different temperatures(4°C and 25°C),the degradation rate of ?-carotene in the internal oil phase of BSA/GA-e was the least,and the physical stability was the best(p<0.05).(3)The physicochemical properties of BSA/GA-e after freeze-drying and spray drying were compared.The results showed that products prepared by freeze drying had flake structure,better protective effect for ?-carotene,but more water content and the preparation process was tedious and time wasting;Microcapsules prepared by spray drying had granular structure,low water content,convenient and fast preparation process,but worse ?-carotene protective effect and more loss of sample.Freeze drying process caused less adverse effects on the particle size,PDI and potential of emulsions compared to spray drying(p<0.05)after redissolution.During the process of spray drying,maltodextrin did not affect the microstructure of BSA/GA-e microcapsules.With the increase of maltodextrin concentration,the water content of BSA/GA-e microcapsules did not increase significantly(p>0.05).The loss of ?-carotene in BSA/GA-e microcapsules was always lower than that of single layer emulsions,but its water content was relatively high.The drying process was more likely to have adverse effects on the droplet size,PDI and potential of bilayer emulsion(p<0.05).(4)The pH responsiveness and digestive characteristics of BSA/G-e were studied.By analyzing the physical and chemical properties of BSA/GA-e under different pH,it is confirmed that BSA/GA-e had pH responsiveness: when pH was 1.0~3.0,GA was attached to the film;when pH was 5.0~7.0,GA gradually desorbed from the film formed by BSA;when pH was 7.0~10.0,GA desorbed from the film totally.Therefore,BSA/GA-e could guarantee no release of oil in simulated gastric digestion stage(p H=2.5),but release at a certain rate in the simulated small intestine digestion stage(pH=7.0)furing in vitro digesting experiments,which ensured the absorpation of ?-carotene in small intestine at a slow rat.This process improved the ?-carotene bioaccessibility effectively(p<0.05).The ?-carotene bilayer emulsion BSA/GA-e designed in this project had small instine targeted controlled releasing effect and provided an important way to promote the practical application of ?-carotene in food,medicine and other fields,and it also enhanced the ?-carotene bioaccessibility in human body. |
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