A pH indicator film based on chitosan and butterfly pudding extract for monitoring fish freshness.

A pH indicator film was prepared by mixing natural polymeric chitosan (CH) with natural dye from butterfly pudding extract (BP). The films were determined by color changes at different pH value, absorbance, thickness, moisture content, swelling property, water contact angle, mechanical property, barrier property, and microstructure of films. The structural change of film was analyzed by Fourier transform infrared spectra. The application to monitor fish freshness was also studied. The prepared film was sensitive to the changes in pH value and showed distinct color changes from pink purple to yellow, with pH value ranging from 1 to 14. The films showed visible color changes from purple-blue to dark green during fish preservation. The total volatile basic nitrogen (TVB-N) content and pH value changes of tilapia were closely related to the visual color changes in film. The result indicated that the fabricated film was a highly pH-sensitive film for monitoring fish freshness.