| Sesame is a common oil crop.Sesame meal after oil extraction has high protein content and comprehensive amino acid composition,which is an excellent plant resource for protein extraction.Sesame protein isolate and its components were obtained from defatted sesame meal by alkaline solution and acid precipitation method and Osborne method,respectively.The physicochemical properties and processing characteristics of sesame protein isolate and its components,including albumin,globulin,gliadin and gluten,were compared and studied.Then,the O/W emulsion stabilized by sesame albumin was prepared,and the effects of oil phase volume fraction,albumin concentration and ionic strength on the particle size,rheological properties and microstructure of the O/W emulsion were investigated.The effect of albumin concentration on the emulsion delivery system of?-carotene was also investigated.(1)Four sesame protein components were separated by Osborne method,and their physicochemical and functional properties were characterized.The solubility of each sesame protein component showed a U-shaped curve with the change of pH.Albumin showed better solubility than other protein components.The solubility of globulin,gliadin,gluten and sesame protein isolate is worse.SDS-PAGE profile showed that the main molecular weight distribution of sesame protein ranged from 10 k Da to 100k Da.the albumin showed the water holding capacity of 3.7 g/g,foaming capacity of273.2%and emulsifying stability index of 19.1 min;the globulin had the strongest fat holding capacity of 2.3 g/g and foaming stability of 82.2%;the gliadin had the highest emulsifying activity index of 23.7 m2/g.The contact Angles?w of albumin particles at pH 3.0,5.0,7.0 and 9.0 are 70.5°?73.7°?34.2°?56.4°,respectively,the results show that albumin exhibits good wettability under acidic conditions and is conducive to the formation of stable emulsion.The aggregation degree and surface charge of albumin particles were characterized by adjusting the pH value and ionic strength.The particle size of albumin particles formed at pH 3 was the smallest,the particle size distribution index value was the lowest,and the dispersion was uniform.Albumin was prone to aggregation near the isoelectric point.When the ionic strength is less than 100m M,the dispersion of particles is relatively uniform and good,and it has the potential to form emulsion particles.(2)Construction and characterization of O/W emulsion system stabilized by sesame albumin.pH,volume fraction of oil phase,protein concentration and ionic strength are the main factors affecting the properties of albumin stabilized emulsion,which are characterized by droplet size and distribution,emulsion type,creaming index,microstructure and rheological properties.The results show that the emulsion formed by albumin at pH 3 has the best storage stability and is O/W type emulsion.In the experiment of storage stability,the average volume diameter D(4,3)and CI value of the emulsion were inversely proportional to the protein concentration and proportional to the volume fraction of the oil phase and the ionic strength.The microstructure of the emulsion showed that the size of the albumin-stabilized O/W emulsion drops decreased and the distribution was uniform with the increase of the protein concentration,but the effect of the oil phase volume fraction and the ionic strength on the size of the emulsion drops showed the opposite result.The confocal laser scanning microscope profile showed that albumin at pH 3 showed good surface activity and able to adsorption on the oil-water interface,which further illustrates the formation of O/W emulsion stability mechanism.O/W emulsion stabilized by albumin show the behavior of non-newtonian pseudoplastic fluid,and has given priority to elastic properties of the gel.(3)The effect of albumin concentration on the emulsion delivery system loaded with?-carotene.The results of protein concentration on the storage stability of loaded?-carotene emulsion showed that the protein concentration was positively proportional to the retention rate of?-carotene in the emulsion,which indicated that the albumin-stabilized O/W emulsion was an effective method to stabilize?-carotene.The results of protein concentration on the release rate of free fatty acids and bioaccessibility of loaded?-carotene emulsion during in vitro digestion process were shown,the release rate of free fatty acids and bioavailability of?-carotene were significantly affected by increasing the protein concentration in the emulsion.Albumin-stabilized O/W emulsions have a delivery system for the intestinal targeting and sustained-release effects of?-carotene. |
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