Intelligent Film Based on Agar and Natural Dye from Arnebia Euchroma Root Extracts as a Visual Colorimetric Indicator

Abstract

Natural dyes extracted from Arnebia euchroma root were immobilized in agar to prepare a colorimetric pH sensing film, which showed an obvious color change from red to blue in the pH range 3.0-12.0. The UV-vis spectra of natural dye in solution and in the sensing film were studied. FT-IR and UV-vis spectra of the colorimetric films showed that Arnebia euchroma root extracts (AEREs) were successfully immobilized into agar matrix. Mechanical properties (ultimate tensile strength, elongation to break, and Young’s modulus) of pH indicator films with and without AEREs were contrasted. Color response of this pH sensing film to NH3 standard solution was also researched respectively and results showed that the colorimetric films with lower content of AEREs were more sensitive towards volatile ammonia. The colorimetric indicator film is expected to provide a convenient, non-destructive and visual method to help the estimation of fish spoilage during storage.