Study On Enhancing The Surface Activity Of Soybean 11S Protein By Chemical Modification

The soybean 11S protein is one of the most important components of soybean protein isolate.However,the globular structure blocked the display of its surface activity.So in this experiment,the self-made soybean protein 11S was applied as modified raw material to study the effects of hydrogen peroxide and sodium chloride on its structures and properties.Three important conclusions were drawn.1.At first,the purified soybean 11S protein was treated by hydrogen peroxide with different concentrations.After that,the samples were lyophilized but later those freeze-dried samples were dissoved.The effects of modification conditions on the structure and properties of soybean 11S protein were determined.The results showed that the disulfide breaking rate increased gradually with the thickening of hydrogen peroxide.At the concentration of 100mmol/L,the disulfide bond breaking rate was92.79%,the emulsification and foaming was most sharply marked.Under these conditions,the?_CMC value was 55 m N/m and CMC was 0.1 g/L,they got the characteristic of surfactant.The HLB value was 10,indicating the relative stronger lipophilicity.By means of the fluorescence spectrum,infrared spectrum and circular dichroism,it is evident that the structure of the soybean 11S protein after oxidation treatment of hydrogen peroxide turned to?+?from?.The molecular of expansion in its structure become more flexiber,At the same time,the internal hydrophobic residues exposed and the surface hydrophobic group on surface increases with the improvement of hydrophobicity.In terms of particles distribution through Atomic force scanning?AFM?the size of soluble protein particles of soybean protein 11S shrank but its uniformity improved after 100 mmol/L hydrogen peroxide treatment.Therefore,the oxidation makes higher performance of soybean protein 11S in the solution.2.In the second round we have taken sodium chloride solution of low concentration among different rank to purify the soybean protein 11S.In the same way,the structures and performance of lyophilized samples were determined.The emulsifying and foaming property of 11S rise at first but then decreased with the thickening of NaCl solution.When NaCl concentration run up to 50 mmol/L,the emulsifying and foaming properties of soybean protein 11S reached peak.Likely the?_CMC value was 63.3 m N/m and CMC was 0.14 g/L.They kept the characteristic of surfactant.The lipophilicity was slightly increased with the HLB value 10.Since Na⁺can change the charge distribution on the surface of soybean protein 11S but affect little on the subunit structure of protein molecules.It can be seen that Na⁺does not make big variant from protein structure using fluorescence spectroscopy,infrared spectroscopy and circular dichroism.Although that if the process was observed under the AFM and analyzed in a PSD perspective,something differs.By changing the charge distribution on the surface of the protein molecule,the grain of protein molecules in the solution presented better uniformity.So thus the surface activity of soybean 11S protein was eventually improved.3.At last time,we set out to oxidixe soybean protein 11S by hydrogen peroxide based on 50 mmol/L of NaCl solution and take advantage of different concentration gradients.So that the emulsification and foaming of commercial sodium caseinate can be compared.To all appearances,Oxidation brook off the disulfide bonds among protein molecules leading to the depolymerization.The addition of Na⁺was designed to redistribute the surface charge,that means,soluble protein particles downsized but increased in number.The better surface activity thereby was given soybean 11S protein.The results were recorded as following.In this case,the emulsification and foaming value of soybean 11S protein caught 45.365 g/m² and 359.571%respectively.This commercial sodium caseinate achieved 38.211 g/m² and 333.342%.The treated soybean 11S protein under this condition had better surface activity.According to this experiment,the date of?_CMC and CMC value was collected as 54.8 m N/m and 0.1g/L.The characteristic of surfactant occured too.The HLB value was 10 which stand for better lipophilicity.The results of fluorescence spectroscopy,infrared spectroscopy and circular dichroism stated that the structure of the protein varied obviously from the one before the reaction of NaCl solution and oxidation.Beta form and random coil came to higher level.The whole molecule transformed into?+?from?.Its structure extand.The inner hydrophobic group of protein exposed,hydrophilic group and hydrophobic group redistributed.Hydrophobicity meliorated.After scanning by SEM,it refers to the particle size distribution.Because of the effects of NaCl solution and oxidative treatment soluble particles obtained still the increase in total number but decrease in the number of large grained and soluble member.That is to say,particles turned to be more uniform.The surface activity of 11S protein was improved finally.