| As nanoparticles can be used to encapsulate bioactive substances and stabilize interface, the preparation of nanoparticles with edible biopolymers have been receiving increased attention from researchers working in the food industry and become a hot spot in the field of food research. This work aimed at preparing a kind of multifunctional soy protein-based nanopatricles from soy protein isolate(SPI) hydrogel through a novel method with high pressure processing treatment. The mean size, zeta-potential and stability of the resulted nanoparticles, as well as the adsorption properties on the oil-water interface were studied at different p H values, heating temperatures, ironic strengths. Then Pickering emulsion(O/W) was prepared by homogenizing at 6000 r/min for 2 minutes, the storage stabilization of the resulted emulsion was investigated by observing the change of d4,3 of emulsion droplets. Also, experiments were carried out to testify the potential ability of SPI-based nanoparticle to encapsulate bioactive EGCG, which exhibits poor stability in neutral or alkaline solution. Besides, oleogels were obtained from emulsion stabilized by native SPI and nanoparticles through freeze-drying technology. The texture properties of oleogels and breads prepared from oleogel samples were analyzed. The main results can be described as follow:(1) With high pressure homogeneous technology, a kind of nanoparticle solution with clear appearance was prepared at p H values away from the isoelectric point of soy protein. The resulted nanoparticles could endure ironic strength to a certain degree and had good stability when they were subjected to heating treatment. The mean size of the nanoparticles were about 141~158 nm. Due to the covalent cross-linking induced by microbial transglutaminase, the nanoparticles exhibited rigid conformation. The surface hydrophobicity, surface pressure, surface dilatational modulus(E) were lower than native SPI. In addition, the contact angle(CA) at p H 5.0 which was detected by gel trapping technology, was close to 90 degree.(2) The O/W Pickering emulsions stabilized by native SPI and nanoparticles showed good storage stability at room temperature, d4,3 of droplets and creaming index after two months were almost the same as those of the fresh emulsions. Compared with emulsions stabilized by native SPI, nanoparticle-based emulsion had higher surface protein absorption and a thicker interfacial membrane was formed around the oil droplets. When it was subjected to centrifugation treatment, a higher speed was required to destroy the microstructure of the nanoparticle stabilized emulsions at the same p H values. After three freeze-thawing cycles, only emulsion with 2% nanoparticle concentration showed a great efficiency of trapping oil. The addition of glucono δ-lactone(GDL) made the nanoparticles form a three dimensional network around the oil droplets, leading to a self-support emulsion gel, while the emulsion stabilized by native SPI remains the same as before.(3) EGCG((-)-Epigallocatechin-3-gallate), a bioactive material, which is very unstable in neutral and alkaline solutions, degrades irreversibly to a yellowish-brown solution of the deterioration products, mainly through oxidation. The encapsulation efficiency of nanoparticle to EGCG is as high as 80%, the ability of scavenging DPPH free radical reach up to 79% when the EGCG concentration is 1.5wt%. The emulsion stabilized by the EGCG-loaded particles showed effective ability against lipid oxidation.(4) Oleogel samples were obtained from native SPI and particle stabilized emulsion by freeze drying. The particle oleogels showed better storage stability without obvious oil release after 10 months. Margarine, native SPI and particle oleogels were used to make breads, the springiness, cohesiveness and resilience decreased after three days, while the hardness increased. The nanoparticle oleogel could be used as shortening alternative and bread sample showed comparable texture properties to margarine bread. |
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