Properties of edible films based on pullulan-chitosan blended film-forming solutions at different pH

Influences of solution pH on the properties of pullulan-chitosan blended (Pul-Chi) films and the rheological properties of film-forming solutions were investigated. The extended conformation of chitosan in a pH 4.0 solution increased the intermolecular interactions with pullulan compared to the more compact coiled form, resulting in higher tensile strength and barrier properties of the Pul-Chi film and higher viscosity of the film-forming solution. The water solubility (W-s) of the Pul-Chi film decreased to 35% above pH 4.0. Water content, thickness and percentage elongation (E%) all decreased with decreasing pH. Fourier Transform infrared spectroscopy (FTIR) analysis suggested that the formation of -NH3+ and intermolecular hydrogen bonds increased the amide II bending mode. At pH values below 4.0, shielding of the protonated amine groups caused a decrease in bending frequency. An X-ray diffraction (XRD) peak for crystallite chitosan was not observed in Pul-Chi films. The properties of Pul-Chi films depended on the conformation changes of chitosan molecules and can be controlled by pH.