Interfacial, Emulsifying And Gelation Properties Of Soy Protein Modified By Polysaccharide

The functional properties of proteins could be improved by modification ofpolysaccharides. As functional material, protein modified by polysaccharide have gained wideattention because of their potential application in the field of food and medicine.Protein-polysaccharide interactions mostly originated from conjugation and electrostaticinteractions. Soy protein isolate (SPI)-maltodextrin (MD) conjugates were prepared byhigh-temperature, short-time dry-heating Maillard reaction, and the emulsifying properties ofSPI-MD conjugates were investigated in this study, which will provide theoretic supports forindustrialized production of protein-polysaccharide conjugates. The amphiphilic graftcopolymers were synthesized using Maillard reaction and controlled enzymatic hydrolysis.The interfacial and emulsifying properties of the amphiphilic graft copolymers were analyzed.Nanoparticles were prepared from soy protein-dextran conjugates by desolvation method. Thestructure, interfacial and emulsifying properties of the nanoparticles were investigated. Thetexture and gelation properties of soy protein-dextran conjugates gels were investigated. Thesoluble complexes of soy protein/sugar beet pectin (SBP) were formed by electrostaticinteractions. The stability mechanism of emulsions stabilized by soy protein/SBP complexeswas also investigated. The main results are as follows:(1) SPI-MD conjugates were synthesized using Maillard reaction under high-temperature(90,115and140°C), short-time (2h) dry-heating conditions. The loss of free amino groups inproteins and SDS-PAGE profile confirmed that SPI-MD conjugates were formed and higherdry-heated temperatures could increase the glycosylation degree. The emulsifying propertiesof SPI and SPI-MD conjugates were evaluated in oil-in-water emulsions. The emulsionsstabilized with SPI-MD conjugates (synthesized at140°C) exhibited higher emulsifyingstability and excellent storage stability against pH, ionic strength and thermal treatmentcompared with SPI-MD conjugates (synthesized at90,115°C), and SPI stabilized emulsions.This might be due to a greater proportion of conjugated MD in SPI-MD conjugates(synthesized at140°C) because of the higher glycosylation degree, and more conjugated MDon the droplet surface could provide steric effect and enhance the stability of the droplets inthe emulsions. (2) A emulsifier was prepared by conjugating soy β-conglycinin and dextran underdry-heated Maillard reaction followed by trypsin hydrolysis with the DH at2.2%and6.5%.Hydrolysates of β-conglycinin-dextran conjugates DH2.2%had a much higher interfacialpressure and fraction of protein adsorption at the oil-water interface compared withβ-conglycinin, β-conglycinin-dextran conjugates and hydrolysates of β-conglycinin-dextranconjugates DH6.5%. This might be due to controlled enzymatic hydrolysis could induceprotein unfolding and hydrophobic regions exposed to exterior, which could lead to increasein surface hydrophobicity of hydrolysates of β-conglycinin-dextran conjugates DH2.2%.Hydrolysates of β-conglycinin-dextran conjugates DH2.2%were capable of forming a fineemulsion against the changes of pH, ionic strength and thermal treatment, which remainedstable during4weeks of storage compared with β-conglycinin, β-conglycinin-dextranconjugates and hydrolysates of β-conglycinin-dextran conjugates DH6.5%stabilizedemulsions. This might be due to hydrolysates of β-conglycinin-dextran conjugates DH2.2%had much higher fraction of protein adsorption, which could led to more conjugated dextranon the droplet surface and improve the steric repulsion between the droplets, thus dropletaggregation and flocculation were inhibited.(3) Nanoparticles were prepared from β-conglycinin, β-conglycinin-dextran conjugatesand hydrolysates of β-conglycinin-dextran conjugates DH2.2%by desolvation method. Allthe nanoparticles exhibited spherical structures, as evidenced by dynamic light scattering,small-angle X-ray scattering and transmission electron microscopy. In addition, thenanoparticles prepared from hydrolysates of β-conglycinin-dextran conjugates DH2.2%hadan obvious core-shell structure. Furthermore, the nanoparticles prepared from hydrolysates ofβ-conglycinin-dextran conjugates DH2.2%showed higher interfacial pressure anddilatational modulus during absorption at the oil-water interface compared with β-conglycininnanoparticles and β-conglycinin-dextran conjugates nanoparticles. Emulsions stabilized withnanoparticles prepared from hydrolysates of β-conglycinin-dextran conjugates DH2.2%hadhigher emulsion stability after30days of storage. There was no significant change in themicrostructure of the emulsions stabilized with hydrolysates of β-conglycinin-dextranconjugates DH2.2%nanoparticles after30day of storage.(4) The gelation properties of β-conglycinin-dextran conjugates induced by MTGase was investigated. The gels of β-conglycinin-dextran conjugates exhibited higher G’, G’’, hardness,fracturability, springiness and cohesiveness values compared to those of dry-heatedβ-conglycinin, β-conglycinin and β-conglycinin-dextran mixture. The conjugated dextran inβ-conglycinin-dextran conjugates could inhibit extensive protein-protein interactions whichmight result in the formation of more ordered and stronger gel network structures duringMTGase cross-linking process.(5) β-conglycinin/SBP-MTGase, β-conglycinin/SBP-La and β-conglycinin/SBP-MTGase-La were prepared by MTGase and/or La cross-linking the soluble complexesof β-conglycinin/SBP. β-conglycinin/SBP-MTGase-La stabilized emulsions had higherstability against the changes of ionic strength and thermal treatment compared withβ-conglycinin, β-conglycinin/SBP-MTGase and β-conglycinin/SBP-La stabilized emulsions.This might be because that the soluble complexes of β-conglycinin/SBP were cross-linked byMTGase and/or La, which could form a layer by layer deposition interfacial film, and increaseemulsions stability against ionic strength and thermal treatment due to the steric repulsionbetween the oil drops.