Present work focused on the role of high methoxyl pectin (HMP) in rheology and physical stability of sodium caseinate (CAS) film-forming solution as well as mechanical and structural characteristics of its edible film. CAS-HMP films were fabricated at different blend ratio. Incorporation of HMP into CAS solution decreased pH value of the solution, acting as a natural acidifier. Turbidity and particle size distribution measurements indicated that some level of protein-polysaccharide interactions developed in 50CAS:50HMP and 25CAS:75HMP. Analysis of steady-state shear viscosity of film solutions showed a transition from Newtonian to shear-thinning flow behaviour by addition of HMP. Dynamic viscoelasticity evaluations revealed that the elasticity of solutions decreased by increasing HMP ratio. Physical stability of solutions was assessed over time using a Turbiscanner. All solutions showed distinct mechanisms of destabilization. 50CAS:50HMP and 25CAS:75HMP samples appeared to be the most stable solutions. Increasing CAS:HMP ratio from 100:0 to 25:75 increased the water solubility and elongation at break of edible films from 27.16 to 63.70% and 2.36 to 16.53%, respectively. SEM analysis exhibited a homogenous microstructure in 50CAS:50HMP and 25CAS:75HMP. DSC thermograms displayed lower glass transition temperatures in HMP-incorporated films. Presence of the interactions among biopolymers in biocomposites was confirmed by FTIR spectra.
Keywords: Composite film; Mechanical properties; Pectin; Physical stability; Rheology; Sodium caseinate.
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