Studies On Graft Modification Of Soybean Protein Isolate, Layer-by-Layer Assembly And Application

The synthesis and application of soy protein isolate grafted copolymers have been investigated. SPI-g-PAMPS was synthesized in 8 mol/L urea aqueous solution initiated by ammonium persulphate under the protection of nitrogen (N2). Further, the solution properties of SPI and SPI-g-PAMPS, the application of the soy protein isolate in the field of SPI edible films, and Layer-by-Layer growth of nanoparticle- polylectrolyte multilayers on SPI were studied.SPI-g-PAMPS copolymer was characterized by Infrared Spectrometer and Nuclear Magnetic Resonance. The results indicated the AMPS had been grafted on the SPI. The influence of reaction conditions, such as initiator concentration, monomer concentration, denaturant concentration and time on percentage graft and percentage efficiency, were investigated. The results were that the percentage graft and percentage efficiency reached the maximum after SPI reacted for 4 hours.The percentage graft and percentage efficiency increased at first and then decreased with the increase of the initiator concentration, the monomer concentration and the denaturant concentration.The solubility, heat stability and hydrophobicity of SPI and SPI-g-PAMPS have been characterized by UV and Fluorescence. It was shown that the solubility and heat stability of SPI-g-PAMPS were better than SPI. Besides, the hydrophobicity of SPI-g-PAMPS decreased with its grafting percentage (GP%) increased.The effect of pH value on the solution behavior of SPI and SPI-g-PAMPS was investigated by Dynamic Laser Light Scattering (DLS). The results indicated that the radius of SPI aggregate was related to the pH values. The average hydrodynamic radius of SPI aggregate had the maximum value at its isoelectric point (pH≈4). The average hydrodynamic radius of SPI-g-PAMPS aggregate with the 36.5% grafted percentage had the maximum at pH≈3. The average hydrodynamic radius of SPI-g-PAMPS aggregate does not change a lot at the pH range of 2-13. The Zeta potential of SPI and SPI-g-PAMPS was studied by Zeta sizer. The results indicated that graft copolymerization could increase the charge of the surface of the SPI, which helped to enhance the stability of the SPI solution. Besides, the solution concentration and pH could change the Zeta potential of the SPI and SPI-g-PAMPS solution.SPI nanoparticles can be coated with oppositely charged polyelectrolytes using Layer-by-Layer (LbL) deposition as the sole method. Zeta potential and UV-visible spectroscopy confirmed that polyelectrolytes Poly(allylamine hydrochloride) (PAH) and Poly (sodium-4- styrenesulfonate) (PSS )were deposited onto the surface of SPI layer by layer. Thus LBL opens a new and general route for the functionalization of nanoparticles.The edible films were prepared from the aqueous solution of soy protein isolate mixed with Polyvinyl alcohol (PVA), glycerol and glutin. The effects of the mixture concentration on the tensile strength (TS), the elongations(E) and the transparency of SPI film were studied. The results indicated that PVA and glutin could enhance the tensile strength of the film greatly, glutin could enhance the tensile strength better than PVA does. The tensile strength could be 20.886MPa. PVA and glycerol could enhance the tenacity of the film greatly, and the combination of glycerol and PVA could enhance the elongation better than PVA or glycerol alone does.