Nanogel Prepared By Plant Protein/Soy Polysaccharide Complex And Its Applications

In recent years, the plant protein have become a preferred alternative to animal-based protein because of increased consumer concerns over the safety of animal-derived products and their food choices based on moral, religious and cultural prohibitions. However, plant protein does not function effectively in acidic pH because they precipitate at pH values close to their isoelectric point which limits their applications in food and beverage industries.Protein/polysaccharide complex formed by the interactions between protein and polysaccharide can effectively combine properties of them to improve the deficiencies of protein. As a result, the complex and coacervates formed by protein and polysaccharide have a lot of excellent properties. By heating protein/polysaccharide complex and lockinga part of the polysaccharide chains in the gel core of protein, the protein/polysaccharide complex nanogels have been expected to bea delivery system of bioactive compounds in food and beverage.By now, however, the protein used to fabricate the nanogelsis limited to animal-derived protein and the long-term stability of the nanogelsis still a problem. For the application of the nanogels,the encapsulation, protection, and delivery of bioactive compounds have not been reported by now.In this thesis, we chose soy protein, pea protein and soy polysaccharide as materials to fabricate long-term stable protein/polysaccharide complex nanogels. We also chose folic acid as a bioactive compound to investigate the encapsulation, protection, and release effects of the folic acid in folic acid/protein/polysaccharide nanogels. The thesis contains the following three parts:In the first section, we used soy protein and soy polysaccharide to fabricate the nanogels. We induced high pressure homogenization to break down the origin aggregates in soy protein and a heat treatment to make the protein denaturation and gelation. By manipulationof the interactions between protein and polysaccharide viapH adjustment, high-pressure homogenization, and heat treatment, we obtained long-term stable nanogels with a size of155nm at the optimal preparation conditions.The nanogels were characterized by AFM, ζ-potential etc. The results indicate that the nanogels have a sphere shape and core/shell structure. The shell is composed of polysaccharide and the core is the protein and a part of the polysaccharide. The nanogels can contains a large amount of water and also have hydrophobic patch inside. The nanogels are stable in the pH range of2-8and in the presence of NaCl. In the second section, stable folic acid/soy protein/soy polysaccharide nanogels were produced by the binding of the protein with folic acid and the binding of the protein with the polysaccharide at pH4.0via pH adjustment, high-pressure homogenization, and a heat treatment. The nanogels can prohibit the precipitation of the folic acid at pH4.0. More importantly, the protein and polysaccharide can protect the folic acid from photo degradation in the presence of UV light and oxygen.When the environment pH changes to neutral or high, the deprotonated folic acid can be releasedfast from the nanogels. Since most food and beverage are acidic, the folic acid/soy protein/soy polysaccharide nanogels are an ideal protection and delivery system for folic acid. In addition, the loaded folic acid can be quickly released in the intestine and play its biological function.In the third section, in order to solve the defects of soy protein hypersusceptibility, we preliminary prepared folic acid/pea protein/soy polysaccharide nanogels and investigated the folic acid loading, protection, and release effects. The results show that the pea protein nanogelsare not as stable as soy protein nanogels because of weaker gelation capability. However, when folic acid is loaded in the nanogels, we can obtain long-term stable folic acid/pea protein/soy polysaccharide nanogels. Possibly, the hydrophobic aggregation of the folic acid enhances thegelation of the pea protein. Similarly, folic acid/pea protein/soy polysaccharide nanogels have the same protection effect as folic acid/soy protein/soy polysaccharide nanogels.