A visual pH sensing film using natural dyes from Bauhinia blakeana Dunn

Natural dyes extracted from the flower of Bauhinia blakeana Dunn were immobilized in chitosan to prepare a colorimetric pH sensing film, which color changed from red to green in the pH range 2.2–9.0. The UV–vis spectra of the natural dyes in solution and in the sensing film were studied. The characteristics of the pH sensing film, including response time, reproducibility, reversibility, stability toward light and the storage time, were investigated. Since pH value of a pork or fish sample concerns its freshness, the pH sensing film is expected to provide a convenient, non-destructive and visual method to help the estimation of pork and fish spoilage in ambient conditions.