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

Abstract

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.