Improvement Of Functional And Delivery Properties Of Soybean 7S Protein By High-pressure Homogenization Treatment

Soybean 7S protein(?-Conglycinin)is one of the major globulins in soybean protein,accounting for about 30%to 50%of the total soybean seed protein content,it is a conjugated trimeric glycoprotein.Soybean 7S protein has been studied extensively for its health benefits and physiological functions because it is rich in amino acids required by the human body.Besides,it also has good functional properties,and when used as a food ingredient in food production,it can not only increase the protein content of the product,but also improve the functional properties of the food,such as improving the taste,increasing elasticity,and improving water retention and oil retention,etc.However,treatments such as heating,alkali solubilization and acid deposition can lead to protein denaturation,resulting in reduced or lost functionality,thus limiting its application in the food industry.In order to improve the functional and delivery properties of soybean 7S protein,it was physically modified by using High-Pressure Homogenization(HPH)technology,which resulted in changes in the spatial structure and physicochemical properties,thereby improving its functional properties.The modified soybean 7S protein is used in the food system to increase its utilization space as an emulsifier and delivery carrier.This thesis first uses HPH pretreatment to modify soybean 7S protein as a support point and characterizes the structure and physicochemical properties of the physically modified soybean 7S protein(HPH-7S),including particle size,Zeta potential,spatial structure,solubility,surface hydrophobicity and functional properties.Then the HPH-7S protein was used to prepare the emulsion,and the protein concentration was used as a variable to determine the particle size distribution,flocculation index,storage stability,thermal stability,emulsification index,and interfacial adsorption protein content of the stable emulsion of different concentrations of HPH-7S protein.And then HPH-7S protein was used to encapsulate curcumin(CUR)to form HPH-7S/CUR nanoparticles.With CUR concentration as the variable,the encapsulation efficiency(EE%)and particle size are used as the indexes to optimize the addition concentration of CUR,the HPH-7S/CUR particles with excellent performance were prepared,and their structure,stability,antioxidant activity,and digestion characteristics are determined.The main results were as follows:(1)Soybean 7S protein was modified by using the HPH treatment(20,40,60,80,and 100 MPa),and the particle size of HPH-7S was 94.32 nm and the PDI was 0.248 at a homogenization pressure of 60 MPa,which showed a significant improvement relative to the particle size(262.3 nm)and PDI(0.871)of the non-HPH-treated 7S protein.The results of FTIR and fluorescence spectroscopy showed that the secondary structure content of HPH-treated soybean 7 S protein changed,in which the content of ?-turn gradually increased,the protein-peptide chains unfolded,the hydrophobic group was exposed,the tertiary structure was destroyed and rearranged.Surface hydrophobicity increased to 587.7 at a homogenization pressure of 60 MPa.Foaming,foaming stability,emulsification,and emulsion stability measurements confirmed that HPH treatment significantly improved the functional properties of soybean 7S protein.(2)HPH-7S protein-stabilized emulsions treated with 60 MPa pressure were successfully prepared using the HPH method as an emulsification technique,and the particle size distribution and flocculation index of the emulsions stabilized with different protein concentrations were measured,and the HPH-7S-stabilized emulsions had the lowest volume mean particle size(d4,3)of 2.68 ?m at HPH-7S protein concentration of 2.0%.The temperature stability and storage stability of the HPH-7S-stabilized emulsions were determined,and it was concluded that the HPH-7S-stabilized emulsions had better thermal and storage stability than the 7S-stabilized emulsions.The amount of interfacial protein adsorption was higher in the HPH-7S-stabilized emulsions than that in the 7S-stabilized emulsions,probably due to the fact that HPH pretreatment caused a certain degree of unfolding of the structure of the soybean 7S protein,exposing more hydrophobic groups,which increased the amphiphilicity of the protein molecules and made the protein more easily adsorbed to the oil-water interface,increasing the interfacial protein adsorption of the emulsions and enhancing the stability of the emulsions at the same time.(3)HPH-7S/CUR nanoparticles were prepared by an anti-solvent method.At a CUR concentration of 4 mg/mL,HPH-7S/CUR had an optimal particle size and encapsulation rate of 151.9 nm and 88.8%,respectively,with a zeta potential of-23.9 mV.The results of FTIR and fluorescence spectroscopy indicated that HPH-7S might bind to CUR through hydrophobic interaction,and the interaction force between HPH-7S and CUR molecules was greater than that between 7S and CUR without HPH treatment.pH stability measurements of HPH-7S/CUR showed that the particle size of HPH-7S/CUR was almost unaffected at pH values far from the isoelectric point of 7S protein(pH 4.0-5.0),maintaining a small particle size.In addition,HPH-7S was able to retard the degradation of CUR more effectively,with better thermal stability and improved bioaccessibility relative to untreated 7S protein.Moreover,HPH-7S can better improve the antioxidant activity of CUR in an aqueous solution.