| ?-carotene(?-CE)is an important organic pigment belonging to the family of carotenoids,which is abundant in vegetables and fruits.?-carotene,as a precursor substance of vitamin A,which has a rich nutritional value.In addition,the unique chemical structure of ?-carotene can effectively scavenge free radicals,so it is often used as an antioxidant and has the effect of detoxification.However,the poor solubility of ?-carotene in water and its instability in the presence of heat,light and oxygen make it limited in food processing applications where isomerization or oxidation tends to occur during mechanical action,thermal stress and storage,resulting in the loss of nutrients.In recent years,more and more researchers have used the method of encapsulating bioactive ingredients in an emulsion delivery system to overcome the disadvantages of low bioavailability,instability,and degradation of these bioactive materials.Emulsion-based delivery systems are particularly suitable for the delivery,protection,and release of fatsoluble bioactive ingredients such as polyunsaturated fats,oil-soluble vitamins,?-carotene and flavonoids.In emulsion delivery systems,emulsifiers can protect and deliver lipophilic bioactive ingredients.Milk fat globule membrane protein(MFGMP)is a membrane protein extracted from milk fat,which is a mixed protein and contains a variety of beneficial individual proteins.MFGMP has special biological activities,such as anti-cancer,anti-bacterial,enhanced immunity and physical fitness.In addition,MFGMP has amphoteric properties because it possesses a hydrophilic group and a hydrophobic group,so MFGMP can be used as an emulsifier to deliver fat-soluble bioactive components.Adsorption of MFGMP on the surface of oil droplets can increase the electrostatic repulsion between oil droplets,thereby preventing the flocculation and aggregation of oil droplets.Compared to lower molecular weight proteins,high molecular weight MFGMP has a higher oil droplet surface protein coverage and can increase emulsion stability.In this experiment,MFGMP was used as an emulsifier to prepare ?-CE-enriched emulsions,and then explored the influencing factors of emulsion formation.The results showed that the particle size of the ?-CE-rich emulsion gradually decreased with the increase of MFGMP concentration.There is no stratification of the liquid,indicating that MFGMP has good emulsification.The final conditions for the formation of ?-CE-enriched emulsions with MFGMP as emulsifier were as follows: oil phase is soybean oil,the MFGMP concentration was 3%,homogenizing pressure at 100 MPa,the number of homogenization was 5 times,oil to water ratio is 10%,and the content of ?-CE is 0.02%.By analyzing the stability of ?-CE-enriched emulsions under different environmental conditions,it has found that p H has a greater influence on the stability of the emulsion.When the p H is between 6.0 and 10.0,the emulsion is stable;the emulsion is also stable at a certain ion concentration(0-500 m M Na Cl);the ?-CE-enriched emulsion has good thermal stability,and MFGMP can protect the ?-CE from degradation under high temperature conditions.In the process of 25 days storage at different temperatures,although the particle size of the emulsion slightly increased,there was no significant change,which indicates that the emulsion is more stable.The in vitro static simulated digestion experiment was performed to analyze the physicochemical properties of the emulsion at various stages of digestion(oral cavity,stomach and small intestine).The experimental results show that compared with the initial solution,the confocal laser-scanning microscope(CLSM)and the particle size distribution of the ?-CE emulsion after oral digestion are basically the same,indicating that the physical and chemical properties of the ?-CE emulsion are not significantly changed.From sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE),it can be concluded that a large amount of MFGMP was digested by pepsin after gastric digestion.From the CLSM and the particle size distribution,it can be seen that the oil droplets begin to aggregate and flocculate in the gastric digestion process and the emulsion stability decreases.In the small intestine digestion stage,oil droplets are digested by pancreatic lipase into monoglycerides and free fatty acids.It can be seen that a large number of oil droplets are digested by pancreatic lipase in the small intestine digestion stage by the CLSM and particle size distribution analyzing.However,there are still a small number of oil droplets with large particle diameters,which are mainly caused by the interaction of digestive products digested with pancreatic lipase and substances such as bile salts.?-CE is gradually released from the oil droplets as enzymatic hydrolysis of the oil droplets of the emulsion occurs,which is a targeted release process.The degree of release is about 80%.In the first 10 minutes,the release of free fatty acids and ?-CE was faster,after which the degree of release did not change significantly. |
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