Physicochemical and Emulsifying Properties of Whey Protein Isolate (WPI)-Dextran Conjugates Produced in Aqueous Solution

The physicochemical and emulsifying properties of protein and polysaccharide conjugates prepared under mild conditions were investigated. The covalently linked conjugates of whey protein isolate (WPI) and dextran (DX, 440 kDa) were produced by incubating aqueous solutions containing 10% WPI and 30% DX at pH 6.5 and 60 degrees C for 48 h. After purification by anion-exchange chromatography and affinity chromatography, the conjugate had a weight-average molecular weight (M-w) of 531 kDa and a radius of gyration (R-g) of 30 nm as determined by size exclusion chromatography-multiangle laser light scattering (SEC-MALLS); the molar binding ratio of WPI to DX was calculated to be similar to 1:1. The purified conjugate had significantly improved heat stability when subjected to 80 degrees C for 30 min and remained soluble over a range of pH from 3.2 to 7.5 and ionic strengths from 0.05 to 0.2 M in contrast to native WPI. The emulsifying ability and emulsion stability made with WPI-DX conjugate were also improved compared to WPI and gum arabic (an emulsifier containing naturally derived glycoproteins).