Complex coacervation of protein/polysaccharide has found much interest for the 12 encapsulation of bioactive materials. The rheological properties of the coacervates of whey 13 protein/high methoxyl pectin (WPI/HMP) at different pH including 3.0, 3.5 and 4.0 were 14 investigated. The complex viscosity (η*) of the coacervate was decreased linearly with 15 frequency, showing the shear-thinning phenomenon of the coacervates. Furthermore, the 16 highest complex modulus (G*) and more compact coacervate were obtained at pH 3.5, 17 revealing less deformability and flow behaviour. All the coacervates showed higher storage 18 modulus (G') than loss modulus (G") indicating the formation of highly interconnected gel19 like structure. The maximum fracture stress was obtained at pH 3.5 revealing the highest 20 intermolecular interactions between WPI and HMP. It seems the high fracture stress and gel 21 strength of the complex coacervate would be suitable for encapsulation of bioactives. The 22 high aggregation was also achieved at pH 3.5, as the lower charge density of HMP should 23 make it more readily neutralized by whey protein binding. FTIR results showed the spectrum 24 of the coacervate was different from each individual biopolymer, related to their Corresponding author: Tel: +98 51 35425365; Fax: +98 51 35425406, Email: a.rafe@rifst.ac.ir ACCEPTED MANUSCRIPT 2 25 compatibility and intermolecular interactions between the functional groups of HMP and 26 WPI. Although, to get more insight toward dynamic rheological measurements in surveying 27 the interaction of any biopolymer blends, further work should be carried out for other 28 biopolymers.

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