Rheological and structural characteristics of whey protein-pectin complex coacervates

Abstract

Complex coacervation of protein/polysaccharide has found much interest for the encapsulation of bioactive materials. The rheological properties of the coacervates of whey protein/high methoxyl pectin (WPI/HMP) at different pH including 3.0, 3.5 and 4.0 were investigated. The complex viscosity (η*) of the coacervate was decreased linearly with frequency, showing the shear-thinning phenomenon of the coacervates. Furthermore, the highest complex modulus (G*) and more compact coacervate were obtained at pH 3.5, revealing less deformability and flow behaviour. All the coacervates showed higher storage modulus (G′) than loss modulus (G″) indicating the formation of highly interconnected gel-like structure. The maximum fracture stress was obtained at pH 3.5 revealing the highest intermolecular interactions between WPI and HMP. It seems the high fracture stress and gel strength of the complex coacervate would be suitable for encapsulation of bioactives. The high aggregation was also achieved at pH 3.5, as the lower charge density of HMP should make it more readily neutralized by whey protein binding. FTIR results showed the spectrum of the coacervate was different from each individual biopolymer, related to their compatibility and intermolecular interactions between the functional groups of HMP and WPI. Although, to get more insight toward dynamic rheological measurements in surveying the interaction of any biopolymer blends, further work should be carried out for other biopolymers.