Study On The Physicochemical And Functional Properties Of Whey Protein Isolate-Dextran Conjugate

Whey protein isolate (WPI) and dextran were used to prepare WPI-dextran conjugate bythe dry-heating treatment in our present research. The physicochemical characteristics,conformation and functional properties of the conjugates were systematically investigated inorder to provide the theoretical knowledge, which could supply the guidance for theapplication of protein-polysaccharides grafted reaction in the food industry.Significant changes in A294, browning intensity, free amino groups content andSDS-PAGE profile showed that whey protein isolate-dextran conjugate was successfullyformed using dry-heating treatment via Maillard reaction. When the length of sugar chain wasincreased, the graft reaction was relatively difficult. Compared to the native WPI, the contentof lysine and arginine in the conjugate was decreased and the maximal fluorescence intensityat405nm was obviously increased, which was in accordance with the typical characteristic ofthe Maillard-type products. The measurement results of fluorescence, surface hydrophobicityindex and solubility index showed that the hydrophobicity of WPI could be suppressed due tothe covalent attachment of high molecular weight dextan chain. Far-UV CD spectra showedthat the α-helix and β-turns were decreased while β-sheet and random coil were increasedafter the WPI-dextran mixture was treated by the dry-heating. Moreover, it was observed bySEM that the surface structure of the conjugate WPI was different with the native WPI, whichwas that the typical globular structures was dispersed and the disordered sheet structureappeared. The emulsifying properties and the freeze–thaw stability of oil-in-water emulsionsstabilized by WPI were significantly enhanced by the covalent attachment of dextran; thecharge is not the main factor which determine the stability of the emulsion system after theξ-potential analysis. The thermal denaturation temperature of WPI was enhanced in somedegree by the glycosylation; the steric hindrance effect induced by the high molecular weightdextan chain could suppress the heat-induced aggregation among the neighbouring proteins inaqueous solution. During the gelation process, the modulus curve of G’ and G’’ in theWPI-dextran conjugate (G150) was significantly modified, which showed that the mechanismof gelation in WPI was intrinsically altered by the covalent attachment of dextran.The results showed that the WPI-dextran conjugate own strong DPPH radical scavenging ability, indicating that the antioxidant capacity of MRPs was increased. The conjugates wereused as wall material to encapsulate the fish oil and the data show that the core materialscould be well encapsulated with a high productive and efficiency. Meanwhile, the oxidativestability of the microcapsules products was highly enhanced.