The Solution Properties Of Soybean Protein Isolate And Its Grafted Copolymer With Acrylic Acid

In this study, the graft copolymerization of soybean protein isolate (SPI ) withacrylic acid (AA) using ammonium persulfate (APS) as an initiator was carried out inan aqueous solution. In this copolymerization, the 8M urea and β-mercaptoethanolwere used to be denaturants for SPI. The FT-IR and 13C-NMR spectra of SPI and SPIgrafted acrylic acid copolymer (SPI-g-PAA) indicated that the AA had been grafted onthe SPI. The effects of APS, AA, reaction temperature, reaction time and ME on graftcopolymerization were studied by determining the grafting parameter such as graftingpercentage and grafting efficiency. The experiment results indicated that when theweight of SPI was 1g the optimum condition of reaction were [APS] = 15 mmol/L,[ AA] = 1.98mol/L, reaction temperature = 60℃, reaction time = 4h,[ME]=0.08mol/L. The effect of pH value on the solution behavior of SPI and SPI-g-PAA wasinvestigated by dynamic laser light scattering (DLS). The results indicated that theradius of SPI and SPI-g-PAA aggregates was related to the pH values. The averagehydrodynamic radius of SPI aggregate had the maximum value at its isoelectric point(pH = 4~5). The average hydrodynamic radius of SPI-g-PAA aggregates with the27.5% grafted percentage had the maximum at pH = 3~4. The average hydrodynamicradius of SPI-g-PAA aggregates with the 116.7% and 134.7% grafted percentage hadthe maximum at pH = 2~3. The solubility of the SPI-g-PAA in aqueous solutionincreased with increasing of the grafted percentages. Enzymatic hydrolysis process of soybean protein isolate (SPI) and the PAA-g-SPIcopolymer, the radius distribution of their hydrolysis products were investigated andcharacterized by dynamic laser lights scattering (DLS) and the ζ-potential methods.With the increasing of hydrolysis time, the average hydrodynamic radius ofhydrolyzed SPI aggregates deceased from 160nm to 110nm, the distribution ofhydrodynamic radius of SPI broadened, and the ζ-potential of SPI decreased from-24mv to about -37mv. The FTIR spectra of SPI before and after the hydrolysis byenzymatic (Alcalase3.0T) indicated that the hydrolysates of SPI have much morenon-associated O-H and N-H groups than that of native SPI. The enzymatichydrolysis of SPI finished in 3h. With the increasing of the enzymatic hydrolysis time,the average radius of PAA-g-SPI aggregate decreased from 161nm to 80nm, and theζ-potential of PAA-g-SPI decreased from -30mv to about -40mv. The enzymatichydrolysis of PAA-g-SPI finished in 2h. The hydrolysis ability of enzymatic( Alcalase3.0T) was more stronger for the SPI-g-PAA than for SPI.